SNAB - Biology - Topic 2

Notes on the entire of SNAB AS Biology Topic 2. They may have been more useful to create than to actually revise from, but hopefully they'll be useful! :)

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  • Created by: Katherine
  • Created on: 14-05-15 10:17
What is the role of mucus in the lungs?
To trap any dust, debris or microorganisms that enter the airways.
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The mucus is continually removed by...
The wave like beating of cilia that cover the epithelial cells, lining the tubes of the gas exchange system.
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Why is the mucus of people with CF different?
The mucus is different as it is drier than usual, resulting in a sticky mucus layer that the cilia cannot move
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The sticky mucus in the lungs has two major effects on health, these are:
It increases the chances of lung infection and it makes gas exchange less efficient.
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What are epithelial cells?
Epithelial cells form the outer surface of many animals. They line the cavities and tubes within the animal, and cover the surfaces of internal organs. The cells work together as a tissue known as epithelium.
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What are the epithelium in the walls of the alveoli and capillaries like?
Squamous - the very thin flattened cells fit together like crazy paving. The cells can be less than 0.2um thick.
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What are the epithelium in the walls of the small intestine like?
They extend out from the basement membrane. These column shaped cells make up columnar epithelium. The free surface facing the intestine lumen is normally covered in microvilli, which greatly increase the surface area.
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What are the epithelium in the trachea, bronchi and bronchioles?
They are ciliated epithelial cells with cilia on the free surface. These cilia beat and move substances along the tube they line. The ciliated columnar epithelium of the gas exchange airways looks stratfied, but it is in contact with membrane.
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How sticky mucus increases the chances of lung infections:
Microorganisms become trapped in the mucus in the lungs, and some can cause illness being pathogens. The mucus is normally moved by cilia to the acid where it is destroyed, but with CF the mucus layer is so sticky that it can't.
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Does mucus production continue in a person with CF?
Yes. The airways build up layers of thickened mucus. There are low levels of oxygen in the mucus, partly because oxygen diffuses slowly through it, and because the epithelial cells use up more oxygen in CF patients. Harmful bacteria thrives here.
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How does the immune response make mucus thicker in people with CF?
White blood cells fight the infections within the mucus but as they die they break down, releasing DNA which makes the mucus even sticker. Repeated infections can eventually weaken the body's ability to fight the pathogens, damaging gas exchange syst
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Why might failure to move mucus create a problem?
Pathogenic microorganisms have time to multiply, resulting in illness or infection.
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Why does swallowing mucus reduce the risk of infection?
Acid in the stomach kills the microorganisms
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The effect of increase in size on surface area:
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Substance that diffuse into or out of a cell move down a...
Concentration gradient
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How are the gradients maintained?
By the cell continuously using the substances absorbed and producing waste.
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The effect of size on gas exchange:
The larger an organism, the more exchange has to take place to meet the organism's needs. Larger multicellular organisms have more problems absorbing substances because of the size of the organism's surface area compared with its volume.
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Surface area to volume ratio is:
The size of the organisms surface area compared with its volume. Calculated by dividing an organisms total surface area by volume.
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If an organism gets larger, what happens to its surface area?
The surface area per unit of volume gets less. Gas exchange is slower
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What type of organism can rely on outer body surface for gas exchange?
Organisms with very small volume, or in larger organisms that have a high enough surface area to volume ration such as worms with a flattened shape.
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How do larger organisms increase gas exchange?
They have a variety of special organs that increase the surface area for exchange, increasing the surface area to volume ration. E.g. a mammal's lungs provided a large surface area for gas exchange. Digestive systems provides a large surface 4 food.
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Features of a good gas exchange surface:
Large surface area of the alveoli, numerous capillaries around the alveoli, thin walls of the alveoli and capillaries mean that there is a short distance between alveolar air and blood in capillaries.
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The rate of diffusion is dependent on three properties of gas exchange surfaces:
Surface area, concentration gradient, thickness of the gas exchange surface.
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Why is the rate of diffusion dependent on surface area?
The rate of diffusion is directly proportional to the surface area. As the surface area increases the rate of diffusion increases.
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Why is the rate of diffusion dependent on concentration gradient?
Rate of diffusion is directly proportional to the difference in concentration across the gas exchange surface. The greater the concentration gradient, the faster the diffusion.
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Why is the rate of diffusion dependent on the thickness of the gas exchange surface?
Rate of diffusion is inversely proportional to the thickness of the gas exchange surface. The thicker the surface the slower the diffusion.
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What is Ficks Law?
Rate of diffusion = (Surface area x difference in concentration)/(thickness of the gas exchange surface)
