Intracellular Signalling - Signal Transduction

Question 1

What is purpose of signal transduction?

Answer 1

Converts extracellular signal (1st messenger) into a cellular response

Question 2

Describe signal transduction of adrenaline and cell

Answer 2

1. Cell –> liver or skeletal muscle
2. 1st messenger –> adrenaline
3. Receptor –> beta-adrenergic receptor
4. G-protein
5. Effector enzyme –> adenyl cyclase
6. 2nd messenger –> cyclic AMP
7. Protein kinase –> protein kinase A
8. Cell response –> breakdown of energy reserves (glycogen) to form glucose

Question 3

How does adrenaline stimulate glycogen breakdown in liver/skeletal cells to produce glucose?

Answer 3

1. 1st messenger (adrenaline) binds to receptor on cell surface (beta-adrenergic receptor)
2. Activation of G-protein which stimulates an effector enzyme (adenyl cyclase)
3. Effector enzyme catalyses production of 2nd messenger molecules (cyclic AMP)
4. This stimulates a protein kinase (protein kinase A) to phosphorylate specific target proteins
5. Alters their function and causes response

Question 4

How can a single 1st messenger molecule lead to larger cellular response?

Answer 4

Amplification –> can induce many downstream signalling molecules

Question 5

What are the main points of amplification?

Answer 5

1. G-protein activation
2. Effector enzyme
3. Protein kinase

Question 6

How are G-protein involved in amplification?

Answer 6

Activated by receptor (as long as the receptor remains in activated state)

One can activate many effector enzymes

Question 7

How are effector enzymes involved in amplification?

Answer 7

Will catalyse reactions without being used up

One can catalyse production of many 2nd messengers

Question 8

How are protein kinases involved in amplification?

Answer 8

Protein kinase is enzyme –> one can catalyse phosphorylation of many protein substrates

Question 9

How is signal transduction specific?

Answer 9

1st messengers can elicit different effects on different cells due to binding to different receptors and activating different signalling pathways

Question 10

Where does adrenaline stimulate fatty acid production?

Answer 10

Adipose tissue

Question 11

Where does adrenaline increase heart rate and how?

Answer 11

Cardiomyocytes by stimulating contraction of heart muscle cells

Also increases blood pressure by causing relaxation of vascular smooth muscle cells

Question 12

Where does adrenaline stimulate breakdown of glycogen?

Answer 12

In liver and muscle

Question 13

What is ‘cross talk’?

Answer 13

Interaction between different signalling pathways

The cellular response to a particular stimulus depends on many variables and is not always the same for different cell types.