Question

1- Which of the following statements is correct concerning receptor tyrosine kinases?

contain unusual amounts of tyrosine

dissociates from the membrane after binding its ligand

can auto-phosphorylate on the cytoplasmic domain when activated

is a seven transmembrane-helix receptor

always associated with a G-protein

2- Which of the following statements is correct about G-proteins?

G-proteins can affect adenylate cyclase activity.

G-proteins are integral membrane proteins.

G-proteins bind to receptor tyrosine kinases.

G-proteins bind hormones.

G-proteins are homodimers.

Answer 1

Ans1: The correct statement is:

can auto phosphorylate on the cytosolic domain when activated (Ligand binding on the extracellular domain containing ligand binding site, causes a conformational change that promotes formation of a functional dimeric receptor, bringing together two intrinsic or associated kinases & leading to activation of intrinsic protein kinase activity of receptor & causing autophosphorylation of tyrosine residues in its cytosolic domain side)

Ans2 : The correct option is :

G- proteins can affect adenylate cyclase activity (The G - proteins are involved in activation of adenylate cyclase enzyme, hence they are also called as stimulatory G- protein/Gs. The alpha subunit of Gs proteins binds with other subunits in response to receptor & hydrolyzes GTP & activates plasma - membrane bound enzyme adenylate cyclase, which synthesizes cAMP from ATP.

Incorrect options explaination :

* G - proteins are a part of cell surface receptors ( GPCR).

* G - protein are coupled to their own receptors called G protein coupled receptors(GPCRs)

* GPCRs receptor site binds to hormones not the G - proteins binds directly to receptors. They only are regulated by the binding of hormones to receptors, not binds with the receptors itself.

* G - proteins are heterodimers containing alpha, beta & gamma subunits.

Hope this will help you?