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136 Cards in this Set
- Front
- Back
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What is Correlation? |
When a change in one variable is reflected by a change in other variable. Correlations can be positive or negative. |
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How do you calculate percentage increase/decrease? |
Work out the difference between the two values and divide by the value you are comparing to (original value). |
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How do you test for reducing sugars (eg glucose)? |
Heat with Benedict's Reagent and there should be a colour change from blue to brick red. |
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How do you test for non-reducing sugars (eg sucrose)? |
Heat with Benedict's Reagent and there should be no colour change (stays blue). Then boil with dilute HCL and neutralise with NaHCO^3. Re-heat with Benedict's reagent and colour change from blue to brick red. |
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How do you test for Starch? |
Add iodine in potassium iodide solution and there should be a colour change from brown to blue-black. |
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How do you test for Protein? |
Add Biuret reagent to the sample and there should be a colour change to lilac. |
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How do you test for Lipids? |
Add ethanol and shake, then add water and shake. The solution should turn milky. |
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Describe how two monosaccharides are joined together. |
Condensation reaction with water formed when two OH (hydroxyl) groups join. |
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Describe the structure of Cellulose. |
Made of monomers of beta-glucose joined together by condensation reactions between hydroxyl groups. Every other beta-glucose is rotated 180 degrees. C1, 4 Glycosidic bonds Polymer chains are unbranched and joined together by numerous hydrogen bond cross bridges (these bonds give cellulose high tensile strength). Molecules are grouped together into microfibrils. |
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Describe the functions of the cellulose cell wall. |
To provide mechanical strength to prevent cell bursting under the pressure created by osmotic entry of water. To give strength to the plant for support. To allow water to pass along it and contribute to the movement of water through the plant. |
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Explain how the structure of cellulose is related to its role in plant cell walls. |
Long, straight (unbranched/linear) chains of beta glucose joined by hydrogen bonds to form microfibrils which provides rigidity/support/tensile strength. |
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Describe the structure of starch. |
Made of monomers of beat-glucose joined together by condensation reactions between hydroxyl groups. C1, 4 and C1, 6 glycosidic bonds. Amylose is helical (C1, 4 bonds only). Addition of C1, 6 bonds makes amylopectin, a branched molecule. |
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Describe the role of starch. |
Energy store in plant cells. Insoluble therefore does not affect the osmotic movement of water in and out of cells. Insoluble so does not easily diffuse out of cells - good for storage. Helical structure so compact. Branches mean that it is easily hydrolysed to form alpha-glucose , which can be transported. |
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Describe the structure of Glycogen. |
Made of monomers of beta-glucose joined together by condensation reactions between hydroxyl groups, C, 2 and C1, 6 glycosidic bonds. More C1, 6 bonds than starch so is more branched so more easily hydrolysed. Only found in liver and muscle cells of animals. |
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Describe the protein structure - hierarch of folding. |
1. Amino acids sequence in a polypeptide chain. 2. Polypeptide folds to have weak intermolecular forces between hydrogen bonds which hold it in shape. (Can be beta-pleated sheets or an alpha-helix). 3. Secondary structure further folds to form tertiary structure (globular or fibrous); forms shape that is specific to that protein only. 4. More than one polypeptide chain folds together (eg Haemoglobin) |
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What two types of tertiary structures are there? Give examples for each. |
Globular (chemical) - myoglobin and Fibrous (structural) - collagen |
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Why is the tertiary structure important? |
The 3D shape means a structure is specific and usually will have one substance which is complementary to the shapes. Some molecules are complementary to receptors. (eg Cholera protein). |
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What factor is important in the folding of the tertiary structure? |
The protein is entirely dependent on the primary sequence of amino acids; the number and type of amino acids and the order they're in is entirely responsible for causing the folding pattern and where the bonds form. |
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Describe the primary structure. |
1. Amino acids join together as primary structure by a condensation reaction forming peptide bonds (covalent) which occurs in the ribosome.
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Describe the secondary structure. |
2. Specific structures form during secondary folding - alpha-helix and beta-pleated sheet. Numerous hydrogen bonds form between O and H atoms, which stabilise the structure.
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Describe the tertiary structure. |
3. Secondary structure further folds to form specific tertiary structure (globular or fibrous) which are held together by ionic and disulphide bonds.
