- Created by: Phoebeologb
- Created on: 26-03-18 16:45
Eukaryotes/eurkaryotic cell: complex cells and includes all animal and plant cells.
Prokaryotes/prokaryotic cell: simple and smaller cells like bacteria.
Plant and Animal Cells Similarities:
- Nucleus: contains genetic material that controls the activities of the cell.
- Cytoplasm: gel-like substance where most of the chemical reactions happen; it contains enzymes that controls these chemical reactions.
- Cell membrane: holds the cell together and controls what goes in and out.
- Mitochrondia: where respiration reactions take place (respiration transfers energy to the cell so it can work)
- Ribosomes - involved in the translation of genetic material in the synthesis of protein
- Cell wall: made of cellulose; supports and strengths the cell.
- Vacuole: contains cell sap (weak solution of sugar and salt) and maintains the internal pressures to support the cell.
Bacterial cells: and lot smaller than animal or plant cells and have these subcellular structures:
- Chromosomal DNA: controls cells activites and replication. It floats freely in cytoplasm.
- Cell membrane
- Plasmid DNA: small loops of extra DNA that isn't part of the chromosome. Plasmids contain genes for things like drug-resistance and can be passed between bacteria.
- Flagellum: a long hair-like structure that rotates to make the bacterium move - it could be move the bacteria away from harmful substances (toxins) and towards beneficial things like oxygen.
Multicellular organisms contains cells with different structures.
Specialised cells: different structures that make the cell adapt to their function.
In sexual reproduction, the nucleus of the egg cell and sperm cell fuse together to produce a fertilised egg which then turns into an embryo. The nucleus of the sperm cell and egg cell both contain a half number of chromosomes that would normally be in a body cell - this is called a haploid. After fertilisation, the resulting cell will have a full amount of chromosomes.
Egg cell function: to carry the female DNA and to nourish the developing embryo in early stages. It is adapted to this function as: it contains nutrients in the cytoplasm to feed the embryo, it has a haploid cell and after fertilisation, the membrane changes shape to stop any more sperm getting in so the offspring end up with the right DNA.
Sperm cell function: to transport male DNA to the female egg. It is adapted to its function as: it has a long tail to swim to egg, it has lots of mitochrondria in middle section to provide the energy needed to swim to egg cell, it has an acrosome at the front of its head where it stores enzymes needed to digest its way through the membrane of egg cell and finally, it contains a haploid nucleus.
Ciliated Epithelial Cells function: to move substances - the cilia (hair-like structures) move substances in one direction, along the surface of the tissue. Some of epithelial cells have cilia on the top surface of the cell and line the surfaces of organs.
Example: there are lots of ciliated epithelial cells that are on the lining of the airways because they move mucus (and other trapped particles) up the throat to be swallowed and so it doesn't go to the lungs.
Changes in Microscopes
Microscopes use lenses to magnify images: they increase the resolution (the quality and sharpness of microscope) of the image.
Light Microscopes (1590s): pass light through specimen, they let us see things like the nucleus and chloroplasts and you can also study living cells with them.
Electron Microscopes (1930s): use electrons to pass through specimen, they have higher magnification and resolution than light microscopes and so let us much smaller things in detail like the internal structures of a mitochrondria and chloroplast. This allows us to have a greater understanding of how cells work and their subcellular structures, although the electron microscope cannot be used for living cells).
To use a microscope: make sure your specimen is thin so a light can shine through it, take a clean slide and pipette and use to add drops of stain to the specimen if transparent (so you can see it better), then place a cover slip over it gently so no air bubbles are trapped under it, then clip the slide onto the stage. Select the lowest powered objective lens and use the coarse adjustment knob to move the stage upwards until the specimen is in focus. Then adjust the focus with the fine adjustment knob and then measure the specimen's diameter to get a field of view. If you need to see your specimen in more focus, change to a high objective lens.
Total Magnification = Eyepiece lens magnification x objective lens magnification
Image size = Magnification x Real size
Example: x100 magnification
Giraffes Make Kangeroos Disappear Cowardly Making Mad Noises... Pathetic
Giga (x12) Mega(x9) Kilo(x3) Deci(x-1) Centi(x-2) Mili (x-3) Micro (x-6) Nano (x-9) Pico (x-12)
Enzymes are biological catalysts that quicken the rate of reaction. They reduce the need for high temperature.
Enzymes have special shapes so that they can catalyse reactions. The substrate is the molecule changed in the reaction.
Every enzyme has an active site - the part which joins to the substrate to catalyse a reaction. Enzymes usually only join to one substrate because of their high specificity for their substrate and this is because: for an enzyme to work, a substrate needs to join with their active site. If the substrate's shape doesn't fit into the active site, then the reaction will not be catalysed.
This is called a 'lock and key' mechanism because the lock is the active site and the specific key is the substrate.
Enzymes are biological catalysts that quicken the rate of reaction. They reduce the need for high temperature.
Enzymes have special shapes so that they can catalyse reactions. The substrate is the molecule changed in the reaction.
Every enzyme has an active site - the part which joins to the substrate to catalyse a reaction. Enzymes usually only join to one substrate because of their high specificity for their substrate and this is because: for an enzyme to work, a substrate needs to join with their active site. If the substrate's shape doesn't fit into the active site, then the reaction will not be catalysed.
This is called a 'lock and key' mechanism because the lock is the active site and the specific key is the substrate.
Factors that Affect the Rate of Reaction
pH: Enzymes work best at ph 7 but not always: pepsins are a type of enzyme that breaks down proteins in your stomach. Enzymes there work best at pH 2 (it is well suited to acidic conditions). If the pH is too high or low, the pH will interfere with the bonds holding the enzyme together: it will change the shape of the active site and denature the enzyme.
Temperature: Enzymes optimum temperature is between 30-40 degrees. A higher temperature increases the rate of reaction until it gets so hot; some of the bonds holding the enzyme together will break. This changes the shape of the active site and makes the substrate not fit in it anymore; it is now denatured.
Substrate Concentration: The higher the subtrate concentration, the faster the rate of reaction because the enzyme is more likely to meet up with a subtrate and catalyse it. However, if there is more subtrate than there is active sites, the rate will be constant as all of the active sites will be full.
- The enzyme amylase catalyses the breakdown of starch to maltrose.If starch is present, iodine solution will turn change from browny-orange to blue-black.
- Place a test tube in a flask of water. Heat up the test tube to 35 degrees and then add the buffer solution (ph5), then the amalyse solution and then the starch solution. Now sample the mixture in a spotting tile every 10 seconds until the starch is no longer present - you will be able to find this out by adding the indicator the colour being browny-orange.
- Repeat the experiment again using different pHs to find out how this affects the rate of reaction.
- For this experiment, you can do 1000 divided by the time. For any other experiment, you can do: the change in something divided by the time.
Enzymes break bigger molecules down into smaller molecules so that they can be used for growth and other life processes:
- many molecules in our food is too big to go pass through the walls of our digestive system, so digestive enzymes break them down into smaller, soluble molecules.
- Plants store energy in the form of starch. When plants into energy, amylase break down the starch into smaller molecules (maltrose and other sugars) and this can then be respired to transfer energy to be used by the cells.
Carbohydrases convert carbohydrates into simple sugars. Starch is broken down by amylases into maltrose and other sugars. Cabohydrates can be synthesised by the joining of simply sugars. Glycogen synthase is an enzyme that joins up a chain of glucose to form glycogen.
Proteases convert protein into amino acids. Proteins are made by the joining of amino acids.
Lipases convert lipids into fatty acids and glycerol. (the fatty acids will lower the pH of the place they are in). Lots of enzymes are used to to synthesise lipids from fatty acids and glycerol.
