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TLS Online TPP Program

#Question id: 1249

As in all G protein–coupled signalling pathways, timely termination of the rhodopsin signalling pathway requires that all the activated intermediates be inactivated rapidly, restoring the system to its basal state, ready for signalling again. Which of the following mechanism does not terminate rhodopsin signalling?

#Unit 4. Cell Communication and Cell Signaling

  1. The complex composed of the inhibitory γ subunit of PDE and Gαt∙ GTP recruits two additional proteins, RGS9 and Gβ5, that together act as a GAP to enhance the rate of hydrolysis of bound GTP to GDP. Hydrolysis of GTP, in turn, causes release of the PDE γ subunit, which re-joins the PDE α and β subunits, terminating PDE activation.

  2. Light-triggered closing of the cGMP-gated cation channels causes a drop in the cytosolic Ca2+ concentration inside the rod cell. The drop in the intracellular Ca2+ concentration is sensed by a class of Ca2+-binding proteins known as guanylate cyclase–activating proteins, which bind to guanylate cyclase and stimulate its activity, thereby elevating the level of cGMP and causing the cGMP-gated ion channels to reopen.

  3. A major process that suppresses and helps to terminate the visual response involves phosphorylation of rhodopsin when it is in its activated (R*). Rhodopsin kinase, is the enzyme that catalyzes this phosphorylation reaction. Arrestin bound to the phosphorylated R* completely prevents interaction with Gαt, blocking formation of the active Gαt∙ GTP complex and stopping further activation of PDE.

  4. Binding of acetylcholine triggers activation of the Gαi subunit and its dissociation from the Gβγ subunit in the usual way. In this case, however, the released Gβγ subunit (rather than Gαi∙ GTP) binds to and opens the associated effector protein, a K+ channel. The increase in K+ permeability hyperpolarizes the membrane, which reduces the frequency of PDE activation.

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TLS Online TPP Program

#Question id: 5130

#Unit 5. Developmental Biology

Regulation by gradients of paracrine factor concentration was elegantly demonstrated by the specification of different mesodermal cell types in the frog Xenopus laevis by activin, a paracrine factor of the TGF-beta family. Which of the following observations are correct from this graph?
TLS Online TPP Program

#Question id: 5131

#Unit 5. Developmental Biology

Differentiated cells express the genes and proteins characteristic of their final identity in the adult, and that identity can be altered only under special circumstances. How does the concept of differentiation, as described here, differ from the concept of determination?
TLS Online TPP Program

#Question id: 5132

#Unit 5. Developmental Biology

Upon secretion of wnt, When Wnt attaches to the Frizzled receptor on a responding cell, the cell secretes Notum, a hydrolase that associates with glypican and then cleaves off Wnt’s attached lipids in a process of deacylation or delipidation. This process:
TLS Online TPP Program

#Question id: 5133

#Unit 5. Developmental Biology

Identify the correct ligands in both receptor serine kinase pathway.

 
TLS Online TPP Program

#Question id: 5134

#Unit 5. Developmental Biology

Match the following cleavage patterns with the species in which they occur.

SpeciesCleavage Pattern
A. Flatwormi. Meroblastic discoidal
B. Frogii. Meroblastic superficial
C. Birdsiii. Holoblastic displaced radial
D. Insectiv. Holoblastic spiral
TLS Online TPP Program

#Question id: 5135

#Unit 5. Developmental Biology

In xenopus, result of tissue transplantation during early and late gastrulae

(A) Cells of early newt gastrula exhibit conditional development.

(B) Cells of early newt gastrula exhibit autonomous development

(C) Cells of late newt gastrula exhibit conditional development.

(D) Cells of late gastrula exhibit autonomous development.

The correct inferences are: