Unit 1 Essay Questions

Question 1

Give an account of enzyme activation (5 marks)?

Answer 1

1) Modulators regulate the activity of the enzyme.
2) Modulators bind at allosteric sites.
3) Causes a conformation/shape change in the enzyme.
4) Alters the affinity of the active site for the substrate.
5) Positive modulators increase the enzyme affinity for the substrate.
6) Negative modulators reduce the enzyme’s affinity for the substrate.
7) Phosphorylation/addition of a phosphate or removal of a phophate/dephosphorylation can alter enzyme activity.
8) Kinase enzymes carry out phosphorylation/adds phosphate.
9) Phosphatase enzymes carry out dephosphorylation/remove a phosphate.
10) Some enzymes are activated by phosphorylation while others are inhibited.

Question 2

Give details of the structure of proteins including primary, secondary, tertiary and quaternary levels (10 marks)?

Answer 2

1) Primary structure of a protein is the sequence of amino acids in the polypeptide chain.
2) Amino acids are joined together by peptide bonds.
3) Secondary structure of a protein is stabilised by hydrogen bonds.
4) α-helix and β-sheet are two types of secondary structure.
5) α-helix is a spiral with the R groups sticking outwards.
6) β-sheet has parts of the chain running alongside each other forming a sheet.
7) The R groups sit above and below the sheet.
8) β-sheet can be anti-parallel or parallel.
9) Turns are a third type of secondary structure.
10) The polypeptide folds into a tertiary structure.
11) Folding at this level is stabilised by many different interactions between the R groups of the amino acids.
12) Any two from: hydrophobic regions, ionic bonds, hydrogen bonds, London dispersion forces, disulfide bridges.
13) A protein may include prosthetic (non-protein) parts.
14) For example, haem in haemoglobin.
15) Quaternary structure exists in proteins with two or more connected polypeptide subunits.

Question 3

Describe the action of the sodium potassium pump (10 marks)?

Answer 3

1) The sodium potassium pump transports ions against a steep concentration gradient.
2) The sodium potassium pump requires energy from hydrolysis of ATP.
3) The maintenance of ion gradients by the pump accounts for a significant part of basal metabolic rate.
4) The protein has high affinity for sodium ions inside the cell/sodium ions from inside the cells bind.
5) The protein becomes phosphorylated by ATP…
6) …which changes the conformation (of the pump)
7) The affinity for sodium ions decreases resulting in sodium being released outside of the cell.
8) Potassium ions from outside the cell bind to the sodium potassium pump.
9) Dephosphorylation occurs…
10) …which changes the conformation (award once only).
11) Potassium ions are taken into the cell.
12) The affinity returns to the start.
13) Three sodium ions are transported out of the cell and two potassium ions are transported into the cell.

Question 4

Give an account of cell signalling (10 marks)?

Answer 4

1) Some signalling molecules/hormones are proteins/peptides/hydrophilic.
2) Hydrophilic/protein/peptide signalling molecules/hormones cannot cross the membrane.
3) The receptor for hydrophilic signals is in the membrane.
4) Binding changes the conformation of the receptor.
5) Receptors cause transduction/trigger cell response.
6) Example - insulin triggers recruitment of GLUT4/glucose transporters to the cell membrane.
7) Hydrophobic signals/steroid hormones can pass through the membrane.
8) The receptor for hydrophobic signals/steroid hormones is inside the cytosol/nucleus.
9) The receptors for hydrophobic signalling molecules are transcription factors.
10) The hormone-receptor complex binds to specific DNA sequences called hormone response elements (HREs).
11) Binding at these sites influences the rate of transcription.
12) Each steroid hormone affects the gene expression of many different genes

Question 5

Describe the control of apoptosis (5 marks)?

Answer 5

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Question 6

Describe the cell cycle. (10 marks)

Answer 6

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