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Describe the quaternary structure. |
4. Quaternary structure is where more than one polypeptide chain folds together (eg Haemoglobin)
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What is activation energy? |
The minimum amount of energy required to bring particles in close contact so they will collide and react. |
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What are enzymes? |
Enzymes (protein molecules) are biological catalysts so they lower the activation energy. |
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Describe the Lock and Key theory. |
Enzymes have an active site with a specific shape that is rigid. The substrate that is a complementary shape binds to the active site. |
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Describe the Induced fit theory. |
The substrate is not as first complementary to the active site of the enzyme but upon binding the active site of the enzyme molds around the substrate so the substrate becomes complementary which forms an enzyme-substrate complex. This puts bonds in the substrate under strain which lowers the activation energy. |
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Why does increased temperature affect reaction rate? |
Particles have more kinetic energy therefore they move more so there are more collisions between substrates and active sites so more ES complexes form. |
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Explain what enzyme denaturation is. |
When temperature rises above the optimum temperature for enzymes, it breaks the hydrogen bonds which causes the tertiary structure to unfold. So the enzymes active site changes shape and the substrate can no longer bind to the active site, as it's no longer complementary. Therefore fewer ES complexes form. |
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Describe the effect of changes in pH on enzyme activity. |
Ionic bonds holding the tertiary structure break so the active site distorts and the substrate can no longer bind to the active site. Charges on the amino acids in the active site are affected so fewer ES complexes form. |
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Explain what a competitive enzyme inhibitor is. |
An inhibitor has a similar shape to the substrate so it binds competitively for the active site as it has a complementary shape. Fewer substrate molecules can bind to the active site therefore fewer ES complexes are formed but the effect can be overcome by adding more substrate. |
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Explain what a non-competitive inhibitor is. |
An inhibitor binds regulatory region away from the active site, the active site changes shape so the substrate can no longer bind as it is no longer complementary. Fewer ES complexes form but the effect can be overcome by adding more substrate. |
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What does DNA stand for? |
Deoxyribose Nucleic Acid |
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Describe DNA replication. |
Helicase unzips DNA's double helix by breaking hydrogen bonds. Free DNA nucleotides in the nucleus complementary base pair with exposed bases on both strands. Hydrogen bonds between complementary base pairs reform, both strands act as a template. DNA polymerase joins nucleotides together on the new strands by catalysing the formation of new phosphodiester bonds. This results in the formation of identical strands. |
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What is semi-conservative replication? |
Two new molecules are formed which are exact copies of the original. One of the chains in each new molecule was present in the original molecule. The other chain is newly synthesised from free nucleotides. |
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How does DNA structure relate to its function? |
Stable due to numerous hydrogen bonds so can be passed on from generation to generation. Hydrogen bonds between strands are easily broken for DNA replication or protein synthesis. Large so can carry lots of genetic information. Base pairs are contained within the helix and are protected from corruption and held in place by strong sugar-phosphate backbone. Complementary base pairs allow synthesis for an identical daughter molecule. Helical shape means it can be coiled so compact for storage. |
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What is a gene? |
A section of double-stranded DNA coding for a single polypeptide. |
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What is the triplet code? |
Three bases in a particular sequence code for one amino acid. |
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Describe the relationship between DNA and proteins. |
DNA has a specific sequence of bases arranged into specific codons (triplets). Each codon codes for one amino acid. The ribosome reads the code and arranges the amino acids in the correct order (determined by the DNA sequence). Peptide bonds form between amino acids making a polypeptide chain which is then folded to make a protein with a specific tertiary structure. |
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Explain how a change in DNA base sequence (a mutation) may result in the production of a non-functional enzyme. |
Changes DNA codons, Changes primary sequence of amino acids, Changes folding pattern in 2nd and 3rd structure, Changes position of hydrogen, ionic, and disulphide bonds, Changes shape of active site (affects tertiary structure), Substrate may no longer be complementary so ES complexes can no longer form. |
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What does ATP stand for? |
Adenosine Triphosphate |
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Describe the structure of DNA. |
