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Benedicts test

  • heat sample with benedicts reagent.
  • if the sample stays blue no reducing sugar is present.
  • if sample forms green, yellow, orange, brick red precipate reducing suagr is present.
  • heat sample with dilute HCl and neutralise sample by adding sodium hydrogencarbonate and heat sample with benedicts reagent.
  • if sample stays blue no non-reducing or reducing sugar present.
  • if sample forms, green, yellow, orange, brick red precipate non-reducing sugar present
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Emulsion test

  • shake substance with ethanol for about a minute.
  • pour solution into water.
  • any lipid will show up as a milky emulsion.
  • The more lipid there is the more noticeable the milky colour will be.
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Biuret test

  • add sodium hydroxide to make test solution alkaline.
  • add copper (II) sulfate solution.
  • if protein present solution turns purple 
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Iodine test

  • add iodine dissolved in potassium iodide solution to the test sample.
  • if starch  is present sample will go from browny-orange to dark blue-black colour.
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Lock and key model

  • substrate fits into the enzyme the same way a key fits into a lock.
  • the active site and substrate have a complementary shape.
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Induced fit model

  • Substrate doesnt have to be the perfect shape to fit into the active site.
  • it has to make the active site change shape slightly.
  • This locks the substrate even more tightly into the enzyme.
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DNA replication

  • DNA helicase breaks the hydrogen bonds between the bases on the polynucleotide strands which makes the helix unwind to form two single strands.
  • Each original strand acts as a template for a new strand.
  • Complementary base pairing happens so free floating nucleotides are attracted to their complementary exposed base.
  • Condensation reactions join the nucleotides of the strands together catalysed by DNA polymerase.
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Meselson and Stahl

  • Two samples of bacteria grown for many generations.
  • One in light nitrogen and one in heavy nitrogen.
  • As the bacteria reproduced it took up nitrogen from the broth to make nucleotides for DNA.
  • Sample of DNA was taken from the batch of bacteria and spun in a centrifuge, the heavy DNA settled lower than the light DNA.
  • Bacteria grown in heavy nitrogen was taken out and put in a brough containing only light nitrogen and was left for one round of DNA replication.
  • The DNA settled in the middle showing that the DNA contained a mixture of heavy and light nitrogen, proof that DNA replication is semi-conservative.
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Making and using ATP

  • When energy is needed ATP is broken down into ADP and Pi.
  • This is a hydrolysis reaction.
  • A phosphate bond is broken and energy is released.
  • The reaction is catalysed by ATP hydrolyse.
  • Pi can be added to other compounds to make them more reactive-phosphorylation.
  • ATP is resynthesised by condensation reactions between ADP and Pi.
  • Happens in respiration and photosynthesis.
  • Catalysed by ATP Synthase.
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Binary Fission

  • Circular DNA and plasmids replicate, DNA loop replicate once, plasmids as much as they want.
  • The cell size increases and DNA moves to opposite poles.
  • Cytoplasm begins to divide and new cell wall forms.
  • Cytoplasm divides and two daughter cells are produced.
  • Each daughter cell has one copy of the circular DNA but have a variable number of plasmids.
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Viral Replication

  • Virus attaches to host cell receptor proteins.
  • Genetic material is released into the host cell.
  • Genetic material and proteins are replicated by host cell 'machinery'.
  • Viral components assemble.
  • Replicated virusues released from host cell.
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Cell fractionation

  • Homogenisation: cells get grinded up in a homgenizer to break up the plasma and release the organelles into a solution. 
  • The solution must be kept ice cold to reduce enzyme activity.
  • Solution should be isotonic to prevent damage to the organelles through osmosis.
  • A buffer solution added to maintain the pH.
  • Filteration: homogenised cell solution is filtered through a gauze to separate large cell debris or tissue debris eg connective tissue. Organelles are smaller than debris so pass through gauze.
  • Ultracentrifugation: cell fragments poured into a tube, tube put into centrifuge, heaviest organelles flung to the bottom of the tube by a centrifuge and form a pellet, rest are the supernatant.
  • Supernatant is drained off and poured into another tube and the process starts again with the second heaviest organelle forming a pellet.
  • Each time the process is repeated the speed increases.
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The Cell Cycle

