intracellular signalling

Question 1

What are some types of intracellular signals?

Answer 1

• ions
• proteins
• dissolved gases
• second messengers

Question 2

What are the two types of proteins used in signal transduction and where are they found?

Answer 2

• hydrophobic proteins (membrane-associated)
• hydrophilic proteins (cytosol)

Question 3

What are the 3 ways signalling molecules are controlled?

Answer 3

• by post translational modification
• by regulating whether a G protein has bound (GDP or GTP)
• by provision of activators

Question 4

What is kinase and what does it do?

Answer 4

• enzyme
• phosphorylates proteins

Question 5

What is phosphatase and what does it do?

Answer 5

• enzyme
• dephosphorylates proteins

Question 6

What are the 2 enzymes involved in protein phosphorylation?

Answer 6

• kinase (phosphorylates)
• phosphatase (dephosphorylates)

Question 7

What are the two types of kinases?

Answer 7

• serine/threonine kinases
• tyrosine kinases (non receptor and receptor)

Question 8

What are GEFs and what do they do?

Answer 8

• guanine exchange factors
• promote exchange of GDP for GTP

Question 9

What is Ras? Why is it significant?

Answer 9

• a small GTPase
• Ras mutations found in a large proportion of adenocarcinomas

Question 10

What are voltage gated Na+ channels composed of?

Answer 10

• 4 alpha subunits
• 4 beta subunits

Question 11

How do voltage gated Na+ channels stop other ions from getting through?

Answer 11

• too small for K+ ions to cross
• contains negatively charged amino acids to stop Cl- ions passing

Question 12

What do the alpha subunits in voltage gated Na+ channels do?

Answer 12

• opens in response to a change in voltage
• contains 4 homologous domains that form the pore

Question 13

What do the beta subunits in voltage gated Na+ channels do?

Answer 13

traffic the channel and regulate its kinetic properties

Question 14

How do the alpha subunits detect voltage?

Answer 14

• 4 homologous domains have 6 transmembrane regions
• region 4 has AA with positive R-groups which sense the voltage

Question 15

How does the nicotinic acetylcholine receptor work?

Answer 15

• 2 acetylcholine molecules bind the alpha subunits
• causes movement of the M2 helices (opens channel)

Question 16

Describe the structure of the nicotinic acetylcholine receptor

Answer 16

• 5 subunits (2 alpha, beta, gramma, delta)
• transmembrane region M2 of each subunit forms channel

Question 17

How are the effects of Ca2+ mediated?

Answer 17

• kinases (e.g CAM kinase)
• phosphatases (e.g Calcineurin)

Question 18

What types of channels are Ca2+ channels?

Answer 18

ligand gated or voltage gated

Question 19

What is the structure of a G-protein

Answer 19

alpha, beta, gamma

Question 20

How does G-protein coupled receptor activation work?

Answer 20

• ligand binds to receptor, and affinity for G-protein increases (may already be coupled)
• receptor activation changes conformation of internal portion of receptor, releasing GDP

Question 21

How does the GPCR initiation of signalling work

Answer 21

1. GDP attached to alpha subunit is replaced by GTP
2. alpha subunit and beta-gamma complex dissociate (can each initiate further signalling)
3. GTP then hydrolysed to GDP and beta-gamma recombine with alpha subunit