Intracellular signalling pathways receptor//effector mechanisms

Question 1

Three super families of cell-surface receptor

Answer 1

G-protein coupled seven transmembrane receptors
ligand gated ion channels
receptors with intrinsic enzymatic activity - tyrosine kinases

Question 2

Antagonist

Answer 2

Both the receptor but does not activate it, blocks agonist binding

Question 3

G-protein coupled receptors can respond to a variety of stimuli

Answer 3

Irons
neurotransmitters- acetylcholine
peptides- adrenaline
glycoproteins- thyroid stimulating hormone

Question 4

Describe a G-protein coupled receptor structure

Answer 4

Basic single polypeptide chain- length varies due to additions to N or C terminus
seven transmembrane spanning regions
extracellular N terminus
intracellularC

Question 5

Two regions that G-protein coupled receptors can bind ligand

Answer 5

Ligand binding site formed by two or three of the transmembrane domains
or
N terminus region

Question 6

Howard G protein coupled receptors cause a change in CELLULAR activity

Answer 6

G-protein coupled receptor must interact with the guanine nucleotide binding protein

Question 7

Describe the structure of the G-protein

Answer 7

Made up of three subunits Heterotrimerric
Alpha
beta
gamma

Question 8

An inactive G protein binds

Answer 8

GDP

Question 9

An active G-protein

Answer 9

Alpha subunit binds GTP

beta and gamma subunits dissociate

Question 10

How signal terminated

Answer 10

Alpha subunit has a GTP is activity hydrolyse is back to GDP then the beta gamma subunit will be associated with the alpha to reform the hetero complex

Question 11

What governs receptor G-protein selectIVITY

Answer 11

Activated G-protein coupled receptors interact with a specific type of G-protein, the G alpha subunit is the primary determinant

The G alpha subunit and the G beta and gamma interact with specific effector proteins

Bring around a specific sailor response

Question 12

Explain QISS QIQ

Answer 12

Q I S S(sym) Q I Q (parasymaotheitc) type od G alpha subunit
a1a2b1b2     M1M2M3 (receptor)

Q- stimulates phospholipase C
I inhibits adenylyl cyclase
S stimulates adenylyl cyclase

Question 13

Cholera toxin

Answer 13

Gs

Prevents GTPase activity, therefore constantly stimulated activates lots of adenylyl cyclase

Question 14

Pertussis toxin (causes whooping cough)

Answer 14

Gi
because it is an inhibitory G protein normally would stop adenylyl cyclase so would change from GTP to GDP

However pertussis toxin interferes with Gi therefore can no longer lose the GTP so constantly on