Sugar (deoxyribose) with HO, phosphate and bases attached: Adenine Guanine Cytosine Thimine Complementary base pairings connected by hydrogen bonds. Helical shape (double helix) |
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What does RNA stand for? |
Ribose Nucleic Acid |
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What is the sugar in RNA called? |
Ribose |
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What is the sugar in DNA called? |
Deoxyribose |
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Describe the structure of RNA. |
Sugar (Ribose) with OH, phosphate and bases attached: Adenine Uracil Guanine Cytosine No complementary base pairings therefore no hydrogen bonds so less stable than DNA. Generally smaller than DNA. Linear molecule. |
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Describe the functions of RNA. |
Has a role in protein synthesis. Makes a copy pf DNA's genetic code in the nucleus. Travels out of the nucleus to the ribosome where the copy of the code then helps the ribosome to put the amino acids together in the correct sequence to produce the right shaped protein. |
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What is the chemical equation for ATP? |
ADP + Pi = ATP + H20 |
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Describe how ATP is adapted for its role as an energy transfer molecule. |
ATP is hydrolysed in a single step reaction releasing energy. ATP releases energy in small quantities. ATP is soluble. |
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Why do cells need to synthesise lots of ATP? |
ATP cannot be stored or transported. ATP is used for muscle contracted/active transport/cell division/DNA replication/protein synthesis. |
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Describe the flow of energy used in the process of ATP. |
1) Photosynthesis in producers converts light energy into chemical energy. 2) Respiration in all cells converts chemical energy (from glucose) into ATP. 3) Energy from the breakdown of ATP is used by cells to carry out useful functions. |
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Describe the breakdown of ATP. |
Immediate source of energy due to unstable bonds. ATP is broken down by a hydrolysis reaction into ADP. Energy is released due to this breakdown. ATP + Water = ADP + Inorganic + Energy Phosphate |
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What is the role of enzymes in ATP? |
The breakdown of ATP can be catalysed by ATP hydrase. The synthesis of ATP can be catalysed by ATP synthase. |
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What is Specific Heat Capacity? |
The energy taken to heat 1kg of water by 1 degree Celsius. |
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Why does water have a specific heat capacity? |
It requires lots of heat energy to break the hydrogen bonds between molecules. Acts as a buffer against temperature variations in the atmosphere, aquatic environments and at a cellular level. Causes stability in terms of temperature. |
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What is Latent heat of vapourisation? |
The energy needed to evaporate 1g of water. |
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Why does water have a latent heat of vapourisation? |
Hydrogen bonding between water molecules which means that a lot of energy is required to evaporate it. This is useful as a cooling mechanism for animals, eg, evaporation of sweat or evaporation of saliva during panting. |
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What is the polarity of water? |
Shared electrons (covalent bonding) due to hydrogen having a slightly positive end (pole) and oxygen has a slightly negative end (pole) so the oppositely charged poles attract and form a covalent bond. No charge overall. |
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Why is water important to living organisms? |
Water in metabolism; water is used to break down many complex molecules by hydrolysis reactions (most chemical reactions also take place in an aqueous medium). Water is also needed during the first stage of photosynthesis. Water as a solvent; substances can readily dissolve in water such as gases, waste products (ammonia and urea), inorganic ions, amino acids monosaccharides and enzymes. This aids in cell transport. Evaporation of water is a cooling mechanism for some organisms. Water is not easily compressed and therefore it provides support (eg, turgidity in plant cells). It is transparent and therefore light can penetrate. |
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What is Adhesion? |
Where water molecules stick to something else (eg, the sides of xylem vessels). |
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What is Cohesion? |
Where water molecules 'stick together' by means of hydrogen bonding. |
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Why is cohesion useful in plants? |
Water is drawn up xylem vessels. |
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What is surface tension? |
Where water molecules meet air and they tend to be pulled back to the body of water. |
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Why is surface tension important for small organisms? |
Surface tension is strong enough to support them. |
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How are prokaryotes different from eukaryotes? |
Prokaryotes: have circular DNA, don't have membrane bond organelles, have smaller 70's ribosomes, have a capsule may have flagellum or a single flagella have plasmids have a cell wall made of murein |
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How are eukaryotes different from prokaryotes? |
Eukaryotes: have linear DNA have membrane bound organelles have larger 80's ribosomes do not have a capsule do not tend to have flagella but may have cillia or microvilli do not have plasmids have a cell wall made of cellulose |