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How does sticky mucus affect gas exchange?
The sticky mucus layer in the bronchioles of a person with cystic fibrosis tends to block these narrow airways, preventing ventilation of the alveoli below the blockage. This reduces the number of alveoli providing a surface area for gas exchange.
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Blockages are more likely to occur at the narrow ends of the airways, and these often allow air to pass when a person breathes in but not out. How does this damage the lungs?
This results in over inflation of the lung tissue beyond the blockage. This can damage the elasticity of the lungs.
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Why do people with CF tend to find it difficult to take part in physical exercise?
Their gas exchange system cannot deliver enough oxygen to their muscle cells. The oxygen is needed for the chemical processes of aerobic respiration, which release the energy used to drive the contraction of the muscles during exercise.
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Why is CF mucus so sticky?
It contains less water than normal. The reduced water level is due to abnormal salt and water transport across the cell surface membranes caused by a faulty transport protein channel in the membrane.
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What is the general structure of an amino acid?
An amine group (NH2), a carboxylic acid group (COOH), a hydrogen (H) attached to a central carbon atom. Each type of amino acid has a different side chain (R).
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What is the primary structure of a protein?
The sequence of amino acids in the polypeptide chain.
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What is the secondary structure of a protein?
The chain of amino acids twists to form an a helix. Within the helix, hydrogen bonds form between the C=O of the carboxylic acid and the -NH of the amine group of different amino acids.
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What is the tertiary structure of a protein?
A polypeptide chain bends and folds to produce a precise three dimensional shape.
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What is a conjugated protein?
Proteins with another chemical group associated with their polypeptide chain[s].
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What is a globular protein?
In globular proteins the polypeptide chain is folded into a compact spherical shape. These proteins are soluble due to the hydrophilic side chains that project from the outside of the molecules and are therefore important in metabolic reactions.
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What is a fibrous protein?
Proteins that do not fold up into a ball shape but remain as long chains. Several polypeptide chains can be cross linked for additional strength. These insoluble proteins are important structural molecules. Keratin in hair and skin is an example.
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What is the structure of a cell membrane?
A phospholipid bilayer
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What is a phospholipid bilayer?
The phosphate heads attract other polar molecules like water (hydrophilic), Non polar fatty acid tails are hydrophobic. They form a layer.
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What is the fluid mosaic model?
The cell surface membrane contains proteins, cholesterol, glycoproteins and glycolipids.
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Is the fluid mosaic model fixed?
No it is fluid. Some proteins are fixed within the membrane, but other are not and can move around in the fluid phospholipid bilayer. That's what makes it fluid.
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Evidence for the fluid mosaic model
Electron micrograph - the phosphate heads are more electron dense and show up as the darker edges to the membrane, with the tails forming the lighter inner part of the sandwich. Another was by fusing mouse and human cells together. Proves fluidity.
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Evidence for the integral membrane proteins
Free-fracture electron microscopy studies. Frozen membrane sections were fractured along the weak point between the lipid layers, and the inner fractured surface coated in heavy metal.
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When the mouse and human membrane protein experiment was carried out at 15', mixing was much slower. How does this evidence further support the fluid mosaic model of membrane structure?
Slower mixing at lower temperatures supports the model because movement of molecules in fluids is slower at lower temperatures.
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The more phospholipids containing unsaturated fatty acids there are present in the membrane, the more or less fluid it is?
More - The kinks in the hydrocarbon tails of the unsaturated phospholipids prevent them from packing closely togeth, so more movement is possible. Cholesterol reduces the fluidity of the membrane by preventing movement of phospholipids.
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Can you suggest why the membrane is more fluid with unsaturated rather than saturated phospholipids making up the bilayer?
The kinks in the fatty acids prevent them lying very closely togeth; this created more space in which the molecules can move.
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What is the role of glycoproteins and glycolipids in the cell membrane?
These have important roles in cell to cell recognition and as receptors.
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Name 5 ways in which molecules and ions move across membranes:
Osmosis, diffusion, active transport, exocytosis, endocytosis.
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What is diffusion?
It is the net movement of molecules or ions from a region where they are at high concentration to a region of their lower concentration. Diffusion will contiue until equilibrium, when the substance is evenly distributed.It is passive transport.
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What is facilitated diffusion?
The crossing of the membrane with the aid of proteins. Particles diffuse through channel proteins that span the membrane. Some channels can be opened or closed depending on the presence or absence of a signal (gated channels)
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The proteins involved in facilitated diffusion:
Channel proteins and carrier proteins - Carrier proteins change shape when the ion binds to the active site. This allows the ion to cross the membrane. Molecules can more from high or low concentrations.
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What is osmosis?