  • Mitosis, where the cell cycle starts and ends.
  • G1, gap phase 1 where the cell grows and new organelles and proteins are made.
  • Synthesis, cell replicates its DNA ready to divide by mitosis.
  • G2, gap phase 2 where cell keeps growing and proteins needed for cell divison are made.
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  • Prophase: Chromosomes condense, centrioles move to opposite poles forming spindle, nuclear envelope breaks down and chromosomes are free in the cytoplasm.
  • Metaphase: Chromosomes line up in the along the middle of the cell and become attached to the spindle by their centromere.
  • Anaphase: The chromosomes are pulled appart to opposite poles, centromere first, when the spindle contracts.
  • Telophase: Chromosomes uncoil and become long and thin again. Nuclear envelope forms around each group of chromosomes, there are now two nuclei.
  • Cytokinesis: Cytoplasm divides and two genetically identical daughter cells are produced.
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Temperature and Membranes

  • Below 0: Phospholipids dont have much energy, so cant move as much, closely packed together and membrane is ridgid, chanel and carrier proteins in the membrane denature and permeability of the membrane increases. Ice crystals may form and pierce through the membrane making it highly permeable when it thraws.
  • Between 0 and 45: Phospholipids can move around and arent that closely packed together, membrane partially permeable. As temperature increases phospholipids move aroud more because they have more energy, this also increases the permeability of the membrane.
  • Temperatures above 45: Bilayer begins to melt down and membrane becomes permeable. Water inside the cell expands and puts pressure on he membrane. Chanel proteins and carrier proteins denature making the cell more permeable.
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Investigating Water Potential

  • Making serial dilutions: Make several solutions of different, known concentrations to test the cylinders in. Serial dilutions are when you create a set of dilutions that decrease in concentration by the same factor each time. Its uselful for when you need to make a very weak solution because it means you dont have to measure out very small volumes of liquid.
  • Measuring change in mass: By measuring weight of potatoes before and after being in the solution.
  • Producing a calibration curve: Plot percentage change in mass against the concentration of sucrose solution. The curve can be used to determine the water potential of the potato cells.
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Co-transport and the absorption of glucose

  • Sodium ions are actively transported out of the epithelial cells in the ileum, into the blood, by the sodium potassium pump.
  • This creates a concentration gradient as theres a higher concentration of sodium ions in the lumen than inside the cell.
  • This causes the sodium ions to diffuse from the luemen of the ileum into the epithelial cells, down the concentration gradient.
  • The co-transporter carries glucose into the cell with the sodium. As a result the concentration of glucose inside the cell increases.
  • Glucose diffuses out of the cell, into the blood, down the concentration gradient through a protein chanel by facilitated diffusion.
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  • Phagocyte recognises foriegn antigens on a pathogen.
  • Cytoplasm of the phagocyte moves around the pathogen and engulfs it.
  • The pathogen is contained in the phagocytic vacuole in the cytoplasm of the phagocyte.
  • A lysosome fuses with the phagocytic vacuole and breaks down the pathogen.
  • The phagocyte then presents the pathogens antigens and sticks the antogens opn its surface to activate other immune system cels. The phagocyte is acting as an antigen-presenting cell.
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T and B Cells

  • T-cells have receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes. This activates the T-cells.
  • Cytotixic T-cells kill abnormal and foriegn cells.
  • Helper T-cell release chemical signals and activate and simulate phagocytes. They also activate B-cells.
  • B-cells are covered with antibodies. Each B-cell has a different shaped antibody on its membrane so different ones bind to different shaped antigens.
  • When the antibody on the surface on the B-cell meets a complementary shaped antigen, it forms and antigen-antibody complex.
  • This and substances released from helper T-cells activate B-cells in clonal selection which makes activated B-cells divide into plasma cells.
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Antibody Production

