Week 5 - Cell Communication and Signalling

Question 1

Effects of phosphorylation

Answer 1

• activate or inactivate an enzyme
• increase or decrease protein-protein
  interactions
• activate intracellular transport of protein
• activate protein degradation

Question 2

Outcome of signal transduction

Answer 2

• change in gene expression
• alteration of activity of metabolic
  enzymes

Question 3

GPCR and blood glucose

Answer 3

signal goes into the receptor
prompts the production of cAMP by adenylyl cyclase
activation of protein kinase a
protein kinase a leads to the activation of other mechanisms
a) activates
phospghorylase kinase -> activates
glycogen phosphorylase -> removes
glucose from glycogen
b) deactivation of glycogen synthease
c) activation of CREB gene to affect gene expression of enzymes in glucose mechanism

Question 4

G Protein Activation

Answer 4

1. ligand binds to the receptor
2. GDP replaced by GTP on alpha subunit
3. GTP bound G-a has lower affinity for Gby -> Ga binds with effector
4. Secondary messenger (cAMP) generated
5. GTP-Ga to GDP-Ga hydrolysis occurs
6. GDP-Ga detaches from effector and reassociates with Gby

Question 5

RTK

Answer 5

Receptor protein-tyrosine kinase
1. Extracellular messenger binding to RTKs leads to receptor dimerization
2. Dimerization leads to autophosphorylation and activation of kinase
3. RTK links with adaptor proteins (mediate phosphorylation-dependent
protein-protein interactions)

Question 6

SH2 and SH3 domains are normally found in RTK signalling complexes, which are…

Answer 6

SH2 domains: phosphorylated tyrosine
SH3 domains: proline rich

(e.g. in virus HBx from hepatitis B has a proline rich region, which binds to SH3, disrupts cell adhesion)

Question 7

RTK Activated RAS signalling

Answer 7

Inactive G Protein
Activated by GEF (guanine exchange factor)
GEF: GDP -> GTP
Activated G Protein attaches with inactive target protein
GAP (GTPase activation protein) acts as a clock for the signalling period
Once back to GDP, GDI (guanine nucleotide dissociation inhibitor) locks G protein in inactive state

Question 8

RTK Activated Ras-MAP signalling

Answer 8

Signal attaches to from outside the cell
Attaches to Grb2 (adaptor protein)
Attachment of SOS (GEF)
Activation of RAS
Activation of Raf (membrane bound MAPKKK)
Activation of MEK, ERK (MAPKK, MAPK)
Activation of transcrption factors, leading to higher DNA binding activity, increase in target gene expression

Inhibitor produced: MKP-1 dephosphorylates ERK, inhibition can also be through recycling of receptor

Question 9

GPCR activation termination

Answer 9

GPCR phosphorylation by GPCR-kinase
Attaches to arrestin, leading to endocytosis