Receptors

Question 1

In what two ways can intercellular signalling occur?

Answer 1

Secretion of signalling molecules which act in receptors and also signalling by plasma-membrane molecules when cells are close together.

Question 2

In paracrine signalling, what is the signalling molecule?

Answer 2

A local mediator.

Question 3

What type of signalling is it if the signalling molecule is a hormone?

Answer 3

Endocrine

Question 4

How can we tell if a signalling molecule will act on an extra or intracellular receptor?

Answer 4

Hydrophilic signalling molecules cannot cross the plasma membrane and so they will act on cell-surface receptors. Small Hydrophobic signalling molecules can so they cross the membrane and act on intracellular receptors.

Question 5

Define a receptor.

Answer 5

It is a molecule which specifically recognises another molecule or family of molecules, and this leads to regulation of a cellular process.

Question 6

What is a ligand?

Answer 6

This is a molecule that binds specifically to a receptor site.

Question 7

What is the difference between an agonist and an antagonist?

Answer 7

An agonist binds to a receptor leading to activation, an antagonist binds to a receptor but there is no activation of the receptor.

Question 8

What is KD?

Answer 8

This is the concentration of ligand at which half of the receptor sites are full.

Question 9

What can be said about receptors when they are at rest (nothing is bound to them)?

Answer 9

At rest, receptors are functionally silent.

Question 10

What else is needed besides ligand binding to cause a cellular response?

Answer 10

Usually a substrate is also needed for example Na to move through sodium channels.

Question 11

Name the four different types of signal transduction in cells.

Answer 11

Integral ion channels, integral enzyme activity, coupled to effectors via transducing proteins, intracellular response.

Question 12

What method of signal transduction do nicotinic acetyl choline receptors employ?

Answer 12

These have integral ion channels. On binding of the ligand, the channel opens and then there is Na+ entry.

Question 13

When membrane receptors are linked to integral enzyme activity, what occurs?

Answer 13

On binding of the ligand there is a conformational change which reveals an active site on the membrane which was not present before.

Question 14

What molecule are growth factor receptors linked to?

Answer 14

Tyrosine kinase.

Question 15

How does a transducing protein increase cellular response?

Answer 15

Transducing proteins have many tyrosine residues which become phosphorylated. These can then carry the signal to the cell, phosphorylating multiple enzymes and so there is a faster response.

Question 16

How do insulin receptors work?

Answer 16

Insulin receptors have both a and b subunits and when insulin binds to the receptor, there is a conformational change and the tyrosine kinase domain becomes activated.

Question 17

What are the most common transducing protein signalling receptors?

Answer 17

GPCRs. This includes adrenoceptors and muscarinic acetyl choline receptors.

Question 18

How do GPCRs have both activatory inhibitory effects on cells?

Answer 18

Different G proteins will activate different molecules which will have different effects on the cell, having opposing effects on the same enzyme and so causing a different response.

Question 19

How do intracellular receptors normally work?

Answer 19

Typically the DNA binding site is blocked at rest, and when the ligand binds to this site it leads to conformational site so that the DNA binding site becomes exposed.

Question 20

How is there signal amplification for intracellular receptors?

Answer 20

When a ligand binds to a receptor, this leads to Multiple proteins being activated which then activate multiple other molecules and so over time a signal cascade occurs.