  • Plasma cells, clones of B-cells, secrete lots of monoclonal antibodies that are specific to the antigen.
  • The monoclonal antibodies bind to the antigens on the surface of the pathogen and form antigen-antibody complexes.
  • Agglutination happens - pathogens become clumped together.
  • Phagocytes then bind to the antibodies and phagocytose many pathogens at once, which leads to the destruction of pathogens carrying this antigen in the body.
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Primary and secondary immune response

  • Antigen enters body for first time and activates the immune system.
  • Primary resposne is slow because there arent many B-cells that can make the anitbody needed to bind to it.
  • Eventually the body will produce enough of the right antibody needed to overcome the infection, meanwhile the infected person will show symptooms of the disease.
  • After being exposed to the antigen T and B cells produce memory cells which remain in the body for a long time.
  • Memory T-cells remember the specific antigen and recognise it the second time around whilst memory B-cells record the specific antibodies needed to bind to the antigen.
  • When the same pathogen enters the body again the immune system produces a quicker, stronger response. 
  • Clonal selection happens faster and memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T-cells are activated and divide into the correct type of T-cell to kill the cell carrying antigen.
  • Secondary response often gets rid of pathogen before symptoms show.
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  • Vaccines contain a free or attached to a dead or attenuated pathogen. They are injected or taken orally.
  • The antigen causes the body to produce memory cells against the particular pathogen without it causing disease.
  • This allows you to become immune without any symptoms.
  • Vaccines protect individuals that have them by reducing the occurance of the disease.
  • Vaccines also protect those who arent vaccinated because of herd immunity.
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Influenza antigenic variation

  • The vaccine changes every year because the antigens on the surface of influenza change shape and form new strands of the virus.
  • Memory cells produced from vaccinations with the old strain wont be able to recognise the new strains of the virus as they are immunologically distinct. So the immune system has to start from scratch and carry out the primary response against the new antigens.
  • The primary response takes time which is why you get ill again.
  • Every year there are new vaccinations developed and the one most effective against the new strand of influenza gets chosen.
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Monoclonal antibodies in anti-cancer drugs targete

  • Different cells in the body have different surface antigens.
  • Cancer cells have antigens called tumour markers and are not found on normal body cells.
  • Monoclonal antibodies can be made that bind to tumour markers.
  • Anti-cancer drugs can also be attached to the monoclonal antibodies.
  • When the antibodies come into contact with the cancer cells they will bind to the tumour markers.
  • This means that the drug will only accumulate in the body where there are cancer cells so the side effects on an antibody-based drug are lower than other drugs because they accumulate near specific cells.
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Monoclonal antibodies in pregnancy tests

  • The application area contains antibodies that are complemenary to the hCG protein bound to a coloured bead.
  • When urine is applied to the application area aby hCG will bind to the antibody on the beads and form an antigen-antibody complex.
  • The urine moves up the stick to the test.  carrying any beads with it.
  • The test contains antibodies to the hCG that are stuck in place.
  • If there is hCG present the test shows that the person is pregnant because the immobilised antibody binds to any hCG attached.
  • If no hCG present the beads pass through the area without binding to anythng so it wont show the person is pregnant.
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Direct ELISA

  • Uses a single antibody thats complementary to the antigen being tested.
  • Antigens from a patients sample are bound to the inside of a well in a well plate.
  • A detection antibody that is complementary to the antigen of interest is added.
  • If the antigen of interest is present in the patients sample it will be immobilised on the inside surface of the well and the detection antibody will bind to it.
  • The well is then washed out to remove any unbound antibody and a substrate solution is added.
  • If the detection antibody is present the enzyme reacts with the substrate to give a colour change.This is a positive result for the presence of the antigen.
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Indirect ELISA for HIV

