L25

Question 1

Why would a cell send a signal to another cell? (4)

Answer 1

Survival, growth & division, differentiation, death

Question 2

What are the major components of a signalling pathway?

Answer 2

1) Extracellular signal molecule
2) Receptor protein
3) Intracellular signalling proteins
4) Effector proteins

Question 3

What provides signalling pathways with their specificity? What can amplify a signal?

Answer 3

Specific binding sites. Enzymes activate other enzymes to amplify a signal.

Question 4

Are signals usually transient or long-lived? How is this achieved?

Answer 4

Transient for extracellular signalling

Question 5

What does it mean that something is a molecular switch? What is on and what is off in each of the generalised molecular switches?

Answer 5

Allowing molecules to switch on (phosphorylation, GTP binding) and switch off (protein phosphatase, GTP hydrolysis)

Question 6

What is the basic structure of the components of the G protein-coupled receptor pathway?

Answer 6

7 transmembrane domain, alpha and gamma subunits have lipid molecules that insert into the membrane. The alpha subunit has a GDP binding site and has GTPase activity.

Question 7

How does a G protein-coupled receptor transmit the activation signal? How does it act as a molecular switch?

Answer 7

GTP switches it on and GTPase activity of alpha subunit hydrolyses the GTP

Question 8

What does the βadrenergic receptor respond to, and what does it pass its signal to?

Answer 8

Epinephrine and passes its signal adenylyl cyclase to increase cAMP

Question 9

What is a receptor tyrosine kinase? Give one example.

Answer 9

Enzyme-coupled ell surface receptor.

Insulin receptor

Question 10

What is their immediate phosphorylation target?

Answer 10

The tyrosine kinase domain

Question 11

What common intracellular signalling pathways are downstream of the insulin receptor?

Answer 11

1) Insulin receptor binds insulin and undergoes autophosphorylation on its carboxyl-terminal Tyr residues
2) Insulin receptor phosphorylates IRS-1 on its Tyr residues
3) SH2 domain of Grb2 binds to P-Tyr of IRS-1. Sos binds to Grb2, then to Ras, causing GDP release and GTP binding to Ras.
4) Activated Ras binds & activates Raf-1
5) Raf-1 phosphorylates MEK on 2 Ser resiudes, activating it. MEK phosphorylates ERK on a Thr and a Tyr residue, activating it
6) ERK moves into the nucleus and phosphorylates nuclear transcription factors such as Elk1, activating them.
7) Phosphorylated Elk1 joins SRF to stimulate the transcription and translation of a set of genes needed for cell division