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How are animal cells different from plant cells? |
No chloroplasts/chlorophyll No cell wall Generally animal cells are smaller than plant cells Animal cells are less regular in shape Have lysosomes Fewer and larger Golgi bodies No starch grains |
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How are plant cells different from animal cells? |
Contain chloroplasts and chlorophyll to absorb light for photosynthesis Cell wall made of cellulose General size is larger than animal cells More regular in shape (usually cuboidal or rectangular) No lysosomes More smaller Golgi bodies Starch grains may be present Usually have a large vacuole |
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How does bacteria replicate? |
Circular DNA replicates - both copies attach to the cell membrane. Plasmids also replicate. Cell membrane begins to grow between the two DNA molecules and pinches inward, dividing the cytoplasm in two. A new cell wall forms between the DNA molecules. Each new cell has an identical copy of the circular DNA molecule but a variable number of the plasmids. |
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How do viruses replicate? |
Virus attaches to host cell surface using an attachment protein. Viral DNA is injected inside the host cell. DNA is replicated inside the host cell. Carrying the genes coding for a new protein coat (capsid). New capsids are synthesised by host cell ribosomes. New viruses are assembled by the host cell. Host cell ruptures releasing mature viruses. |
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Describe the cell adaptations and functions of intestinal epithelial cells. |
Function - secrete digestive enzymes and aid absorption of nutrients from lumen of small intestine to blood. They can do this because: - many mitochondria to produce ATP in respiration, active transport and protein synthesis, - microvilli increase its surface area for absorption, - many ribosomes/lots of RER to produce digestive enzymes. |
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Describe the cell adaptions and functions of phagocytes. |
Function - a type of white blood cell involved in an immune response called phagocytosis where the white blood cell engulfs the pathogen and destroys it. They can do this because: - many lysosomes, containing hydrolytic enzymes - many ribosome's/lots of RER to synthesise the enzymes. |
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Describe the cell adaptions and functions of sperm cells.
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Function - gametes (sex cells) produced by male organisms that fuse with female gametes during fertilisation. They can do this because: - tail for movement - lots of mitochondria to create ATP so lot of energy for movement - enzymes in head allow it to penetrate the egg - haploid nucleus for fertilisation. |
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Describe the cell adaptions and functions of Pancreatic cells.
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Function - to secrete hormones that control blood glucose levels and to secrete enzymes such as amylase involved in digestion. They can do this because: - lots of ribosomes/RER to synthesise enzymes and hormones - larger Golgi bodies to aid packaging and vesicle production - lots of SER to process lipids to make hormones lots of mitochondria to create ATP so energy for protein synthesis and secretion. |
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Describe the cell adaptations and functions of leaf palisade cells. |
Function - to absorb light for photosynthesis to make glucose for the plant. They can do this because: - large vacuole so cells are turgid and pushes chloroplasts to the edges of the cell to maximise light absorption - numerous chloroplasts for photosynthesis - rectangular shape and closely packed together. |
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Name the limitations of optical microscopes. |
Resolution is too poor. Wavelength of light is too long. |
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Name the advantages of optical microscopes. |
Can view living cells. Can view movement. Smaller and more mobile so can be used in the field. Slide preparation (fixation) is easier, faster and cheaper. No vacuum required. |
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Why are electron microscopes better for viewing smaller objects? |
Resolution is higher as electrons have a shorter wavelength than light. |
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What are the principles of an electron microscope? |
Electrons are fired at a sample; the more dense material absorbs more electrons so it appears darker on the image. |
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What are the limitations of electron microscopes? |
Living cells cannot be seen. Carried out in a vacuum therefore expensive. Specimen had to be very thin. Artefacts may be produced in the image. |
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What are the advantages of electron microscopes? |
Smaller objects can be seen. High resolution as wavelengths are shorter than light wavelengths. Objects inside the cell can be viewed. |
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Why does different slices from the same tissue sample or cell give different organelles in the image? |
Sample has to be cut very thin during preparation. Different images have been viewed from different planes. |
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Why is an ice-cold isotonic buffer solution used in cell fractionation? |
Ice-cold - to slow down enzyme activity or prevent self-digestion by enzymes in lysosomes. Isotonic - to prevent water movement by osmosis. Buffer solution - to prevent changes in pH that may affect protein structure or denature membrane proteins in organelles. |
