Question

82) When TGFbeta binds to which partner in its receptor complex first?

- RI

- RII

- RIII

- RIV

87) Binding of cytokine to its extracellular receptor engages which of the following signaling pathways?

- JAK/STAT

- Ras/MAP kinase

- PI-2 kinase

- TGFbeta

93) The internal compartment of an endosome is acidified by the presence of ______.

- acid hydrolases

- K+ pumps

- H+ ATPases

- vSNARES

95) When a RTK has dimerized & is active, how many ligands are bound?

- 1

- 2

- 3

- 0

Answer 1

82 ) Option B i.e , RII is correct.

TGF -beta are family of secreted cytokines that regulate a collection of diverse biological response including cell proliferation, differentiation and survival. TGF-beta signalling pathway start with when TGF-Beta (ligand) binds with the receptor on the cell. It binds with first with RII and bring together RII and RI on the cell surface.This receptor are serine/threonine kinases.This interaction of the receptor lead to phosphorylation of RI kinase domain by RII, which then propagates the signal through phosphorylation of smad protein and then further downstream process.

87) Option A i.e , JAK/STAT is correct.

Binding of cytokine to extracellular mainly engages JAK/STAT pathway .Binding of cytokine leads to pathway activation by changes in the receptor that allow the intracelluar JAKs associated ( domain in the receptor) to phosphorylate each other.This pathway is mainly involved in processes like immunity where cytokines play a major role in maintaining immune homeostasis. But in the other pathways mentioned mainly the ligands are growth factor which help in the cellular growth and differentiation.

93) Option C i.e, H+-ATPase is correct .

The internal compartment of an endosome is acidified by the presence of H+ -ATPase. The H+ ATPase are large , complex proton pumps that act as a transmembrane pore for protons. The lumenal pH of endosomes are acidic .Endosome have a pH in the range of 6.8-6.1 .The low pH or acidic environment provides a better environment for hydrolytic reactions which are essential for membrane trafficking . This  acidic environment is regualted by adjustment of H+ATPase concentration in the membrane .

95) Option B i.e ,1 is correct.

When a RTK has dimerized & is active, one ligand is  bound. RTK functions when ligand is bound to RTK and it dimerize and then downstream signalling occurs and also when the first the RTK will dimerize and then it will bind to the ligand and then downstream signalling occurs. In the second case where RTK dimerize means there are two receptor so there should be two ligand binding pocket and two ligand will be able to bind it ,but thats not the case,dimerization lead to conformational change in the ligand binding pocket and now it can bind to only one ligand of that conformation and then operate the further downstream process.