G Protein

Question 1

What are the two major pieces of evidence obtained in the discovery of G protein in signaling pathways?

Answer 1

GTP absolute required for glucagon action on the liver

Receptor activation leads to change of GTP in place of GDP on G protein

Question 2

Fill in the blanks

A G protein is a ___________, all units are different

__ –> has a fatty acid chain attached to cell membranes, regulate cell function and structure, like stimulatory (Gs and Gq) and inhibitory (Gi)

__ –> has a fatty acid chain attached to cell membranes, connect with another subunit

Both above subunits are cytoplasmic proteins, after post translation, an enzyme inserts a fatty acid chain into the protein, eventually increase in the plasma membrane and increase conc. The fatty acid chain tethering increases the probability of the encounter to GPCRs and activation to the effector, increase the efficiency of the signaling pathways.

___

Answer 2

heterotrimer

alpha

gamma

beta

Question 3

What are the major most widely expressed alpha subunits?

Which one stimulate the

adenylate cyclases

phospholipase Cbeta?

Which one inhibitory of the adenylate cyclases?

Answer 3

Gs, Gq, Gi

Gs stimulates the adenylate cyclases

Gq stimulate the phospholipase Cbeta

Gi inhibits the adenylate cyclases.

Question 4

Be able to describe the activation scheme of a G protein upon receptor binding upon receptor binding.

Answer 4

GPCR receive an input signal

GPCR pefromation conformational change occur, allosterically linked

Now the active G Protein is called GEF, Guanine nucleotide Exchange Factor

The GEF exchange GDP on the alpha subunit for GTP. Causing the alpha subunit to dissociate from the beta and gamma subunits.

Depending on the alpha subunit it can stimulate or inhibitory an effector.

Question 5

True or False

GEF binds to G Protein and causes GTP binding, by adding GTP in the empty alpha subunit of G protein.

To turn off the alpha subunit only GAP, GTPase activating protein can perform GTP hydrolysis.

Answer 5

False, GDP is exchanged for a GTP

False, the alpha subunits are also GTPase.

Question 6

Why are activated GPCRs referred to GEF?

Answer 6

The activated GPCRs are performing the exchange of the Guanine nucleotides (GTP and GDP) in the G protein alpha subunit/