The net movement of water molecules from a solution with lower concentration of solute to a solution with a higher concentration of solute through a partially permeable membrane.
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Why is osmosis caused?
Osmosis is due to the random movement of water molecules across the membrane and is a praticular type of diffusion. If solute is present, H2O forms hydrogen bonds with them, reducing the movement. If more solute is present, fewer H2O free to collide.
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What is active transport?
Substances need to be moved across a membrane against a concentration gradient then energy (ATP) is required. Carrier proteins are also needed. The substance binds to the carrier protein, energy from ATP changes the shape, substance passes across.
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What is exocytosis?
When large molecules need to be transported across cell surface membrane. Exoctosis is the release of a substance from cell vesicles.
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What is endocytosis?
When large molecules need to be transported across cell surface membrane. Substances are taken into a cell by the creation of a vesicle. Part of the membrane engulfs the solid to be transported.
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What is the type of transport to be involved in movement of oxygen across the wall of an alveolus?
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What is the type of transport to be involved in absorption of phosphate ions into root hair cells?
Active transport
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What is the type of transport to be involved in pumping of calcium ions into storage vesicles inside muscle cells?
Active transport
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What is the type of transport to be involved in release of glucose from liver cells into the blood stream?
Facilitated diffusion/ channel protein
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What is the type of transport to be involved in removal of the sodium ions that diffuse into a nerve cell, thus maintaining a low concentration within the nerve axon?
Active transport
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What is the type of transport to be involved in reabsorption of water molecules from the kidney tubule?
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Regulating excess water in the mucus:
Na+ actively pumped across the basal membrane. Na+ diffuses through sodium channels in the apical membrane. Cl- diffuses down electrical gradient. Water is drawn out of cell by osmosis due to high salt concentration in TF. Water drawn out of mucus.
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Regulating too little water in the mucus:
Cl- pumped into the cell across basal membrane. Cl- diffuses through the open CFTR channels. Na+ diffuses down the electrical gradient into the mucus. Elevated salt concentration in the mucus draws water out of the cell by osmosis. Water goes in cell
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Regulation of mucus in people with CF:
CFTR channel is absent or not functional. Na+ is permanently open. Water is continually removed from mucus by osmosis.
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What is the effect of CF on the digestive system?
In a person with CF, the pancreatic duct becomes blocked by sticky mucus, imparing the release of digestive enzymes. The lower concentration of enzymes within the small intestine reduces the rate of digestion so nutrients are absorbed.
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What are enzymes?
Biological catalysts - they speed up chemical reactions that would otherwise occur very slowly at the temperatures within cells.
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What is the structure of an enzyme?
A precise 3D shape that includes a depression on the surface of the molecule called the active site.
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What is the lock and key theory?
A molecule with a completmentary shape, or a couple that together make a complementary shape, fit into the active site. The substrate molecules form temporary bonds with the amino acids of the active site to produce enzyme substrate complex.
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What is the enzyme substrate complex?
When the enzyme holds the substrate molecule in a way that they react more easily. When the reaction has taken place, they are released, leaving the enzyme unchanged.
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What is the induced fit theory?
Often the active site is flexible. When the substrate enters the active site, the enxyme molecule changes shape slightly, fitting more closely around the substrate. The enzyme can then return to its previous shape. Only a specific substance will work
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What is activation energy?
The energy needed to break bonds and start a reaction.
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How do enzymes reduce the activation energy?
The shape of the enzyme's active site and of it's substrate is such that electrically charged groups on their surfaces interact. The attraction of oppositely charged groups may distort the shape of the substrate and assist in the breaking of new bond
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The 5 main points about enzymes:
They are globular proteins. Have an active site that allows binding with specific substrate. Catalyse reactions. Reduce the activation energy required for chemical reactions. Remain unchanged at the end and are re-usable.
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How is the rate of reaction measures?
It is measured by determining the quantity of substrate used or the quanitity of product promed in a given time.
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What is the effect of CF on the reproductive system?
Females have redued chance of becoming pregnant because a mucus plug develops in the cervix. This stops sperm from reaching the egg. Males lack the vas deferens, meaning that sperm cannot leave the testes. If they have it, it is blocked.
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Unusually salty sweat is often one of the first signs that a baby may have CF. Why might the sweat of a person with CF be more salty than normal?
Salt is normally reabsorbed from sweat using the CFTR channel; with CF this does not function, so the salt is not absorbed making saltier sweat.
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What is CF caused by?
A mutation in the DNA that carries the instructions for making the CFTR protein.
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Where is DNA found?
In every cell nucleus
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What is DNA?
