Biology AQA A-Level processes/long mark questions

Properties of water

1. A metabolite in condensation/hydrolysis/photosynthesis/respiration;

2. A solvent so metabolic reactions can occur/so allowing transport of substances;

3. High heat capacity so buffers changes in temperature;

4. Large latent heat of vaporisation so provides an evaporative cooling effect;

5. Cohesion (between water molecules) so supports columns of water (in plants);

6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;

Protein structure

1. primary structure amino acids joined by peptide bonds in condensation reaction;

2. Secondary structure is formed by hydrogen bonding (alpha helix or beta pleated sheet)

3. Tertiary structure formed by interactions between R groups, (disulphide bridges, ionic bonds, hydrogen bonds);

4.. Quaternary structure formed by bonds between 2 or more polypeptides;

Enzyme action (induced fit model)

1. Substrate binds to the active site forming enzyme-substrate complex;

2. Active site changes shape so it is complementary to substrate

3. Reduces activation energy;

Competitive inhibitor

1. Has a similar shape to substrate and is complementary to enzyme active site

2. Competes with substrate by binding at active site of enzyme;

3. Fewer enzyme-substrate complexes;

Non-Competitive Inhibitor

1. Binds to the enzyme at a site other than the active site;

2. Alters tertiary structure of enzyme, changing shape of the active site;

3. Active site and substrate no longer complementary;

4. Fewer enzyme-substrate complexes;

Protein Trafficking

1. DNA in nucleus codes for enzyme/protein production;

2. Ribosomes produce enzyme/protein by translation;

3. Rough endoplasmic reticulum transports enzyme/protein;

4. Mitochondria produce ATP (for peptide bonds/vesicle movement);

5. Golgi apparatus modifies enzyme/protein and releases vesicles;

6. Vesicles move to cell membrane and fuse with cell membrane;

TEM vs Optical Microscopes

1. TEM use electrons and optical use light;

2. TEM allows a greater resolution;

3. (So with TEM) smaller organelles/greater detail can be observed;

4. TEM view only dead/dehydrated specimens and optical (can) view live specimens;

5. TEM does not show colour and optical (can);

6. TEM requires thinner specimens;

7. TEM requires a more complex/time consuming preparation;

8. TEM focuses using magnets and optical uses (glass) lenses;

Cell Fractionation and Ultracentrifugation

1. Homogenise tissue to break open cells

2. Filter to remove unbroken cells/debris;

3. Cold solution to prevent enzyme activity to prevent damage to organelles;

4. Solution with equivalent water potential to prevent osmosis bursting/shrinking organelles;

5. Buffered solution to stop enzymes/protein denaturing;

6. Centrifuge at lower speed so nuclei in pellet;

7. Centrifuge supernatant at increasingly higher speeds to separate organelles by density