Test for sugars using Benedict's regeant: Add benedict's regeant (blue) to a sample and heat it in a 75 degrees water bath. If the test's positive, it will form a coloured precipitate (brick red). The higher the concentration of the sugars, the the further the colour change goes from blue to brick red.
Test for starch using iodine: Add iodine solution to the starch. If starch is present is will burn from orange-brown to blue-black. If starch is not present, is stays brown-orange.
Emulsion Test for Lipids: Shake the test subject with ethanol until it dissolves, then pour solution into water. If there are any lipids present, they will precipitate out of the liwuid and show up as milky emulsion. The more lipids, the more milky it will be.
Biuret Test for Proteins: Add drops of potassium hydroxide so the solution becomes alkaline. Add copper (II) sulfate solution (bright-blue). If there is protein present, it will turn purple.
Energy in Food
Calorimetry: food being burnt to see how much energy it contains.
- You will need dry food because that burns easily. Weigh the food, add a set volume of water to the boiling tube with a thermometer and use the flame of the burning food to heat up the water - keep doing this until there is no food left. Then measure the temperature of the water again.
ENERGY of food (JOULES) = Mass of water x Temperature change x 4.2
Energy per gram = Energy in food/mass of food.
Diffusion, Osmosis and Active Transport
Diffusion - the net movement of particles from an area of high concentration to an area of low concentration. Small molecules can diffuse through membranes: amino acids, glucose water and oxygen. They move down the concentration gradient.
Osmosis - the net movement of water molecules through a partially permeable (holes in the membrane that are big enough to let water molecules in but too small to let bigger molecules, like sucrose through) membrane from a region of high concentration to low concentration. The water acts to balance the water concentration on either side of the membrane - it can also pass through the membrane both ways because water movement is random. The water molecules in an area of high concentration has a steady net flow as it fills up an area with lower concentration (a solute solution) - the solute solution becomes more dilute as more water molecules travel to the area.
Active transport: the net movement of particles across a membrane through a concentration gradient from an area of low concentration to an area of high concentration using the energy tranferred during respiration. Examples: there is a higher concentration of nutrients in the gut than in the blood, the nutrients diffuses naturally into the blood but sometimes, there is a lower concentration of nutrients in the gut than in the blood so active transport allowes nutrients to be taken in the lood, despite the fact that the concentration gradient is the wrong way.
- This experiment shows how water molecules go through the partially permeable membrane of potatoes to balance the low concentrate of the solute solution - this solution will be sucrose solution.
- Prepare sucrose solution ranging from water to highly concentrated sucrose solution. Cut the potatoes in same sized pieces and use a balance to measure them. Leave the potatoes in the solution for 40 mins and then weigh the potatoes again.
- The bigger the mass, the more dilute the substance is and so the more water was able to pass through the potato membrane.
- The decrease in mass shows how water molecules from the potato have moved to try and balance out the lower concentration of water molecules in the solution.
Calculate percentage change = (final mass - initial mass) divided by initial mass x 100.
Nucleus contains genetic material in the form of chromosomes (coiled up lengths of DNA molecules). Body cells have two copies of chromosomes, making them a diploid cell.
- Interphrase - when the DNA all spreads out in long strings to increase subcellular structures like mitochrondria and ribosomes. It then duplicates its DNA which forms X shaped chromosomes.
- Prophrase - the chromosomes get shorter and fatter. The membrane in the nucleus breaks down, making the chromosomes free.
- Metaphrase - the chromosomes line up at the centre of the cell.
- Anaphrase - Cell fibres pull the chromosomes apart, making the two arms of each chromosome go the opposite ends of the cell.
- Telophrase - Membranes form around each set of chromosomes - this becomes the nuclei of the two cellw - the nucleus has now been divided.
- Cytokinesis - the cytoplasm and cell membrane then divide to form two daugther cells that are identical and also identical to the parent cell.
Cell Differentiation - when a cell changes to become specialised for its job - this allows subcellular cells to work more efficiently.
Cell Division - by mitosis.
Plants also use cell elongation -this is when the plant cells expand, making the plant grow.
All growth in animals happens by cell division. Animals tend to grow when they are young until their reach full growth. When your young, cells divide at a much faster rate but when you're an adult, you cells divide mostly for repairing old or damaged cells. This means that cell differentiation.
When plants grow in height, it is mainly due to cell elongation - cell division usually just happens in the tips of the roots and shoots but plants grow continuously. So plants will also continue to differentiate and develop new parts.
Cancer - uncontrollable cell division. The rate at which cells divide by mitosis is controlled by the genes in an organisms DNA. If there is a change in one of these genes that control cell division, the cell will start dividing uncontrollably. This results in a mass of abnormal cells called a tumour. If the tumour invades and destroys surrounding tissue, it is called cancer.
Percentile Charts monitor growth.
The 50th percentile is 50%.
Stem cells - are undifferentiated cells - depending on what instructions are given, stem cells can divide by mitosis to become new cells which can then differentiate. Stems cells are found in embryos - these embryonic stem cells have the potential to divide into any cell they want (all the different types of cells in our body came from stem cells). Adults also have stem cells but only in places like bone marrow - they aren't as versatile as embryonic stem cells because they can only produce certain cell types. Adult stem cells are repair cells.
Meristems - the only plant cells that divide by mitosis. Meristem tissue is found in areas that plants grow like in the roots. Meristems produce unspecialised cells that are able to divide into any cell type. But unlike human stem cells, these cells divide and differentiate into any type of cell for as long as the plant lives.
The unspecialised cells go on to form specialised tissue like xylem and phloem.
Stem Cells in Medicine
- Adult stem cells cure diseases - example: sickle cell anaemia can sometimes be cured by a bone marrow transplant.
- Scientists have extracted stem cells from embryos and started growing them. Under certain conditions, the stem cells can be stimulated to differentiate into specialised cells.
- stem cells can create specialised cells that replace the ones that have been damaged by injury or disease, like: new cardiac muscle cells could be transplanted in someone with heart disease. Stem cells have the ability to cure diseases. But there are many risks like?
- Tumour development - stem cells divide very quickly If scientists are unable to control this, a tumour may develop.
- Disease transmission - If a donor cell is infected by a virus and the doctors don't see it, it will be passed onto the recipient and so make them sicker.
- Rejection - If the transplanted cells are not grown using patient stem cells, the patient's body may recognise the cells as foreign, triggering an immune response to get rid of them. The patient can take drugs to supress their response but this makes them suspectible to diseases.
- Reseach using embroyonic stem cells raises ehtical issues because a embryo is a potential human life but others think curing patients who are suffering is more important than the potential life of an embryo.
The Brain and Spinal Cord
Spinal cord - long column of neurones (nerve cells) that run from the base of the head down to the spine. At places down the cord, neurones branch off and connect with other parts of the body. The spinal cord relays information to the rest of the body.
The brain (made up of billions of interconnected neurones) have different functions:
Cerebrum (largest part of brain) - divided into two halves called cerebral hemispheres. The right hemisphere controls the left muscles and vice versa. Different parts of the cerebrum are responsile for things including: memory, language, vision, intelligence and movement.
Cerebellum - Responsible for muscle coordination and balance.
Medulla oblongata - Controls unconscious activities like breathing and your heart rate.
Brain tissue can be accessed with surgery but it is very risky.
- CT scanners use X-rays to produce an image of the brain. A CT scan shows the main structure of the brain, but not the function of them. However, if the CT scan shows a diseased/damaged brain and the patient has lost some function, doctors can work out the function.Like, if an area of the brain is damaged and the patient can't see, the function of the area affected is vision.