Deoxyribonucleic acid - It contains the genetic code which makes up an organism. It is a chain of nucleotides.
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What is a gene?
A sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chian. Each chromosome found in the cell nucleus contains a large amount of DNA and carries numerous genes.
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What makes a mononucleotide?
Phosphate group, deoxyribose and an organic base containing nitrogen.
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Which reaction joins the three molecules in a nucleotide together?
A condensation reaction between the sugar of one nucleotide and the phosphate of the next one, producing a long chain of nucleotides (a polynucleotide).
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What are the 4 organic bases?
Thymine, Adenine, Guanine, Cytosine
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How many strands of nucleotides are there in DNA?
There are two long strands that form a double helix. The sugars and phosphates form the back bone of the molecule and a joined by phosphodiester bonds.
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What type of bond joins together the nucleotide strands?
Hydrogen bonds between the pairs of bases.
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Why do the bases pair up?
Bases A and G both have a two-ring structure, whereas C and T have only one ring. The bases pair so that there are effectively three rings forming each 'rung' of the DNA molecule, making the molecule a uniform width along its whole length.
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What are the complementary base pairs in DNA?
C + G, A + T
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What is a triplet code?
In the genetic code, one base does not simply code for one amino acid. There are only four bases, so if this were the case proteins could contain only four different amino acids, instead of the 20 amino acids found commonly in proteins.
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A copy of DNA is not made using DNA, what is it made from?
Ribonucleic acid, RNA. The RNA can leave the nucleus, carrying the information to the cytoplasm where it is used in the manufacture of proteins.
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What are the key differences between DNA and RNA?
RNA has a single strand of RNA nucleotides. These are very similar in structure of DNA nucleotides but they contain ribose sugar, rather than deoxyribose. In RNA, the base uracil replaces thymin, so RNA never contains thymine.
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What are the stages of protein synthesis?
Transcription and Translation
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Where does the first stage of protein synthesis take place?
In the nucleus.
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Describe the process of the first stage of protein synthesis:
DNA double helix unwinds and hydrogen bonds between bases break. mRNA is built from free RNA nucleotides which line up aginst the DNA template strand. Becuase of complementary base pairing the DNA bases determines the mRNA bases.
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What happens to the mRNA strand after transcription?
It leaves the nucleus through a pore in the nuclear envelope and enters the cytoplasm.
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Where does the second stage of protein synthesis take place?
On ribosomes. They are small organelles made of ribosomal RNA and protein. They are found free in the cytoplasm or on the endoplasmic reticulum.
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What happens during translation?
The mRNA attaches to the ribosome. A tRNA molecule carrying an amino acid molecule has three bases called anticodon and these pair with complementary bases on the mRNA codon. The amino acids that the tRNA carry joing by means of peptide bonds.
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What is the bond formed between the amino acids?
Peptide bonds
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What happens when a cell divides?
An exact copy of the cell's DNA is produced so that each of the daughter cells recieves a copy. This is called replication.
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What is the process of DNA replication?
The DNA double helix unwinds from one end and the two strands split apart as the hydrogen bonds between the bases break. Free nucleotides line up alongside each DNA strand and hydrogen bonds form between the complementary bases.
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What is semi-conservative replication?
Each DNA molecule contains one original parent strand and one "new strand"
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What is conservative replication?
One DNA molecule has two original parent DNA strands, the other molecule has two "new" strands.
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What is fragmentary replication?
All DNA strands are made up of a mixture of original parent DNA nucleotides and new nucleotides.
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How did Meselson and Stahl determine that DNA replication is semi-conservative?
They did this using light and heavy strands of DNA.
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How does CF occur?
If a mutation occurs within a gene and a new base triplet is created that codes for a stop signal or different amino acid, then protein may be faulty. This could result in CF.
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What is the mutation that causes sickle cell anaemia?
The bases adenine replaces thymine at one position along the chain. The mRNA produced from this DNA contains the triplet code GUA rather than GAA. As a result the protein produced contains different amino acids and the haemoglobin is less soluble.
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Every cell (except sex cells) contains ... copies of each gene:
2 - One from each parent.
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What is the locus?
The positioning of the two copies of a gene
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What is a homologous chromosome?
A homologous pair is a pair of chromosomes containing a maternal and paternal chromatid joined to together at the centromere.
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What is an allele?
Different forms of the same gene.
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What is a genotype?
It is the alleles that make up a person's genetic make up
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What is your phenotype?
It is the characteristic caused by the genotype, the observable effect.
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What is monohybrid inheritance?
