Biochemistry

Question 1

At which point in eukaryotic cell division can the cells go into a quiescent state?

Answer 1

G0

Question 2

At which point in eukaryotic cell division is DNA checked?

Answer 2

Before and during S phase

Question 3

Action of Gq protein coupled receptor?

Answer 3

Activates phospholipase C which cleaves phosphatidyl bisphosphate (PIP2) into inositol triphosphate (IP3) and diacylglycerol.

IP3 binds to ER and releases Ca2+

Rise in Ca2+ allows diacylglycerol to activate protein kinase C which phosphorylates proteins’ serine/threonine residues
Diacylglycerol can also be cleaved to give arachidonic acid (precursor of eicosanoid synthesis)

Question 4

Action of Gs protein coupled receptor?

Answer 4

Gs stimulates adenylate cyclase which transforms ATP into cAMP (cyclic adenosine monophosphate) by removing two phosphate molecules

cAMP binds to protein kinase A, separating regulatory and catalytic subunits
Catalytic subunit phosphorylates proteins

Question 5

Action of Gi protein coupled receptor?

Answer 5

Gi inhibits adenylate cyclase which causes negative feedback to protein Gs, inactivating cells

Question 6

General action of G protein coupled receptors?

Answer 6

G protein alpha subunit is bound to guanosine diphosphate (GDP), ligand causes alpha subunit to switch to GTP which then causes it to dissociate from beta and gamma subunits, exposing binding site