BI203 Lecture 21: Cell Signaling - Slides 31-49 (G-Protein Coupled Receptors)

Question 1

___ ___ receptors are the largest family of cell surface receptors.

Signals are transmitted via guanine nucleotide-binding proteins (G proteins).

The receptors have seven membrane-spanning α helices.

Answer 1

G protein-coupled receptors

Question 2

Signaling from G protein-coupled receptors begins with the activation of ___ ___.

Answer 2

G proteins

Question 3

G proteins were discovered during studies of ___, a secondary messenger that mediates responses to many hormones.

A G protein is an intermediate in adenylyl cyclase activation, which synthesizes ___.

Answer 3

cAMP (cyclic AMP)

Question 4

Binding of a ligand induces a conformational change that allows the ___ domain to activate a G protein on the inner face of the plasma membrane.

The activated G protein then dissociates from the receptor and carries the signal to an intracellular target.

Answer 4

cytosolic domain

Question 5

G proteins have three subunits designated ___, ___, and ___.

Answer 5

α, β, γ

Question 6

G proteins have three subunits designated α, β, and γ.

They are called ___ G proteins to distinguish them from other small GTP-binding proteins, such as the Ras, Ran and Rab proteins.

Answer 6

heterotrimeric G proteins

Question 7

In the inactive state, α is bound to ___ in a complex with β and γ.

Answer 7

GDP

Question 8

Hormone binding to the receptor causes exchange of GTP for GDP. The α and βγ complex then ___ from the receptor and interact with their targets, such as adenylyl cyclase.

Answer 8

dissociate

Question 9

cAMP is formed from ATP by adenylyl cyclase and degraded to AMP by ___ ___.

Answer 9

cAMP phosphodiesterase

Question 10

Effects of cAMP are mediated by a cAMP-dependent protein kinase, or ___ ___ ___.

Inactive form has two regulatory and two catalytic subunits. cAMP binds to the regulatory subunits, which dissociate.

The free catalytic subunits can then phosphorylate serine on target proteins.

Answer 10

protein kinase A (PKA)

Question 11

In glycogen metabolism, protein kinase A phosphorylates two enzymes:

___ ___ is activated, which in turn activates ___ ___, which catalyzes glycogen breakdown.

Answer 11

Phosphorylase kinase, glycogen phosphorylase

Question 12

After an increase in cAMP and the activation of PKA, PKA can enter the nucleus and phosphorylate the transcription factor ____.

Answer 12

CREB (CRE-binding protein)

Question 13

CRE = ___ ___ ___.

Answer 13

cAMP response element

Question 14

___ is another important secondary messenger formed from GTP by guanylyl Cyclades and degraded to GMP by a phosphodiesterase.

Answer 14

cGMP (cyclic GMP)

Question 15

The photoreceptor in retinal rod cells is a G protein-coupled receptor called ___.

Answer 15

rhodopsin

Question 16

Rhodopsin is activated by light, which then activates the G protein ___.

Answer 16

transducin

Question 17

Transducin stimulates ___ ___, leading to decreased levels of cGMP.
cGMP levels are translated to nerve impulses by a direct effect of cGMP on ion channels.

Answer 17

cGMP phosphodiesterase

Question 18

Heart muscle cells have acetylcholine receptors that are G protein-coupled.

The α subunit of this G protein (Gi) inhibits ___ ___.

The Gi βγ subunits open ___ channels in the plasma membrane, which slows heart muscle contraction.

Answer 18

adenylyl cyclase, K+