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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: 7191

#Unit 5. Developmental Biology

In tunicate embryo, Presumptive endoderm originates from the vegetal A4.1 and B4.1 blastomeres. The specification of these cells coincides with the localization of β-catenin. Which of the following statement is incorrect?
TLS Online TPP Program

#Question id: 7192

#Unit 5. Developmental Biology

The following are statements regarding the development and maintenance of anterior and posterior compartments in each segment of Drosophila. Which of the following is correct?
TLS Online TPP Program

#Question id: 7193

#Unit 5. Developmental Biology

Some statements with respect to the regeneration in hydra.

A. The major head inducer of the hypostome organizer is a set of Wnt proteins acting through the canonical B-catenin pathway.

B. The major head inducer of the hypostome organizer is a set of Wnt proteins acting through the noncanonical B-catenin pathway.

C. These Wnt proteins are seen in the apical end of the early bud, defining the hypostome region as the bud elongates

D. If the Wnt signaling inhibitor GSK3 is itself inhibited throughout the body axis, ectopic tentacles form at all levels, and each piece of the trunk has the ability to stimulate the outgrowth of new buds.

E. transgenic hydra made to globally misexpress the downstream Wnt effector ectopic tentacles form at all levels, and each piece of the trunk has the ability to stimulate the outgrowth of new buds.

Which of the following statements are incorrect?
TLS Online TPP Program

#Question id: 7194

#Unit 5. Developmental Biology

Formation of digits and sculpting the tetrapod limb requires death of specific cells in the limb in a programmed manner. Which one of the following interactions could explain proper limb formation?
TLS Online TPP Program

#Question id: 7195

#Unit 5. Developmental Biology

Given below are some of the statements regarding toll signalling pathway in drosophila.

A. Dorsal protein is a transcription factor with homology to the Rel/nuclear factor kappa B (NFκB) family of vertebrate transcription factors, which are involved in regulation of gene expression in vertebrate immune responses.

B. Toll signalling pathway is also used in the adult fly in defense against infection.

C. In the Drosophila embryonic Toll pathway Dorsal is held inactive in the nucleus by the protein Cactus.

D. The ligand for Toll is a fragment of the protein Easter, which is generated in the ventral vitelline space by the protease Spatzle.

E. When Toll is activated by binding the Spätzle fragment, its cytoplasmic domain binds a complex of the adaptor proteins dMyD88 and Tube. Tube interacts with, and activates, the protein kinase Pelle.

F. Activation of Pelle leads to the dephosphorylation of Cactus. This releases Dorsal, which is then free to enter a nucleus.

Choose the most appropriate combination of correct statements:
TLS Online TPP Program

#Question id: 7196

#Unit 5. Developmental Biology

Under the process of endochondral ossification-