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Why is tissue homogenised? |
To release cell contents (organelles). |
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How are mitochondria isolated in cell fractionation? |
Tissue is homogenised in an ice cold, isotonic, buffer solution. Solution is filtered to remove cell debris and then then the solution is spun at a low speed in an ultracentrifuge. Heavy organelles (eg, nuclei) are removed from the sediment. Supernatant (containing suspended mitochondria) is spun at a faster speed for longer to isolate lighter (less dense) organelles. |
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How do you calculate the size of organelles given the magnification? |
Measure the organelle in mm and convert to macrometres (x1000) or nanometres (x1,000,000). Divide by the magnification. |
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How can you estimate the size of a cell/organelle when given no figures? |
Measure the length of objects with an eyepiece scale. Calibrate against something of known and uniform length eg red blood cells. |
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Describe the phospholipid bilayer. |
Phosphate head groups are hydrophillic, they point outwards because they interact with water (cytoplasm and tissue fluid). Fatty acid tails are hydrophobic, they point inwards because they repel water. |
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Explain why the model for membrane structure is known as the fluid mosaic model. |
Fluid - the membrane has movement due to cholesterol; it is semi-liquid. Mosaic - the proteins are distributed throughout the membrane unevenly and in a mosaic pattern. Model - The agreed structure is based upon experimental and chemical evidence and is classed as a model. |
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What types of proteins can be found in the plasma membrane? |
Peripheral or extrinsic are on the outside of the membrane. Integral proteins are running though the membrane. |
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What are the roles of membrane proteins? |
Receptors (tend to be glycoproteins), Antigens (tend to be glycoproteins), Enzymes, Ion channels (integral), Carrier proteins, Some membrane proteins also have a role in anchoring the cell and in cell signalling (sending messages to other cells). |
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What is diffusion? |
The net movement of solutes from a high to a low concentration down the concentration gradient across a partially permeable membrane. It does not need ATP (passive). |
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What features do particles need to diffuse passively? |
Small, Lipid soluble, Non-polar (uncharged). |
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What is facilitated diffusion? |
Net movement of solutes from a high to a low concentration down a concentration gradient which does not need ATP (passive). Charged particles pass through ion channels, large particles are carried by carrier proteins. |
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What is active transport? |
Net movement of molecules against a concentration gradient from an area of low to high concentration. Requires energy in the form of ATP (as well as carrier proteins) to move particles against a gradient. |
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Why do some cells have lots of mitochondria? |
Mitochondria produce ATP by respiration; energy released is used to carry substances against a concentration gradient. |
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What is Frick's Law? |
The rate of diffusion is proportional to (surface area x concentration gradient) divided by thickness. |
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What is osmosis? |
Net movement of water from a high to a low water potential across a partially permeable membrane. |
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How do you find the water potential of the same value as the tissue used? (eg, potato) |
Plot a graph of results, draw a line of best fit. Extrapolate the data to find the concentration where the ratio is 1 or there is no change in mass. |
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What is the longest part of the whole cell cycle? |
Interphase |
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Describe interphase. |
Before a cell can reproduce, it has to perform a variety of activities to get ready. While preparing to reproduce, the cell makes more cytoplasm. When it's ready, it goes through three sub-phases of interphase: G1(protein synthesis), S (DNA replication) G2 (build up of ATP). |
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Describe prophase, metaphase, anaphase, telophase and cytokinesis. |
Prophase - chromosomes condense (shorter and fatter); nuclear envelope disappears; spindle (protein fibres) forms in cell. Metaphase - chromosomes line up on equator of spindle; spindle fibres attach to chromosomes at the centromere. Anaphase - spindle fibres contract and pull sister chromatids towards opposite poles of the cell. Telophase - new nuclear envelope forms; chromosomes uncoil. Cytokinesis - cytoplasm divides and new cell membrane forms. |
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Why do we use a root tip end, orcein stain and squash the sample when we preform the root tip squash practical? |
Root tip end - has fast growing cells, dividing by mitosis. Lacto-propionic orcein stain - makes chromosomes visible. Squashed - to get think tissue layer letting enough light through for the optical microscope. |
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What is cancer? |
Rapid and uncontrollable division by mitosis. |