- PET scanners - use radioactive chemicals to show which parts of the brain are active when a person is inside a scanner. They are very detailed and can be used to investigate both structure and brain at the same time. They are useful in studying disorders that change brain activity as they show areas of the brain that are unusually active/inactive like, Alzheimer's disease, active in some areas of the brain are reduced compared to a normal brain.
It is hard to repair damage to the nervous system - neurones in the Central Nervous System don't readily repair themselves and scientists haven't found ways of repairing nervous tissue in the CNS. It also is not easy to access the nervous system and so it is difficult to treat like, it is not possible to remove a tumour from certain parts of the brain. Treatments for problems in the nervous system may lead to permanent damage like, if a person who has injured their spinal cord need treatment, the spinal cord can be damaged further during the operation, leading to permanent damage.
The Central Nervous System
Made up of neurones that go to all parts of the body.
Sensory receptors - groups of cells that can detect a change in your environment (a stimulus). There are different sensory receptors like in your eye, it detects light while your skin detects touch and temperature change.
When the stimulus is detected by receptors, the information is converted to a nevous electrical impulse and sent along the sensory neurones to the CNS. The CNS coordinates the response and the impulse then travels through the CNS to the relay neurones.The CNS sends information to an effector along a motor neurone and then the effector responds accurately. Reaction time - the time it takes you to react to a stimulus.
Neurones Transmit Information Rapidly
Neurones have a cell body with a nucleus (plus the other subcellular structures). The cell body has extensions that connect to other neurones - dendrites and dendrons carry the nerve impulses towards a cell body and axons carry nerve impulses away - some axons are surrounded by myelin sheath which acts as a electrical insulator, speeding up the electrical impulses. Neurones can be very long and this also speeds up the impulse because connecting with another neurone slows down the impulse, so one long one is much quicker.
Sensory gland (looks like an arm) - One long dendron carries impulses from receptor cells to the cell body which is located in the middle of neurone (like an elbow).One short axon carries the impulses away from the body and towards the CNS (the fingers).
Motor neurone - many short dendrites that carry nerve impulses from the CNS to the cell body (is is at the start of the neurone). One long axon (with myelin sheath) carries nerve impulses from the cell body to effector cells.
Relay neurone - many short dendrites carry nerve impulses from the sensory neurones to the cell body. An axon carries nerve impulses from the cell body to the motor neurones.
Synapses and Reflexes
the connection between two neurones is called a synapse. The nerve signal is transferred by chemicals (neurotransmitters), which diffuse across a gap. The neurotransmitters then set off a new electrical signal in the next neurone. The transmission of a nervous impulse is very fast,but it is slowed down a bit at the synapse because the diffusion of neurotransmitters across the gap takes time.
Reflexes - automatic, rapid responses to stimul; reducing the chance of being injured.
- the passage of information in a reflex (receptor to effector) is a reflex arc.
- The neurones in the reflex arc go through the spinal cord or an unconscious part of the brain.
- When a stimulus is detected by receptors, impulses are sent along the sensory neurone to the relay neurnoe in the CNS. When the impulse reaches a synapse between the sensory and relay neurone, they trigger neurotransmitters to be released and this causes impulses to be sent along the relay neurone.When the impulses reach the synapse between the relay and motor neurone, the same thing happens. Impulses are then sent along the motor neurone to an effector (a muscle or gland). Then the muscle/gland contracts and moves your part of body away from the stimulus. As you don't have to think about this response, it is much quicker than normal responses.
Reflex in Eyes
Very bright light can damage your eyes.
Light receptors in your eye detect bright lights and send a message along the sensory neurone to the CNS (brain). The message then travel along the relay neurone to the motor neurone, which then tells circular muscles in the iris to contract, making the pupil smaller.
Cornea - refracts (bends) light into the eye.
Iris - controls how much light enters the pupil.
Retina - light sensitive part that is covered in receptor cells called rods and cones - they detect light.
Rods - more sensitive in dim light but can't sense colour.
Cones - sensitive to different colours but aren't good in dim light.
The information from light is converted into electrical impulses. The optic nerve carries these impulses from the receptors to the brain.
Focusing on Near and Distant Objects
To look at distant objects: the ciliary muscle relaxes, which allows the suspensory ligament to pull tight. This pulls the lens into a less rounded shape which makes the eye refract light less.
To look at close objects: the ciliary muscle contracts, which allows the suspensory ligament to slacken. This makes the lens more rounded, so more light is refracted.
Long-sighted people can't see close objects - this is because the lens is in the wrong shape and so doesn't refract enough light or the eyeball is too short. Light from near objects is brought into focus behind the retina. You can use glasses or contact lenses with a concave lens to correct it.
Colour Blindness and Cataracts - the most common form of it is red-green colour blindness, caused when the red and green cones aren't working properly in the retina. There is no cure because the cones can't be replaced. Cataracts is a cloudy patch on the lens, which stops light from entering the eye normally and so people with cataracts are likely to have blurred vision. They may also experience colours looking less vivid or difficulty seeing in light. This can be treated with an artifical lens to replace the faulty one
Sexual Reproduction and Meiosis
Sexual reproduction - genetic information from a mother and father is combined to form an offspring. The mother and father produce gametes (reproductive cells) in animals, these are the egg and sperm cells. Gametes are haploids - at fertilisation the male gamete fuses with a female gamete to produce a fertilised egg (zygote - it ends up with full set of chromosomes) - the zygote undergoes cell division by mitosis, to develop into a embryo - it has characteristics from both parents due to the mixture of chromosomes.
Gametes are produced by meiosis (doesn't produce identical cells). In humans meiosis only happens in reproductive organs. Before the cell divides, it duplicates it DNA , one arm of each X is identical. In the first division in meiosis, the chromosomes line up in pairs in the centre of the cell.One chromosome from each pair is from the mother and father. The pairs are then pulled apart so the new cells have a copy of each chromosome. Each new cell will have a mixture of chromosomes from the mother and father.
In the second division, the chromosomes line up at the centre and the arms are pulled apart. You get four haploid daughter cells - these are gametes and each gamete only has a single set of chromosomes, each gametes are all genetically different.
Asexual and Sexual Reproduction
When cells reproduce assexually, they divide by mitosis, resulting in two diploid daughter cells (identical to each other and the parent cell. Sexual reproduction involves meiosis and the production of genetically different haploid gametes, which fuse to form a diploid cell at fertilisation.
Advantages of asexual reproduction - can produce lots of offspring very quickly because the reproductive cycle is so fast. For example, e.coli (bacteria) can divide in half an hour. This can allow organisms to colonise an area very quickly. One parent is needed - this means that the organism can reproduce in whatever conditions are favourable without waiting for a mate - aphids reproduce assexually in the summer when there is plenty of food.
Advantages of a sexual reproduction - creates genetic variation with individuals having different characteristics, which means if conditions change, some individuals will still survive and over time this can lead to natual selection and evolution as species become better adapted to their new environment.
Disadvantages of Asexual Reproduction - there is no genetic variation so if the environment changes, all of the population would likely be affected. Like the Black Sigatoks is a disease that affects banana plants, which reproduce asexually. If there is an outbreak out the disease, its likely that all banana plants in the population will be affected.
Disadvantages of Sexual Reproduction - takes more time and energy than asexual reproduction, so fewer offspring is produced: organisms need to find and attract mates which takes a long time - a male bowerbird build structures out of twigs and dance to impress females. Two parents are needed for sexual reproduction and this can be a problem if individuals are isolated. For example, polar birds live alone, so male polar bears walk up to 100 miles to find a mate.