  • HIV antigen is bound to the bottom of a well in a well plate and a sample of the patients blood is added to the well. Any HIV specific antibodies will bind to the HIV antigen stuck to the bottom of the well.
  • The well is then washed out to remove any unbound antibodies and a secondary antibody that has a specific enzyme attached to it is added to the well which can bind to the HIV-specific antibody.
  • The well is washed out again to remove any unbound secondary antibody. A solution is then added to the well which contains a substrate and is able to react with the enzyme attached to the secondary antibody and produce a coloured product.
  • If the solution changes colour it indicates that the patient has HIV-specific anibodies in their blood and are infected with HIV.
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HIV replication

  • Attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-cell.
  • The capsid is released into the cell where it uncoats and releases the genetic material into the cells cytoplasm.
  • Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template.
  • Double stranded DNA is made from the viral RNA and is then inserted into the human DNA.
  • Host cell enzymes are used to make viral proteins from viral DNA found within the human DNA.
  • The viral proteins are assembled into new viruses which bud from the cell and go on to infect other cells.
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Fish gas exchange

  • Water enters the fish and passes out through the gills which is made of lots of gill fillaments which give a large surface area for gas exchange.
  • Gill fillaments are covered in lots of tiny lamellae which increase the surface area even more, they have lots of blood capillaries and a thing surface layer of cells to speed up diffusion between water and blood.
  • In gills blood flows through in one direction and water flows over in the other. This creates a counter-current system and means that the water with a high concentration of oxygen flows past blood with a relatively low concentration of oxygen.
  • This steep concentration gradient is maintained between water and blood so oxygen diffuses into the blood from the water.
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Gas exchange in plants

  • Plants obtain the gases they need through their leaves. They require oxygen for respiration and carbon dioxide for photosynthesis.
  • The gases diffuse into the intercellular spaces of the leaf through pores, which are normally on the underside of the leaf - stomata. From these spaces they will diffuse into the cells that require them.
  • Stomatal opening and closing depends on changes in the turgor of the guard cells. When water flows into the guard cells by osmosis, their turgor increases and they expand. Due to the relatively inelastic inner wall, the guard cells bend and draw away from each other, so the pore opens. If the guard cells loose water the opposite happens and the pore closes. The guard cells lower their water potential to draw in water from the surrounding epidermal cells, by actively accumulating potassium ions. This requires energy in the form of ATP which, is supplied by the chloroplasts in the guard cells.
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Gas exchange in insects

  • Insects have no transport system so gases need to be transported directly to the respiring tissues.
  • There are tiny holes called spiracles along the side of the insect which are openings of small tubes running into the insect's body, the larger ones being called tracheae and the smaller ones being called tracheoles. Oxygen travels down the concentration gradient towards the cells.
  • The ends of these tubes, which are in contact with individual cells, contain a small amount of fluid in which the gases are dissolved. The fluid is drawn into the muscle tissue during exercise. This increases the surface area of air in contact with the cells. Gases diffuse in through the spiracles and down the tracheae and tracheoles.
  • Ventilation movements of the body during exercise may help this diffusion.
  • The spiracles can be closed by valves and may be surrounded by tiny hairs. These help keep humidity around the opening, ensure there is a lower concentration gradient of water vapour, and so less is lost from the insect by evaporation.
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Inspiration and expiration

  • Inspiration: External intercostal mucles and diaphragm mucles contract. Ribcage moves up and out increasing thoratic cavity volume and decreasing pressure as pressure in alveolar lung is less than atomospheric pressure. Air flows into the lungs along the pressure gradient.
  • Expiration: External intercostal muscles and diaphragm relax. Ribcage moves down and in and  volume of thoratic cavity decreases and pressure increases as pressure in alveolar lung is more than atmospheric so air flows out of the lung along the pressure gradient.
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movement of O2 and CO2 in gas exhange system

  • Air moves down the trachea, brochi and bronchioles into the alveoli down a pressure gradient. Oxygen then moves into the blood where it can be transported around the body.
  • Carbon dioxide moves down its own diffusion and pressure gradient but in the opposite direction to oxygen so it can be breathed out.
  • Oxygen diffuses out of the alveoli across the alveolar epithelium and the capillary endothelium and into haemoglobin.
  • Carbon dioxide diffuses into the alveoli from the blood.
  • Trachea - Bronchi - Bronchioles - Alveoli - Alveolar epithelium - Capillary endothelium - Blood.
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Digestion of Carbs