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How do some drug treatments prevent cancer? |
Some drugs treat cancer by preventing DNA replication, others work by preventing the spindle fibres from attaching. Either way cell division is inhibited therefore cell division slows down so the tumour growth also slows down. |
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What is a tissue? |
A group of similar cells organised to carry out a specific function. |
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What is an organ? |
A combination of tissues that are coordinated to preform a variety of functions. |
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What is cell differentiation? |
The process of a cell becoming specialised in structure to carry out a specific role. |
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How do pathogens cause disease? |
Produce toxins, Replicates inside host cell, Causing damage to cells and tissue. |
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What is an antigen? |
Protein molecule that causes T or B cell production/antibody production. |
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What are the differences between specific and non-specific response? |
Non-specific mechanisms do not distinguish between one type of pathogen and another but respond in the same way; eg, barrier to entry o pathogens or phagocytosis. Specific mechanisms distinguish between different pathogens and provide longer lasting immunity; eg, cell-mediated response involving T-lymphocytes or humoral response involving B-lymphocytes. |
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Name 3 barriers to pathogen entry. |
Protective covering the body (eg, skin). Epithelia are covered in mucus. Hydrochloric acid in the stomach. |
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What is the difference between B-cells and T-cells? |
B-cells mature in the bone marrow. T-cells mature in the thymus gland. |
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Describe Phagocytosis. |
Chemical products of the pathogen act as attractants, causing phagocytes ti move towards the pathogen. Phagocytes attach themselves to the pathogen surface. Phagocytes engulf pathogen to form pathogen to form a phagosome. Lysosomes move towards the vesicle and fuse with it to form a phagolysosome. Digestive enzymes within the lysosome break down the pathogen by hydrolysis. Soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte. |
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Describe cell-mediated immunity. |
Pathogens are taken in by antigen presenting cells eg, phagocytes Antigen presenting cell presents antigens from the pathogen on its cell surface membrane. Receptors on certain T-helper cells fit exactly onto these antigens- they are complementary. This activates other T-cells to divide rapidly by mitosis and form a clone. Some cloned T-cells then develop into memory cells. Some differentiate into killer T-cells which can perforate the infected cell membrane, killing the cell and pathogen. |
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Describe humoral immunity. |
Surface antigens of invading pathogen are taken up by B-cells eg, macrophages B-cells process the the non-self antigens and display them on their own cell surface membrane (antigen presentation). T-helper cells attach to the processed antigens on the B-cells and activate them. B-cells are activated to divide by mitosis to produce plasma cells clones. Cloned plasma cells produce antibodies complementary to antigens on the pathogen's surface. Antibodies attach to antigens and destroy the pathogen (primary response). Some B-cells develop into memory cells and can respond to future infections (secondary response). |
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Why do antigens vary in shape and size? |
Some pathogens have different strains - their antigens keep changing shape. Usually due to mutation in the pathogen DNA. Shape of antigens does not correspond to antibodies formed in previous infections (not complementary). Therefore no appropriate memory cells to stimulate antibody production and no antigen-antibody complexes can form. |
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What are the features of the secondary immune response (compared to primary)? |
Antibodies are produced faster. Antibodies are produced in greater concentration. |
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What is a vaccine? |
A weakened (attenuated) form of a pathogen/micro-organism that stimulates production of antibodies/plasma cells/memory cells. |
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How are memory cells important by vaccination? |
Memory cells are stored from previous infection so when there is contact with the same antigen there is a more rapid response with more antibodies that destroy the pathogen before it causes harm. |
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Why does an antibody only react with one type of antigen? |
Antibody has a binding site with a specific tertiary structure, antigen is complementary to the binding site. Antigen binds to antibody to form an antibody-antigen complex. |
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What are the features of a successful vaccination programme? |
Economically available in sufficient quantities, Few side effects, Available means of storage and transport, Means of proper administration of the vaccine, Must be possible to vaccinate vast majority of vulnerable population. |
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Why do vaccinations not eliminate disease? |
