extended response unit 1

Question 1

A Discuss the role of amino acid R-groups in:
(i) the determination of tertiary structure of proteins;

Answer 1

• tertiary structure
• shape determined by order of amino acids, r group interaction
• r-groups
• types of interactions

Question 2

Discuss cell membranes under the following headings:
(i) the phospholipid bilayer as a selective barrier;

Answer 2

1 Membrane has hydrophilic and hydrophobic regions.
2. Polar/charged/hydrophilic substances can’t cross/pass
through (membrane).
3. Oxygen/carbon dioxide/water pass through.
4. Protein channels/pumps/ transporters needed for
hydrophilic/polar/charged substances to cross.

Question 3

Discuss cell membranes under the following headings:
(ii) types of transport proteins and their functions

Answer 3

• channels are transmembrane
• control ion concentrations
• different cell types have different channel proteins
• diffusion
• change conformation
• active transport requires ATP
• ligand channels
• voltage channels

Question 4

Discuss signalling between cells under the following headings.
(i) Hydrophilic signalling molecules and signal transduction

Answer 4

1. neurotransmitters
2. peptide/protein hormones
3. receptor is specific
4. receptors are transmembrane
   proteins
5. binding (to receptor) at cell surface/
   plasma membrane
6. binding to receptor causes
   conformational change
7. bringing about a response/change
   inside the cell

Question 5

Describe the generation and transmission of a nerve impulse in a neuron.

Answer 5

• resting membrane potential
• vesicles containing neurotransmitter fuse with membrane
• bind to specific receptors
• receptors are ligand gated channels
• binding of neurotransmitter opens channels
• sodium ions enter
• depolarisation of plasma membrane
• sufficient ion movement
• opens voltage gated sodium
• further depolarisation