  • Amylase catalyses the breakdown of starch which is a mixture of amylopectin and amylose. Amylase catalyses the hydrolysis reaction that break the glycosidic bonds in starch to produce maltose. Its produced by the salivary glands which release amylase into the mouth and by the pancreas which release it into the small intestine.
  • Membrane-bound disaccharides are enzymes attached to the cell membranes of epithelial cells lining the ileum, they break down disaccharides into monosaccharides.
  • Maltose and lactose are broken down in similar ways to sucrose.
    • disaccharide - disaccharidase - monosaccharides
    • Sucrose - sucrase - glucose + fructose
    • Maltose - maltase - glucose + glucose
    • Lactose - lactase - glucose + galatose
  • The monosaccharies can be transported across the epithelial cell membranes in the ileum via specific transporter proteins.
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Digestion of lipids

  • Lipase enzymes catalyse the breakdownn of lipids into monoglycerides and fatty acids.
  • The ester bond is hydrolysed.
  • Lipase is mainly made in the pancreas and is secreated into the small intestine where they act.
  • Bile salts produced in the liver emulsify lipids - cause them to form small droplets.
  • Bile salts arent enzymes but are important because they help to increase the surface area of the lipid available for lipase to work on, as several small lipids have a larger surface area than one large droplet.
  • Once the lipids broken down by lipase the monoglycerides and fatty acids stick with the bile salts and form tiny structures called micelles which help the products of lipid digestion to be absorbed.
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Digestion of Proteins

  • Endopeptidases hydrolyse the peptide bond in the protein.
  • eg pepsin is released into the stomach by cells in the stomach lining and only works in acidic conditions which is provided by the HCl in the stomach.
  • Exopeptidases hydrolyse peptide bonds at end of proteins, they remove single amino acids from proteins.
  • Dipeptidases are exopeptidases that work specifically on dipeptidesand separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them. 
  • Theyre often located in the cell-surface membrane of epithelial cells in the small intestine.
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Absorption of products of digestion

  • Monosaccharides: Glucose is absorbed by active transport with sodium ions via a co-transporter protein. Galatose is absorbed in the same way using the same protein, frutose is absorbed via facilitated diffusion through a different protein.
  • Monoglycerides and fatty acids: Micelles help to movethe monoglycerides and fatty acids towards the epithelium, they can release monoglycerides and fatty acids allowing them to be absorbed. Monoglycerides and fatty acids are lipid-soluble so can diffuse directly across the epithelial cell membrane.
  • Amino Acids: Absorbed in a similar way to glucose and galatose. Sodium ions actively transporteed out of the epithelial cells into the ileum itself then diffuse back into the cell through a sodium-dependant transporter protein in the epithelial cell membrane and carry amino acids with them.
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Tissue fluid

  • Fluid that surrounds cells in tissues and is made of small molecules that leave the blood plasma, unlike blood it doesnt contain red blood cells or big protiens.
  • Cells take oxygen and nutrients from the tissue fluid and release metabolic waste into it. In a capillary bed substances move out of the capillaries and into the tissue fluid by pressure filteration.
  • At the start of the capillary bed the hydrostatic pressure inside the capillaries is higher than in the tissue fluid meaning that theres an overall outwards pressure that forces fluids out of the capillary and into the spaces around the cell, forming tissue fluids.
  • As fluid leaves the hydrostatic pressure reduces in the capillaries so hydrostatic pressure is lower in the venule end of the capillary bed.
  • Due to fluid loss and increasing plasma concentration water potential in the venule is lower than in the tissue fluid which means water re-enters the capillaries from the tissue fluid at the venule end by osmosis.
  • Any excess tissue fluid is drained into the lymphatic system which transports excess fluid from the tissues and passes it back into the circulatory sytem.
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