DNA are strands of ploymers made up of repeating units called nucleotides. Each nucleotide consists of one sugar molecule, one phosphate molecule and one 'base'. The sugar and phosphate form a backbone to the DNA strands. The sugar and phosphate molecules alternate. One of the four different bases joins to each sugar - adenine, thymine, guanine and cytosine. A DNA molecule has; double helix (a double stranded spiral) , each base links to another base on the opposite strand of a helix.
Adenine - Thymine Guamine - Cytosine <---- this is called complementary base pairing and they are joined by weak hydrogen bonds.
How to extract DNA from fruit cells - mash some strawberries up and put them in a beaker containing, detergent and salt. The detergent will break down the cell membranes to release the DNA. the salt will make the DNA stick together. Filter the mixture to get the froth and big, insoluble bits of cell out and then gently add cold alcohol to the filtered mixture. The DNA will start to come out the mixture because it is insoluble in cold alcohol. it will appear as a white stringy precipitate that can be fished out with a glass rod.
DNA controls the production (synthesis) of proteins in a cell. Proteins - made up of chains of amino acids - each different protein has a different number and order of amino acids. The amino acid chains fold up to give each protein a different shape which means they have different functions - this is why enzymes have different active sites to catalyse certain reactions.
gene - a section of DNA that codes for a particular protein. It is the order of the bases that decides the order of the amino acid and so amino acids are joined together to make proteins in the order of the bases in a gene. Many areas of DNA are non-coding (don't code for any amino acids) but they are still involved in protein synthesis. All of the organism's DNA makes up the organism's genome.
A mutation - a rare, random change to an organism's DNA base sequence that can be inherited. If a mutation happens in a gene, it produces a genetic variant (a different version of the gene). The genetic variant may code for a different sequence of amino acids, which may change the shape of the final protein and so its activity. The activity of the enzyme might increase/decrease/stop altogether. This could end up changing the characteristics of an organism. For example, XDH is an enzyme in fruit flies that makes their eyes red. Fruit flies with no XDH have brown eyes because they can't produce red pigment. Mutations also happen in Non-coding DNA.
Transcription - when the DNA can't get out of the nucleus because it is too big and so mRNA has to be made in order for protein synthesis. What happens is: RNA polymerase bind to the region of non-coding DNA at the start of the gene. The RNA polymerase then unzips the DNA and moves along the DNA, uses the coding DNA in the gene to make the mRNA. Base pairing ensures that the mRNA is completementary to the gene. Once it is made, the mRNA moves out of the nucleus and joins with a ribosome. mRNA is shorter than DNA and is a single strand.
Translation - when the mRNA meets with the ribosome to form polypeptides (protein). Amino acids are brought to the ribosome by a transfer RNA (tRNA). The order of the amino acids brought to the ribosomes is the same order of the base triplets in the mRNA. Base triplets = codons.
Part of the tRNA is called anticodons and they have completementary bases to the codon. The pairing of the codon and the anti-codon is to ensure that the amino acids are brought the ribosome in the correct order. The amino acids are then joined together by the ribosome and make a polypeptide (protein).
Before transcription starts, the polymerase has to bind to the non-coding region of the DNA. If a mutation happens, the RNA polymerase could find is easier or more difficult to bind with the DNA. How well the RNA polymerase binds to the DNA also affects how much protein is produced. Depending on the function of the protein, the phenotype of an organism may be affected.
The Work of Mendel
In one experiment, Mendel crossed two pea plants of different height - a tall pea plant and a dwarf pea plant. The offspring produced were all tall pea plants.
He then bread two of the tall offspring together. He found out when two tall offspring crossed, three tall plants were produced for every 1 dwarf plant. 3:1 RATIO.
Mendell had shown that the height of the pea plants were determined by the seperately inherited 'hereditary units' from each parent. It showed that the tall plants were dominant over the unit, t, dwarf plants. Mendel also found out other dominant characteristics of the pea plant too, like purple flowers dominated white flowers.
Mendel reached three conclusions: characteristics in plants are determined by 'hereditary units, hereditary units are passed on from parents unchanged (one unit from each parent) and the hereditary unit can be dominant or recessive - if the offspring had both dominant and recessive, the dominant characteristic will be expressed.
His work was new and cutting-edge. We now know that 'hereditary units' are genes but at the time, scientists could not understand Mendel's work because they had to background knowledge about genes. It wasn't tell after his death that people realise how significant his work was.
Alleles - different versions of genes. Everyone has two versions - one on each chromosome in a pair ; if they are the same then it's homozygous and if they are different then its heterozygous. Some alleles are dominant and some are recessive. Dominant alleles could be homozygous or one dominant and one recessive. For an organism to display recessive genes, it must be two recessive ones. The inheritance of a single characteristic is called monohybrid inheritance. You can find the ratio using a punnet sqaure too.
More Genetic Diagrams
There are 23 pairs of chromosomes - the 23rd pair is labelled ** or XY. Males have XY - the Y causes the male characteristic whilst females have ** - the ** combination allows female characteristics to develop. There is an equal chance (50%) of having a girl or a boy.
All eggs have an x but the sperm cell has either an X or a Y.
Family pedigree (a damily tree of genetic disorders) shows monohybrid inheritance, for example: cystic fibrosis is a recessive allele and so because it is recessive, someone with two recessive alleles will have the disease.
Sex-linked Genetic Disorders
A characteristic is sex-linked if it's located on the X or Y chromosome.
The Y is smaller than the X and so carries fewer genes. Most genes are carried on the X chromo.
As men only have one X-chromosome, they only have one allele for sex-linked genes. As men have one only one allele, the characteristic of the gene is shown even if it recessive. - this means men are more likely to show the recessive characteristics of the sex-linked gene than women.
Colour blindness is caused by a faulty allele carried on the X chromosome. Women need two copies of the recessive gene to be colourblind whilst men only need one. A woman with one recessive allele is a carrier. Homophilla is another sex-linked disorder. It's caused by a faulty allele carried on the x-chromosome, so it is inherited in the same way as colour blindness.
Humans can have the following potential blood types: O, AB, A or B.
The gene for these are: I/\0, I/\A or 1/\B.
IA and IB are codominant with each other - when someone has both, they are expressed by AB (one isn't more dominant than the other).
However, IO is recessive so when you get IOIA or IOIB, you will only see the affect of a or b, Type A or Type B.
You can only get O if you have IOIO.
You can predict blood groups by punnet squares.
Variation - differences in a same species. Genetic variation within a species is caused by different alleles which can lead to different phenotypes (characteristics that an organism displays). Genetic variation can be caused by new alleles uprising from mutations or sexual reproduction because the alleles are being combined in different ways in offspring. There tends to be a lot of genetic variation within a species due to neutral mutations but is can also be caused by the environment. For example: a plant that is luscious and green as it has been near a window vs. a yellow plant not next to a window. These are acquired characteristics (you get them overtime).
Most variation in phenotype is determined by a mixture of genetic and environmental factors: for example, the maximum height that an animal or plant could grow to is determined by its genes but whether it actually grows to that height depends its environment.
Alleles - mutations are changes to the base sequence of DNA.- when they occur in a gene, it results in an allele or different version of gene. A small mutation can have a big effect on an organisms phenotype but this is rare. For example: it might result in the production of proteins that are so different that they can no longer carry out their function. Cystic fibrosis: a mutation causing protein, that controls the movement of water and salt into and out of cells, to stop working. This leads to sticky, thick mucus in the lungs and digestive system, making it difficult to breath or digest.
Human Genome Project
HGP aim - find every human gene. A complete map of the human genome, 20,500 genes, was completed. All genes have been found and now they are want to find out what they do.Scientists have identified 1800 genes related to disease, which has potential for new medical discoveries.
