Week 6 - Receptors, Basic Endocrinology and Membrane Turnover

Question 1

Define the term “receptor”.

Answer 1

A receptor is a molecule that recognises specifically a second molecule (ligand) or a family of molecules, and which in response to ligand binding brings about regulation of a cellular process.

Question 2

Define the term “ligand”.

Answer 2

A ligand is any molecule that binds specifically to a receptor site.

Question 3

Name some processes in cellular physiology that receptors play a role in.

Answer 3

1. Signalling by hormones/local chemical mediators
2. Neurotransmission
3. Control of gene expression
4. Sorting of intracellular proteins
5. Cellular delivery
6. Release of intracellular calcium stores
7. Cell adhesion
8. Modulation of the immune response

Question 4

How are receptors classified?

Answer 4

According to the specific physiological signalling molecule (agonist) recognised

Sub Classification: Affinity (tightness of binding) of a number of antagonists

Question 5

Name the two main types of acetylcholine receptors and state their respective agonists.

Answer 5

1. Nicotinic: Nicotine

2. Muscarinic: Muscarine

Question 6

Outline the three main muscarinic receptor subtypes and state their respective antagonists.

Answer 6

1. M1: Pirenzipine
2. M2: Gallamine
3. Hexahydrosiladiphenol

The most potent blocker of M1 is pirenzipine. However, it is blocked by all three in the table.

Question 7

Distinguish between a receptor and an acceptor.

Answer 7

Receptors:

1. Silent at rest
2. Agonist binding produces a biological response

Acceptor:

1. Operates in the absence of a ligand
2. Ligand binding alone produces no response

Question 8

Name modulators of the sodium channel.

Answer 8

1. Local anaesthetic agents

2. Neurotoxins

Question 9

Briefly outline the main mechanisms of membrane internalisation.

Answer 9

1. Phagocytosis: Internalisation of particulate matter
2. Pinocytosis: Invagination of plasma membrane to form a vesicle, Permits uptake of extracellular solutes
3. Endocytosis: Selective internalisation of molecules into the cell by binding to specific cell surface receptors

Question 10

Name the main subdivisions of signalling molecules.

Answer 10

1. Local chemical mediators
2. Hormones
3. Neurotransmitters