Vaccination may fail to induce immunity in individuals with defective immune systems. Individuals may develop the disease immediately after vaccination but before their immunity levels are high enough to prevent it; individuals may harbour pathogen and infect others. Pathogen may mutate frequently so its antigens will change; vaccines may suddenly become ineffective because no antigens are recognised by the immune system. May not be able to develop a vaccine for a certain pathogen (eg, common cold virus). Certain pathogens 'hide' from the body's immune system Individuals may have objections to vaccinations (eg, for religious, ethical or medical reasons). |
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How do you produce monoclonal antibodies? |
Mouse is exposed to non-self material. B-cells in mouse produce mixture of polyclonal antibodies, which are extracted from the spleen. These are mixed with cells that can rapidly divide outside the mouse's body (eg, tumour cells). This enables B-cells to divide. Detergent is added to break down cell membranes and enable fusion. Fused cells are separated and each single cell is cultured to form a clone. Any clone producing the required antibody is grown on a large scale antibodies are extracted from the growth medium. |
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Why are they called monoclonal antibodies? |
They are identical antibodies produced from a single clone of B-plasma cells. |
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Why are tests involving monoclonal antibodies specific? |
They have a specific sequence of amino acids in their primary structure so this generates a specific tertiary structure. This only binds to antigens that have a complementary shape and will not bind to any other antigen to form an antibody-antigen complex. |
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What are the functions of monoclonal antibodies? |
Separation of a chemical from a mixture, Immunoassay, Cancer treatment, Transplant surgery, Pregnancy tests. |
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Define passive immunity. |
Produced by introduction of antibodies into an individual from an outside source - the immunity is short lived - antibodies are not produced by the individuals. |
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Define active immunity. |
Antibodies produced via humoral immune response - the immunity is longer lasting. |
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Provide an example of monoclonal antibodies used to treat cancer. |
Herceptin is a MAB used to treat breast cancer; it has minima effect on other types of tissue therefore there are less side effects. |
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What are the ethical issues associated with using monoclonal antibodies? |
Production involves use of mice to produce antibodies and tumour cells - animal rights. There have been a small number if reported deaths in using MABs o treat multiple sclerosis (important to receive informed patient consent). Drug trials pose certain dangers to patients taking part, eg, in 2006, 6 volunteers testing a new MAB suffered from multiple organ failures as their immune response was over-stimulated and attached body tissue. |
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What does HIV stand for? |
Human Immunodepenency Virus |
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How does HIV replicate inside the body? |
HIV is a retrovirus so it has the ability to create DNA from RNA. Virus enters bloodstream and circulates. a protein on HIV binds to CD4, a protein receptor on T-helper cells. Capsid of HIV fuses with cell membrane - RNA and enzymes enter the T-helper cell. Reverse transcriptase enzyme from HIV converts viral RNA to DNA. Viral DNA moves into T-helper cell nucleus where it inserts into the cells DNA. Using the host cells enzymes the DNA is copied by messenger RNA. HIV particles break away from the T-helper cells with a piece of cell membrane surrounding them this forms the lipid envelope. Replication often goes into dormancy and recommences many years later, leading to AIDS. |
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How does HIV cause the symptoms of AIDS? |
Interfers with the normal function of T-helper cells. Lower numbers of T-helper cells in the blood. B-plasma cells and T-cytotoxic cells cannot be stimulated. Memory cells can also become infected or destroyed. Sufferers become susceptible to infections and cancers. many experience weight loss and diarrhea as well as infections of the lungs, intestines, brain and eyes. |
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What are the stages of HIV called? |
1 - Acute infection: during this time large amounts of the virus are being produced; many experience flu-like symptoms. 2 - Clinical latency: during this stage HIV reproduces at very low levels, although it is still active. Many people do not experience symptoms and without treatment this period lasts on average of 10 years. 3 - AIDS: as CD4 cell levels fall below 200 cells/mm^3 this is considered AIDS. Without treatment people typically live around 3 years. |
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Why are antibiotics ineffective against viral disease? |
Most antibiotics work by interfering with the formation of the bacterial cell wall. This means that there is nothing to withstand the high pressure caused by the osmotic entry of water in the cell so pathogens burst. But viruses have a cell wall so antibiotics are ineffective therefore it is important not to take antibiotics if you think you have a viral infection. |
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Describe the ELISA test. |
Enzyme linked immunosorbant assay. Antibodies are used to detect the presence of an antigen into a sample. Sensitive - detects small quantities. Can be used to detect HIV, TB and hepatitis. Useful where the quantity of an antigen needs to be measured and in drug and allergy testing. Explains monoclonal antibodies - specific Causes a colour change (catalysed by an enzyme attached to MAB). |