Prediction and Prevention of diseases - many common diseases like cancer are caused by the interaction of different genes (and lifestyle factors). If doctors knew what genes makes people susceptible to what diseases, individually tailored advice can be given on the best diet/lifestyle to avoid problems. Doctors can also check us regularly to ensure early treatment to the disease we are suceptible to.
Testing and treating for inherited disorders - caused by faulty alleles in a person's genome. Scientists are now able to identify the genes and alleles that cause an inherited disorder much more quickly thanks to the HGP. Once the allele has been identified, people may be testing for the disorder and it may be possible to develop cures or treatments for it.
New and better medicines - HGP highlights some variations within people - some variations affect how our body will react to diseases and treatments for them. Scientists can use this knowledge to deisgn drugs tailored for people. Tests can identify whether or not someone with breast cancer will respond to a particular drug/the dosage appropiate.
Drawbacks of the HGP
Increased stress - knowing from an early age that you are susceptible to a disease may cause panic. Like if someone knew that they were susceptible to brain disease, they might panic everytime they get a headache.
Gene-ism - people with genetic disorders may come under pressure to not have children.
Discrimination by employers and insurers - life insurance could become impossible to get if you have any genetic liklihood of a serious disease. Employers may discriminate agains people who are genetically likely to get a disease.
Natural Selection and Evidence for Evolution
Natural Selection - predation, competition for resources like food and diease act as selection pressures (they affect the chances of surviving and reproducing). Some organisms that have characteristics that make them better adapted to selection pressures in their environment are more likely to survive and breed sucessfully. This means the alleles responsible for the useful characteristics will be passed on to the next generation. Some individuals that are less adapted to the selection pressures may be less able to compete and thus are unlikely to survive or breed.
The beneficial characteristics become popular over time.
Bacteria Provide Evidence for Evolution - bacteria could develop mutations that will enable them to resist antibiotics - this will make more likely to survive and reproduce which will make the resistance of antibiotics more common over time. Bacteria have become better adapted to their environment and selection pressures (antibiotics) and therefore this provides evidence for evolution.
Evolution and Darwin
Fossils - any trace of an animal/plant that lived a long time ago (mosty found in rock). The deeper the rock, the older the fossil; if you arrange the fossils in chronological order, gradual changes can be observed. The is evidence for evolution because it shows how species have developed over billions of years.
Charles Darwin - came up with the theory of evolution by natural selection. He noticed that there were variations in members of the same species and that those with characteristics that are most suitable to their environment were likely to survive - this characteristic could then be passed onto offspring. Wallace - his observations provided evidence for the theory of evolution by natural selection - he realised that warning colours used by some species (like butterflies) to deter predators from eating them is a benefical characteristic that has evolved by natural selection. But Darwin's book 'On the Origin of Species' made scientists pay attention to his theory. He had lots of evidence to support his theory which is why he is so popular compared to Wallace.
Natural evolution by natural selection has made us understand lots of things today like how all life changes through the process of evolution and that we all come from a common ancestor.
It has affected some areas of biology:
Conservation - we now know that animals the importance of genetic diversity and how it helps populations adapt to changes in the environment. This has led to conservation projects to protect species.
Classification - if we all come from the same ancestor, then we are all related in some way. We can now classify species based on how closely related they are.
Antibiotic resistance - we now know that bacteria can become resistance and so people know that they need to finish their course of antibiotics to prevent the antibiotic-resistance characteristic from spreading and scientists are developing new antibiotics to fight these antibiotic-resistant bacterium.
Humans and chimpanzees evolved from the same common ancestor 6 million years ago. Humans=homonids.
Ardi 4.4 million years ago - ardipithecus ramidus: found in Ethiopia, her feet suggest she climbed trees as she had ape like toes to grasp trees, long arms, short legs, brain the size of a chimp but structure of her legs and hands suggest she walked upright - she didn't use her hands to help her walk.
Lucy 3.2 million years ago - australopithecus afarensis: found in Ethopia, she had arched feet which were more adapted to walking than climbing (no ape like toes), the size of arms and legs were between those of an ape and human, her brain was larger than Ardi's, the structure of her leg bones and feet suggest she walked upright more efficiently than Ardi.
Turkana 1.6 million years ago - Richard Leakey found Turkana boy and other fossils in Kenya. Turkana boy was: a homoerectus, had short arms and long legs more like a human, a larger brain than Lucy (more human-sized) and the structure of his legs and feet suggested he was better adapted to walking upright compared to Lucy. WE ARE HOMOSAPIENS
Homo habilis(2.5-1.5 million years ago) - made simple tools called peble tools by hitting rocks together to make sharp flakes. These could be used to scrap meat from bones or crack bones open.
Homo erectus (2-0.3 million years ago) - sculpted rocks into shapes to produce complex tools like hand-axes. This could be used to hunt, dig, chop and scrape meat from bones.
Homo neanderthalis (300,000-25000 years ago) - more complex tools like flint tools, pointed tools and wooden spears
Homo sapiens (200,000 years ago-present) - flint tools widely used, pointed tools including arrowheads, fish hooks, buttons and needles appeared around 50,000 years ago.
You can find out how old the rocks were from: looking at the structure of the tool, stratigraphy (the study of rock layers) as the deeper the rock, the older the rock and carbon-containing minerals, stone tools often found with this. Carbon-14 can be used to date something like a wooden handle.
Pentadactyl Limb and Classification
limbs with five digits - you see pentadactyl limbs in many species like mammals and reptiles. In each species, the pentadactyl limb has the same structure but different structures, for example: human hands and bat wings are similar in structure but humans don't use theirs to fly.
The similarity in bone structure provides evidence that we have all evolved from a common ancestor.
Classification - living organisms are classified into 5 kingdoms: animals, plants, fungi (yeast and mushrooms), prokaryotes (single celled organisms without a nucleus) and protists (eukaryotic single-celled organisms like algae).
kingdoms are then subdivided into smaller groups - phylum, class, order, family, genus and species. The five kingdoms however is a but out of date. Over time, technology has developed further and our understanding of things like biochemical processes and genetics has increased - scientists can also compare RNA sequences - this to led to rethinking about of classification system and the proposal of the three domain system: using RNA sequencing, Woese found that some members of the prokaryotic kingdom where not closely related at all and so the the group should be split into Archea and Bacteria
Woese then thought that all organisms should be split into three groups called domains:
Archea - Organisms that look similar to bacteria but are different - as differences in their DNA and RNA sequence show. They were first found in hot springs and salt lakes.
Bacteria - this domain contains true bacteria like E. coli.
Eukarya - this domain includes a broad range of organisms including fungi, plant, animals and protists.
These groups are divided into: Kingdom, Phylum, Class, Order, Family, Genus and Species.
Selective breeding - when humans artifically select the plants or animals that are going breed so that genes for particular characteristics stay in the population. Organisms are bred to develop useful/attractive features like: animals that produce more meat or milk, dogs with a good, gentle temperament and plants that produce much bigger fruit. This is the basic process involed in selective breeding:
- From your existing stock, select the ones which have the characteristics you want.
- Breed them with each other
- Select the best offspring and breed them together.
- Continue this process over the several generations until the desired trait gets stronger and stronger.
- Selective breeding has been around for thousands of years and has produced edible flowers and domesticated animals.
Selective Breeding is useful because:
- Agriculture: genetic variation means some cattle will have better characteristics for producing meat than others. To improve meat yield, a farmer could select cows and bulls with these characteristics and breed them together and their offspring until the farmer would get cows with very high meat yield.
- Medical reseach: In studies investigating reasons behind alcoholism, rats have been bred with either a strong preference for alcohol or a weak preference for alcohol. This allowed reseachers to compare the differences between two different types of rats, including differences in their behaviour and in the way their brains work.
