2017 Bio H2 MCQ Explanations

1. N17Q1 A We are told that the cell is “metabolically active”. 1 is mitochondrion and the chemical inhibits oxidative oxidation in the organelle and thus it cannot carry out its role for ATP production. 2 is heterochromatin and 3 is RER. E nergy in the form of ATP is needed by chromatin remodelling complexes to induce changes in conformation at the level of the nucleosome in 2 to form euchromatin, so that there is more transcription and subsequently more translation ( protein synthesis). RER ribosomes would have their functions impaired due to no protein synthesis. 2. N17Q2 A T4 phage has all 3 characteristics. For phage lambda, it would be 2 and 3 only. 3. N17Q3 A Molecule A, the 1,4 glycosidic bond formed between 2 alpha-glucose are beside each other. The 1,6 glycosidic bond is formed between the second and rightmost molecule. The rightmost molecule is a beta glucose as shown by the OH on C1 being above the ring. Molecule B has both 1,4 and 1,6 glycosidic bonds formed from 3 alpha glucose. Molecule C has all 3 beta glucose. Molecule D has 2 alpha glucose and 1 beta glucose (extreme right), but has both 4,4 and 1,6 glycosidic bonds (no 1,4) 4. N17Q4 C Carbohydrate chains on the cell surface membrane are responsible for cell -cell recognition and cell to cell adhesion which allow for assembling . 2,5,6 are glycoproteins and 4 is a glycolipid. 5. N17Q5 A Z must be quaternary as it has 2 polypeptides coded by 2 genes , X and Y are coded by only 1 gene each, so tertiary structure. Y must be globular as it a great number of different aa than X , hence not many repetitive amino acids . X is fibrous as there is a high percentage of commonest amino acids, suggesting repetitive amino acids. (Remember collagen has repetitive amino acids). 6. N17Q6 B GPCR is embedded on membrane hence has hydrophobic R groups associated with the hydrophobic core of the phospholipid bilayer. GPCR is not quaternary (Option D is wrong) Option A is for fibrous protein. 7. N17Q7 C Options A, B and D apply to all enzymes whether lock-and-key hypothesis is used or induced fit hypothesis is used. Only option C applies to induced fit, where the active site of the enzyme changes conformation to fit the substrate better once the substrate approaches the active site, so the ES complex is formed. In lock-and-key hypothesis, the active site and substrate are an exact fit and there is no further conformational change after substrate binds. 8. N17Q8 A Resistant insects do not die from insecticides sprayed o n them, because they have enzymes that metabolise (meaning “break down”) the insecticides, and so rendering the insecticides ineffective. Synergists are non-competitive inhibitors that bind to one of the enzymes in the insect’s body that metabolise (break down) the insecticides and inactivates it. Evidence 1: Resistant insects have high concentration of this enzyme but susceptible insects have low concentrations of this enzy