Cell Signalling 1

Question 1

What are the 3 membranes which carbohydrates are located on?

Answer 1

• Plasma
• Nuclear
• Mitochondrial

Question 2

What is the choline R group when attached to a phospholipid?

Answer 2

CH2, CH2, N+ (CH3)3

Question 3

What is the serine R group when attached to a phospholipid?

Answer 3

CH2, C (H)(COO-)(NH3+)

Question 4

Why must we ingest two fatty acids?

Answer 4

They cannot be made endogenously and they give rise to arachidonic acid which is involved in cell signalling.

Question 5

What are 6 effects that we need from signalling?

Answer 5

• Growth
• Differentiate
• Divide
• Secrete and release
• Die
• Store/ mobilise energy

Question 6

What are the 5 steps to communicating via extracellular signalling?

Answer 6

1. Synthesis and release of the signalling molecule by the signalling cell
2. Transport of the signal to the target cell
3. Detection of the incoming signal by a specific binding protein (receptor) at the target cell
4. Binding of the signal to the receptor generates a biological response within the target cell
5. Removal of signal - termination

Question 7

What are the 4 types of signal?

Answer 7

Hormones and growth factors
Metabolic Regulators
Neurotransmitters
Inflammatory Mediators

Question 8

What are the major types of signalling based on distance?

Answer 8

1. Endocrine signalling (secretion of hormones into the bloodstream)
2. Paracrine signalling (signalling to adjacent cells
3. Autocrine signalling (signalling back onto the same cell)

Question 9

What are the approx distances for each type of signalling?

Answer 9

Autocrine - few metres
Paracrine - few micrometres
Autocrine - same cell

Question 10

As most signalling molecules are membrane impermeable, what must they bind to?

Answer 10

Cell surface receptors in the form of integral membrane proteins

Question 11

What are the 3 major classes of membrane receptors?

Answer 11

Ionotrophic (ligand gated ion channels that allow ions to bind in order to open the channel.
Metabotrophic (7 transmembrane spanning G-protein couples)
Catalytic (tyrosine kinases linked e.g. insulin, nerve growth factor receptors)

Question 12

Give 2 examples of effector enzymes and the 2nd messenger molecules they activate

Answer 12

Adenylyl cyclase - adenosine cyclic monophosphate (cAMP)

Phospholipase C - DAG

Question 13

What is a G - protein?

Answer 13

A molecular switch which carries information to effector enzymes. They are active when bound to GTP and inactive when bound to GDP.

Question 14

What subunit of G - proteins binds to GTP and becomes activated?

Answer 14

Alpha subunit

Question 15

What happens with GTP binds to the G- protein?

Answer 15

It dissociates, releasing the free active alpha sub unit. Reassociates when GTP is hydrolysed to GDP byt a GTPase activity.

Question 16

What are the 7 steps to G protein coupled receptor signalling to effector enzymes?

Answer 16

1. Hormones binds to receptor
2. G - protein (GDP bound) associates with receptor
3. GTP/GDP exchange on G - protein (GTP bound)
4. G - protein dissociates into into GTP bound alpha and a beta-gamma subunit
5. A subunit (with GTP bound) activates effector enzyme
6. Effector enzyme produces 2nd messenger
7. GTP hydrolysed to GDP, G-protein complex reassociates and signalling ends

Question 17

What is the purpose of the GPCR signalling producing a GTP bound alpha subunit? What causes this reaction to stop?

Answer 17

Causes cAMP from ATP to be produced leading to a cascade reaction.
Stopped by when GDP binds to alpha subunit and it can no longer fir the binding site.

Question 18

What happens with cAMP binds to another PKA?

Answer 18

A conformational change so cAMP breaks apart and exposes the catalytic part.
This can then phosphorylate proteins.

Question 19

How many units does PKA have? After breakdown, what subunit can take a phosphate group and phosphorylate serine?

Answer 19

4, C subunit

Question 20

What is the process of phosphodiesterase?

Answer 20

The degradation of cAMP by PKA by turning it to 5AMP. cAMP can then not bind to PKA so the signal ends.

Question 21

What stimulates PKA? What can PKA then do once stimulated?

Answer 21

cAMP - PKA can then phosphorylate some proteins or inhibit glycogen synthesis.

Question 22

What effector can both increase and decrease cAMP concentration?

Answer 22

Adenylyl cyclase