It reduces the gene pool - the number of different alleles in a population. This is because the best animals are always used for breeding - and they are all closely related. This is known as inbreeding and can cause health problems because organisms are at a higher risk of inheriting harmful genetic defects because of inbreeding - like pugs have breathing problems. This leads to ethical considerations, particularly if organisms are bred to have negative characteristics for research. If a new disease appears, as there isn't variation, most/all of them will be affected by it.
Tissue culture - when you grow cells on an artificial growth medium. Whole plants can be grown with tissue culture very quickly, in a little space an can be grown all year round - these are all clones. You can create clones with the same beneficial features e.g. tasty fruit or pesticide-resistance.
Process: First choose the plant you want to clone based on its characteristics (a good fruit crop). You remove several small pieces of tissue from the parent plant (you get the best results if you take tissue from the fast growing root or shoot tips). You grow the tissue in a growth medium containing nutrients and growth hormones (this is down under aseptic conditions to prevent harmful microbes that could harm the plant).
As the tissues produce shoots and roots, they can be moved to potting compost where they continue growing.
Animal Tissue Culture
Animal tissue culture - often used for medical reseach because you can carry out experiments on them like the effect of glucose on cells in the pancreas by growing pancreatic cells. You can look at the effects of substances or environmental change on the cells of single tissue, without the complications of the whole organism.
1) A sample of tissue is extracted from the animal.
2) The cells in the sample are pulled apart using enzymes.
3) They are placed in a culture vessel where they are bathed in growth medium full of nutrients so they can grow and multiple.
4) After several cell divisions, the cells can be split up again and placed in seperate vessels to encourage further growing.
5) Once the tissue culture is grown, it can be stored for future use.
Restriction enzymes - recognise specifc sequences of DNA ad cut the DNA at these points - the pieces of DNA are left with sticky ends.
Ligase enzymes are used to join two DNA oieces together at their sticky ends.
recombinant DNA - when two pieces of DNA are stuck together.
Vector - used to transfer DNA into a cell. Plasmids: small, circular molecules of DNA that can be transferred between bacteria. Viruses: insert DNA in the organisms they infect.
How Genetic Engineering works: The DNA you want to insert (like the gene for human insulin) is cut out by a restriction enzyme. the vector DNA is then cut open using the same restriction. They are both left with sticky ends and are mixed with ligase enzymes. The ligase enzyme is then used to join the two pieces of DNA together by their sticky ends to make a recombinant DNA. The recombinant DNA is then inserted in other cells. These cells can now use the gene that you inserted to make the protein you want. E.g bacteria containing human insulin gene can be grown in a fermenter to produce insulin for diabetic people.
IN AGRICULTURE: crops can be genetically modified to resist herbicides (chemicals that kill plants). Making crops herbicide resistant means farmers can spray crops to kill weeds and not the crops - this increases crop yield.
Disadvantages: transplanted genes may get out into the environment e.g. pesticide-resistance gene may be picked up by weeds, creating a 'superweed' variety. Genetically modified crops could also affect the food chain and even some people's health.
IN MEDICINE - researchers have managed to transfer human genes that produce useful proteins in cows and sheeps. Animals that have organs suitable for organ transplantation into humans might also be produced in the future.
Disadvantages: it can be hard to predict what effect modifying its genome will have on the organism - many geneticaly modified embryos don't survive or will suffer from health problems in the future.
Reasons why? Some people want to genetically engineer crops as it makes them resistant to insect pests - this would increase crop yield and reduce the need for chemical pesticides. There is a bacteria (bacillus thuringiensis, Bt) which produces toxins that kill many insect larvae harmful to crops. The gene for the Bt toxin is inserted into crops, like corn and cotton, which then produce the toxin in their stems and leaves - making them resistant to insect pests. It is also good because it is resistant only to pests and so cannot affect humans, animals or other insects - however, long term effects of exposure to Bt crops aren't known.
The world's population is increasing and this means that global flood production must increase too so that we all have access to enough food that is safe and provides enough nutrients - this is called food security. GM crops can be used to increase food production - like crops that are genetically engineered to be resistant to pests or to grow better in drought conditions can help improve crop yield. Some crops can even been engineered to combat deficiency disease like Golden Rice is genetically engineered to produce a chemical that converts in the body to vitamin A.
Disadvantages: Many people argue that people that are hungry cannot afford for, not that they isn't any about - so they need to tackle poverty first before introducing GMOS. There are fears that countries will become dependent on companies that sell GM seeds. Sometimes poor soil is the main reason why crops fail, and even GM crops won't survive.
Other Techniques To Increase Food Production
If soils are poor, applying fertiliser is the best way to increase crop yield. Fertilisers contain minerals essential to plant growth like nitrates and phosphates - they replace the nutrient that has been lost in soils due to previous crops. However, excess fertiliser can cause eutrophication to happen in lakes.
Instead of pest-resistant genes, you can use biological control methods that use other organisms (like predators or parasites) to reduce pest numbers. For example, cane toads were introduced into Australia to eat bettle that were damaging the crops.
Biological control is long lasting compared to pesticides and are less harmful to wildlife. However, introducing new organisms can cause problems: cane toads are now a pest themselves because they poison the native species that eat them.
Health and Disease
WHO says health is 'a state of complete physical, mental and social well-being, and not merely the absense of disease'
Disease - a condition where part of the organism doesn't function properly.
Communicable disease - a disease that can be spread between individuals
Non-communicable disease - a disease that can't be transmited between individuals. They include cancer.
If you are affected by one disease, you are more susceptible to others as you body weakens when fighting the disease.
Communicable diseases are spread by pathogens. Pathogens are organisms such as viruses, bacteria, fungi and protists.
Viruses - a protein coat around a strand of genetic material. They have to infect living cells in order to reproduce.
The lytic pathway: The virus attaches itself to a specific host cell and injects its genetic material into the cell. The virus uses proteins and enzymes in the host cell to replicate its genetic material and produce the components of a new virus. The viral components assemble and the host cell splits open, allowing the new viruses to infect more cells.
The lysogenic pathway: The injected genetic material is cooperated with the DNA (genome) of the host cell. The viral genetic material gets duplicated everytime the host cell divides - but the virus is dormant and no new viruses are made. Eventually a trigger (like the presence of a chemical) causes the viral genetic material to leave the genome and enter the lytic pathway.
Chlamydia - bacterium that can only reproduce inside host cells. It doesn't really cause any symtoms but can cause infertility in men and women. The spread of chlamydia can be reduced by wearing a condom when having sex, screening individuals so they can be treated for the infection or avoiding sexual contact.
HIV (Human Immunodeficiency Virus) - it kills white blood cells which a important in the immune response. HIV infection eventually leads to AIDS. This is when an infected person's immune system deterioriates and everything fails - the person becomes vunerable to infections by other pathogens from this. HIV is spread by infected bodily fluids (semen, blood, vaginal fluids). One of the main ways to prevent it is to use a condom during sex, drug users should avoid sharing needles. Medication can reduce the risk of an infected individual passing it on to someone else during sex (or a mother to her baby during pregnancy) so screening and proper treatment is important too.
Most plant leaves and stems are covered in waxy cuticles which provides a barrier to stop pathogens from entering or pests from damaging them. It also stops water from collecting on the leaf, which could stop pathogens from entering them that are transferred between plants in water.
Plant cells are surrounded by cell walls made up of cellulose and this forms a physical barier against pathogens that make it past the waxy cuticle.
Chemical barriers: They produce chemical barriers to protect themselves from pathogens or any damage caused to the plant by, for example, producing antiseptics that kill bacterial and fungal pathogens. Some of these chemicals can be used in drugs to treat human diseases/relieve symptoms like: quanine comes from the bark of the cinchona tree and is used to treat malaria. Aspirin is used to relieve pain and it comes the chemical in the barks and leaves of willow trees.