When the phenotype is controlled by one gene.
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What are the treatments for CF?
Medication, diet, digestive enzyme supplements, physiotherapy, heart and lung transplant
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What are the common medications to relieve the symptoms of CF?
Antibiotics (used to kill or prevent growth of bacteria in the lungs), DNAase enzymes (Can be inhaled using a neuliser, they break down the DNA, so the mucus is easier to clear from the lungs.) Bronchodilators (relax the muscles in the airways).
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What is the adivsed diet for people with CF?
High energy foods and their diet should double the quantity of protein recommended for people who do not have CF. Sometimes salt supplements are needed.
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How doese physiotherapy help people with CF?
Rhymical tapping of the walls of the chest cavity can help loosen the mucus and improve the flow of air into and out of the lungs.
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What is a possible CF treatment for the future?
Gene therapy. It would treat the cause rather than the symptoms.
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The process of gene therapy:
Normal alleles of the gene are inserted into the target cells, either using genetically modified virus to infect the target cells, or with liposomes. The normal form of the gene is transcribed and translated.Functioning protein is made in target cell
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How are genes inserted using viruses?
In a virus, the DNA sequence that allows replication is removed. It's replaced with the normal allele of the desired gene, with a promoter sequence that initiates transcription and translation of the gene. The viral DNA is incorporated into our DNA
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How are genes inserted using liposomes?
A copy of the normal allele is inserted into a loop of DNA (plasmid). The plasmids are combined with liposomes. The positively charged head groups of the phospholipids combine with the DNA to form a liposome DNA complex. The CF patient breathes it in
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What are somatic cells?
Body cells
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What are germ cells?
Sperm or eggs (Sex cells)
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What is germ line therapy?
Altering the germ cell so every cell in the body contains a new gene.
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Why are there ethical objections to germ lien therapy?
There are concerns about possible effects in future generations when the new gene is inherited.
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What is genetic testing?
The study of a person's DNA in order to identify genetic differences or susceptibility to particular diseases or abnormalities. This can be done using cheek cells, embryo cells or white blood cells.
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How can genetic testing be used?
To confirm a diagnosis, to identify carriers, for testing embryos, Testing before implantation
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How can genetic testing be used to identify carriers?
A sample of blood or cells taken from inside the mouth can be used to detect abnormal alleles in people without the disease who are heterozygous.
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How can genetic testing be used for testing embryos?
There are two techniques. Amniocentesis (inserting a needle into the amniotic fluid to collect cells) or CVS (a small sample of placental tissue is removed).
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What is amniocentesis?
A needle is inserted into the amniotic fluid to collect cells that have fallen off the placenta. This can be carried out at 15-17 weeks of pregnancy, and involves a risk of between 0.5% - 1%.
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What is CVS?
Chorionic villius sampling - a sample of placental tissue is removed, either through the wall of the abdomen or through thr ******. This can be carried out between 8 - 12 weeks, since there is no need to wait for amniotic fluid to develop. Risk =1/2%
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What are the implication of testing embryos?
Both procedures present a risk of miscarriage to a potentially health foetus. If the result is positive for a condition, women may be more inclined to abort the child.
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What is PIGD?
Pre-implantation genetic diagnoisis. When carrying ot in vitro fertilisation, it is possible to test an embryo before it has implanted in the uterus. It is expensive and fairly unreliable though, but avoids the need for a possible abortion.
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What are the ethical frameworks?
Rights and duties, Maximising the amount of good in the world, making decisions for yourself, leading a virtuous life.
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What is the rights and duties belief?
There are certain human rights that should always be permitted, e.g. the right to life.
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What is maxmising the amount of good in the world?
This is known as utilitarianism. Utilitarians have no moral absolutes beyond maximising the amount of good in the world. A utilitarian would hesitate to state that anything is always right or wrong.
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What is making decisions for yourself?
This is informed consent and the belief that you should do what's best for you in thel ong run.
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What is leading a virtuous life?
Considering the virtues that you might wish a good teacher to have. E.g. justice, prudence, temperance, fortitude, faith, hope and charity.
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What is a genetic counsellor?
A person who will help the couple understand how disease is inherited and the chance that any child they conceive will have it. A genetic counsellor will explain the tests available and the possible courses of action. They help in big decisions.
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Card 2


The mucus is continually removed by...


The wave like beating of cilia that cover the epithelial cells, lining the tubes of the gas exchange system.

Card 3


Why is the mucus of people with CF different?


Preview of the front of card 3

Card 4


The sticky mucus in the lungs has two major effects on health, these are:


Preview of the front of card 4

Card 5


What are epithelial cells?


Preview of the front of card 5
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