G-proteins

Question 1

Examples of Transmembrane Messengers

Answer 1

• ions
• lipid-soluble molecules
• actively transported molecules

Question 2

Examples of Membrane-Bound Messengers

Answer 2

• receptors
• βγ G-proteins
• PLC

Question 3

Examples of Diffusible Intracellular Messengers

Answer 3

• Ca2+
• ATP, GTP
• α G-proteins

Question 4

Examples of Genomic/Proteomic Messengers

Answer 4

• transcriptional
• translational
• post translational

Question 5

Ionotropic Receptor Coupling Mechasim

Answer 5

Ions move through the integral ion channels

Question 6

Metabotropic Receptor Coupling Mechanism

Answer 6

Acts through second messenger systems

Question 7

Membrane Kinases

Answer 7

Enzyme-linked receptors that stimulates intrinsic enzymatic activity when activated

Question 8

Intracellular Receptors

Answer 8

Receptors found in the cytosine the cell and known to affect transcription

Question 9

Humans have over ______ types of G-protein coupled receptors.

Answer 9

1,000

Question 10

What does the “o” in “oGPCR” stand for?

Answer 10

“Orphan”; the corresponding ligands for these receptors are not yet known

Question 11

How many transmembrane subunits do GPCRs have?

Answer 11

7

Question 12

What are the 3 subunits of a G-protein?

Answer 12

Alpha, beta, and gamma subunits

Question 13

α G-proteins bind guanine nucleotides such as _____ and ______.

Answer 13

GTP & GDP

Question 14

α G-proteins have a higher affinity for βγ when it is bound to _____ and a lower affinity when bound to _____.

Answer 14

GDP; GTP

Question 15

Are α G-proteins diffusible monomers?

Answer 15

Yes; they are free to move about the cytosol and not membrane bound

Question 16

Gamma proteins are bound to ________ proteins and have a lipophilic tail

Answer 16

Beta

Question 17

Guanine Exchange Factors (GEFs)

Answer 17

Speed up the rate at which GDP is hydrolyzed to GTP on the α subunit of the G-protein

Question 18

GTP-ase Activating Proteins (GAPs)

Answer 18

Bind to α subunits and stimulate their intrinsic GTP-ase activity

Question 19

GTP-ase Inhibiting Proteins (GIPs)

Answer 19

Slow down the rate of GTP-ase activity

Question 20

What are the initial conditions for the G-protein life cycle?

Answer 20

1) free ligand
2) unbound receptor
3) inactive G-protein nearby not linked to receptor
4) free GTP in vicinity

Question 21

What α subunits upregulate adenylate cyclase (AC)?

Answer 21

αs subunits (Gs family)

Question 22

What α subunits downregulate adenylate cyclase (AC)?

Answer 22

αi and αo subunits (Gi family)

Question 23

What α subunits upregulate PLC?

Answer 23

αo subunits (Gi family) and αq subunits (Gq family)

Question 24

What α subunits downregulate PLC?

Answer 24

None known

Question 25

What is the non-hydrolyzable form of GTP? What effect does it have on the alpha subunit?

Answer 25

GTPγs; the alpha subunit in this form will remain constantly active

Question 26

The cholera toxin binds to _______ in the amino acid sequence of the _____ family alpha subunit

Answer 26

αs; arg

Question 27

The pertussis (whooping cough) toxin binds to _____ in the amino acid sequence of the ______ family alpha subunits

Answer 27

αi and αo; cys

Question 28

What effect do the cholera and pertussis toxins have on α subunits?

Answer 28

They cause persistent activation

Question 29

True or False: messenger-effector systems are always stimulatory

Answer 29

False; messenger-effector systems can be inhibitory as well as stimulatory

Question 30

Transmembrane proteins that link receptors to effectors

Answer 30

G-proteins