Plant Diseases Detection
You can detect plant diseases from observation: plant pathologists recognise symptoms e.g galls (abnormal growths) might indicate crown gall disease in different plants like apple trees. However, some plants may show symptoms (like yellow leaves) of a disease which is actually caused by environmental factors like nutrients deficiency. By changing environmental conditions, it can be possible to check whether or not a plant is diseased. Different pathogens are spread in different ways so plant pathologists can identify the distribution of the disease to find out what pathogen is involved.
Laboratory-based diagnostic testing allows accurate identification of certain pathogens:
Detecting antigens: pathogens have unique molecules on their surface called antigens. Antigens from a pathogen will be present in a plant infected with that pathogen and it can be detected in a sample of plant tissue (using monoclonal antibodies). The detection of an antigen unique to the pathogen allows that pathogen to be recognised and the disease diagnosed.
Detecting DNA: If a plant is infected by a pathogen, the pathogen's DNA will be in the plant's tissue. Scientists have techniques which allow them to detect the smallest amount of pathogen DNA in a sample of plant tissue, allowing them to identify the particular pathogen present.
Physical barriers: The skin acts as a barrier to pathogens and if it gets damaged, blood clots quickly seal cuts and keep microorganisms out. Hair and mucus in your nose trap particles that could contain pathogens. Cells in your trachea and bronchi (airways in lungs) also produce mucus, which traps pathogens. Other cells that line that the trachea and bronchi are cilia and these hair-like structures move the mucus up the throat to be swallowed.
Chemical barriers: The stomach produces hyrochloric acid that kills most pathogens that are swallowed. The eyes produce a chemical called lysozyme (in tears) which kills bacteria on the surface of the eye.
If pathogens do make it into your body, your immune system kills them. The white blood cells travel around your body, patrolling for pathogens. B-lymphocytes (type of white blood cells) that are involved in the specific immune response (this is a response to a specific pathogen): Every pathogen has a unique molecule (like protein) on their surface called antigens. When your b-lymphocytes come across an antigen on a pathogen, they start producing antibodies - these bind to the pathogen so it can be found and destroyed by other white blood cells - these specific antibodies won't lock onto any other pathogen. They produce rapidly, flowing around the body to find similar pathogens.
Memory Lymphocytes & Immunity
When a pathogen enters the body for the first time, the response is slow because there aren't many b-lymphocytes that can make the antibody needed to lock on to the antigen. Eventually, the body will produce enough of the right antibody to overcome the infection - during this, the person will show symptoms of the disease. As well as antibodies, memory lymphocytes are produced in response to the foreign antigen and these remain in the body for a long time and remember a specific antigen. The person is now immune as their immune system responds much faster the second infection: if a same pathogen enters the body, there will be more cells that recognise it and therefore they will produce antibodies - faster and stronger - the second response gets rid of infection before you start showing symptoms.
Immunisation: to avoid getting ill, you can be immunised against some diseases. Immunisation involves injecting dead or inactive pathogens into the body that are antigenic (they carry antigens) - they are harmless and antibodies destroy them. The antigens though trigger memory lymphocytes to be made so that if the same type of pathogen gets into the body, there will already be memory lymphocytes that can cause a fast secondary immune response. You are less likely to get the disease.
Pros and Cons of Immunisation
Pros: Epidemics can be prevented if a large percentage of the population are immunised: even the people who aren't immunised would be unlikely to get the disease because there would be fewer infected people that can pass it on - this is known as 'herd immunity'. But if a large number of people aren't immunised, the disease will spread quickly through them a lots of people will be ill. Some diseases like smallpox were wiped out by immunisation programmes.
Cons: Immunisation doesn't always give you immunity. You can sometimes have a bad reaction to a vaccine (e.g. swelling or maybe fevers). But bad reactions are very rare.
Antibodies are produced by b-lymphocytes. Monoclonal antibodies are produced from many clones of a b-lymphocyte - all antibodies are identical + will target one specific protein antigen. Lymphocytes don't divide easily while tumour cells divide a lot but don't produce antibodies, so they grow easily. You can fuse a mouse b-lymphocyte with a type of tumour cell called myeloma cell, to create a hybridoma (these cells can be cloned to get lots of identical cells and divide quickly to produce antibodies (monoclonal antibodies). These can then be collected and purified.
You can make monoclonal antibodies bind to anything you want. e.g. an antigen that's only found on the surface of one type of cell. This makes them useful because they will only target this certain molecule and so can use them to target specific cells/chemicals in your body.
Used in pregnancy tests: a hormone (HCG) is found in the urine of only pregnant women. In a pregnancy test, the stick you urinate on, has blue beads with antibodies attached to it - these antibodies are targeting the hormone. The test ***** has the same antibodies and they are stuck to the *****. When a pregnant lady pees on the stick, the hormone attaches to the blue beads, the urine then moves up the stick to where the test ***** is and the hormone binds to the antibody which makes the blue beads stick too. It turns blue to show that the woman is pregnant. If she isn't, the blue beads will be carried still, but there will be nothing to stick to the antibodies (so no blue).
Cancer cells have proteins on their cell membrane that aren't found on normal body cells - these are called tumour markers. In the lab, you can make monoclonal antibodies which bind to these tumour markers which can be used to help diagnose and treat cancer.
Antibodies are first labelled with a radioactive element; labelled antibodies are given to a patient through a drip, they are carried around the body until it comes into contact with a cancer cell - the antibodies bind with the tumour markers + pictures can be taken of the patient's body with a camera that detects radioactivity; the cancer will show up as a bright spot. Doctors can see where the cancer is, the size and if it is spreading.
An anti-cancer drug is attached to monoclonal antibodies and is given to the patient through a drip; the antibodies go around the body patrolling for a specific cell (cancer cells) until they come across a tumour marker and bind to it. The drug kills the cancer cells but doesn't kill the normal cells around it. This is better than other treatments like other drugs and radiotherapy that affects normal body cells too. So the side-effects of an antibody-based drug are lower than other treatments.
Find blood clots: when blood clots, proteins in blood join together to form a solid mesh. Monoclonal antibodies are developed to bind to these proteins + can be injected into a patient with a radioactive element so a camera can pick up the bright spot wheerever the blood clot is.
Antibiotics work by stopping processes in bacterial cells, but not in host organisms. For example: soem antibiotics inhibit the building of bacterial cell wals to stop the bacteria from dividing and eventually kills them, but has no effect on cells in the human host. Different antibiotics kill different types of bacteria but don't destroy viruses as viruses reproduce using host body cells, which makes it difficult to develop drugs that destroy the virus without destroying the body cell.
Penicillin is an antibiotic and was discovered by Alexander Fleming - he noticed that one of the dishes had mould on it and that the area aroung the mould was free of bacteria. The mould was producing penicillin and killing the bacteria.
Once a potential drug has been discovered to fight against disease it goes through preclinical and clinical testing:
- Preclincal testing - drugs first tested on human cells and tissues in the lab. However, you can't use human cells to test a drug a drug that affects the whole body system like a drug for blood pressure must be tested on a whole animal. The next step is to test the drug on live animals. This is to that the drug works, to find out how toxic it is and to find the best dosage.
Preclinical and Clinical testing
Preclinical testing: when a drug is first tested on human cells and tissue in the lab. However, you can't use human cells/tissues if the drug affects the whole body system, for example: a drug for blood pressure needs a whole body. Next, it is tested on live animals to see whether the drug has the affect intended, if it is safe and what dosage is needed.
Clinical testing: The drugs can now be tested on healthy human volunteers - this is so the scientists can check that there will be no harmful side effects when the body is normal again. If this is passed, the drug can be tested on ill patients - an optimum drug dosage is found (this means a dosage is most effective and has little side effects).The patients are split into two groups: one tested with the new drug and the other is a placebo (they are given a fake drug) - this is so the placebo effect can take place (when people are expecting the drug to work and therefore feel better, but the drug actually does nothing). Clinical trials are blind - the patient nor doctor don't know which groups they are in until results are gathered. This is so that doctors aren't subconsciously influenced by their influence. When the drug finally passes all these tests, it needs to be approved by a medical agency before it can be used to treat patients - the drugs are as safe and effective as possible.
Antibiotics and Antiseptics
Practical: Bacteria (and other microorganisms) are cultured (grown) in a growth medium - containing carbohydrates, minerals, proteins and vitamins needed to grow - this can either be nutrients broth solution or solid agar jelly. Bacteria grown in agar plates with form visible colonies on the surface of the jelly, or will spread out to given an even coating.
To make an agar plate, hot agar jelly is poured into a petri dish and when the jelly's cooled and set, inoculating loops can be used to transfer microogranisms to the agar jelly or a sterile dropping pipette and spreader can be used to get an even covering of bacteria. The microorganisms then multiply.
In the lab at school, cultures of microorganisms are kept at about 25 degrees because harmful pathogens are unlikely to grow at this temperature but outside of schools, scientists may culture microorganisms at higher temperatures to provide optimum conditions for growth.
Effects of Substances on Bacterial Growth
Antibiotics kill bacteria inside whilst antiseptics kill bacteria outside the body. You can thus investigate both antiseptic and antibiotic effects on cultures of bacteria and also because plants produce antiseptics, you can also test this. This is how you do it:
Place paper discs soaked with different antibiotics on an agar plate with an even coating of bacteria. The antibiotic should diffuse into the agar jelly - antibiotic-resistant bacteria will continue to grow around the paper whilst non-resistant bacteria will die. A clear area will be left where bacteria has died: the inhibition zone. Use a paper without antibiotics to make sure that the difference between the growth of the bacteria around the control disc and around one of antibiotic discs is due to the effect of the antibiotic alone (not because of the paper, etc..). Leave the paper for 2 days and the more effective the antibiotic, the larger the inhibition zone.
Aseptic: The petri dishes and growth medium must be sterlised before use. This can be done by placing them in an autoclave, which uses steam at high pressure and temperature to kill any microorganisms present. An incoulating loops should also be sterilised via a hot flame to kill any microorganisms. Liquid bacterial cultures should be kept in a culture vial with a lid and the lid should be tapped to the petri dish to prevent microbes from the air getting in . The petri dish should be stored upside down to stop drops of condensation from falling onto the agar jelly.
Risk factors - things linkd to the increase in likelihood that a person will develop a certain disease - these are unavoidable (e.g. age, gender might make them more likely to get a disease). But some lifestyle factors can change like:
- Smoking - a major risk factor associated with cardiovascular disease (diseases associated with the heart of blood vessels). This is because nicotine in smoke, increases heart rate which increases blood pressure - high blood pressure can damage artery walls, which contributes to the build up of fatty desposits in the arteries. These deposits restrict blood flow and increase the risk of a heart attack or stroke. Smoking also increases the risk of blood clots in arteries which can restrict blood flow, leading to a heart attack or stroke.
Ofter lifestyle factors are associated with different diseases: a diet with too much or too little nutrients = malnutrition and diseases associated like scurvy or vitamin C deficiency.
Not enough exercise and having a diet high in fat and sugar are risk factors for obesity.
Drinking too much alcohol can cause liver diseases like cirrhosis (scarring of liver). This is because alcohol is broken down by enzymes in the liver and some of the products are toxic. Drinking too much can cause permanent liver damage.
As well as smoking, there are other risks associated with cardiovascular disease including: alcohol, lack of exercise, and a diet high in saturated fat. Many non-communicable diseases are caused by several different risk factors interacting with each other, including cancer, liver and lung disease and obesity. Obesity is a risk factor for other non-communicable disease like type 2 diabetes and cardiovascular disease.
Non-communicable diseases can have wide-ranging effects including: where there is high levels of obesity, smoking or excess alcohol concentration, there is likely to be an occurence of certain non-communicable diseases like cardiovascular or liver disease. This can put pressure on the resources of local hospitals (on the beds, staff and etc..) Non-communicable disease are costly at national level because the NHS provides resources for treatment of patients all around the UK and also some people suffering from a non-communicable disease may not be able to work. Therefore, a reduction in the number of people able to work and the increase in resources can affect a country's economy. As well as being costly, non-communicable diseases are very common and in developing countries, malnutrition is also a big problem due to people not having access to enough food.The high cost and occurence of these diseases can hold back the development of a country on a global level.
Body Mass Index - BMI decides if someone is overweight (25-29.9), underweight (below 18.5), normal (18.5-24.9) or obese (30 and above).
BMI = weight (kg) / height (m) squared
If you eat a high fat, high sugar diet and don't do exercise, you are likely to take in more energy than you use. The excess energy is stored as fat, so you're more likely to have a high bmi (obese). However, BMI isn't reliable because athletes have lots of muscle which weighs more than fat, so they will come out with a high BMI even though they're not overweight.
Waist-to-hip ratio: waist circumference / hip circumference
The higher your waist-to-hip ratio, the more weight you're likely to be carrying around your middle. A ratio above 1.0 for males and above 0.85 for females indicate you're carrying too much weight around your middle - this is known as abdominal obesity. It puts you at greater risk of developing obesity-related health problems.
Treatments for Cardiovascular Disease
Arteries - blood vessels that carry blood away from the heart. Cholestrol - fatty substance that the body needs to make cell membranes. But too much cholesterol in the blood can cause fatty deposits to build up in the arteries which restricts the flow of blood. Deposits occur where the artery wall has been damaged by e.g. high blood pressure. The fatty acids can also trigger blood clots to form which can block the blood flow completey, causing the heart muscle to be deprived from oxygen (if it happens in the artery supplying the heart muscle) - this can cause a heart attack and a blockage in the brain can deprive the brain from oxygen and cause a stroke.
Lifestyle changes can treat or reduce CVD - people will CVD are adviced to eat a balanced diet which is low in saturated fats, exercise regularly, lose weight or stop smoking.Lifestyle changes are recommended first. Some drugs reduce the risk of heart attacks or strokes - statins reduce the amount of cholesterol in your bloodstream and this slows down the rate at which fatty deposits form; reduce the risk of a heart attack or stroke. However, they can cause bad side effects like aching muscles and even liver damage. Anticoagulants are drugs which make blood clots less likely to form but this can cause excessive bleeding if the person is hurt. Antihypertensives reduce blood pressure and this helps to prevent the damage of blood vessels and so reduce the risk of fatty acids from forming. However, they can cause side effects like headaches.
Surgical Procedures for CVD
Stents are tubes that are inserted inside the arteries - this keeps them open which makes sure that blood can pass through to the heart muscles, lowering the risk of a heart attack. But overtime, the artery can narrow again and the stents can irritate the artery and make scar tissue grow. The patient also takes drugs to stop blood clotting on the stent.
If part of the blood vessel is blocked, a piece of a blood vessel from elsewhere can used to bypass the blocked section = coronary bypass surgery.
The whole heart can be replaced with a donor heart - however, the new heart doesn't always start pumping properly and drugs need to be taken to stop the body from rejecting it. These drugs have side effects as they make you more susceptible to infections. There is always a risk of blood clotting, infection and bleeding.