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#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: 7269

#Unit 5. Developmental Biology

Following statements are regarding to gastrulation in chick embryo.

A. During gastrulation, future mesodermal and endodermal cells migrate from the epiblast through the primitive streak into the interior of the blastoderm.

B. An aggregation of cells, known as Hensen’s node, forms at the posterior end of the streak.

C. As the streak extends, cells of the epiblast move toward the primitive streak, through it, and then outward again underneath the surface to give rise internally to the mesoderm and endoderm, the latter displacing a lower layer of cells called the endoblast.

D. Cells that remain in the epiblast form the endoderm.

Which of the following statements are correct?
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#Question id: 7268

#Unit 5. Developmental Biology

Match the columns and choose the correct option.

Column I           

Column II

A.    Progress zone

i.                    thickening of the ectoderm at the apex of the developing limb bud

 

B.     Apical ectodermal ridge

ii.                  The cells found within the most posterior region

C.     Zone of polarizing activity

iii.                The highly proliferative mesenchyme that fuels limb bud growth


TLS Online TPP Program

#Question id: 7267

#Unit 5. Developmental Biology

Endocrine disruptors can interfere with hormone function in many ways like, They can act as antagonists and inhibit the binding of a hormone to its receptor or block the synthesis of a hormone. which of the following example best explains the antagonistic effect of endocrine disruptors?
TLS Online TPP Program

#Question id: 7266

#Unit 5. Developmental Biology

After brief examination of the evolution of the tetrapod limb, from fish fins to human hands, has hopefully illuminated the importance of Hox gene regulation during limb development. Hox genes are critical for:
TLS Online TPP Program

#Question id: 7265

#Unit 5. Developmental Biology

Following statement regarding to the cascade of regulated RNA splicing controls drosophila sexual differentiation.

A. The Sex-lethal (Sxl) protein, encoded by the sex-lethal gene, is the first protein to act in the cascade and present only in female embryos.

B. Early in development, the Sxl gene is transcribed from a promoter that functions only in male embryos.

C. Later in development, this male-specific promoter is shut off, and another promoter for sex-lethal becomes active in both male and female embryos.

D. In male embryos, however, in the absence of early Sxl protein, exon 3 of the sex-lethal pre-mRNA is spliced to exon 2 to produce an mRNA that contains a stop codon early in the sequence.

Which of the following is correct?
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#Question id: 7264

#Unit 5. Developmental Biology

The Dictyostelia social amoebas are found in a wide range of soil habitats. They can come together to form a fruiting structure, in which a proportion of cells are sacrificed to build the stalk and the remainder differentiate into resilient dormant spores. This multicellular life cycle is common to all Dictyostelids. It consists of an interconnected programme of cell movement and cell differentiation, and has been intensively studied in the model organism D. discoideum. Few mutants (Column A) and phenotypes (Column B) are listed in the table given below.

    Column A

    Column B

A. Loss of function of cAMP-dependent protein kinase (PKA)

i. cell develop normally but unable to germinate

B. Loss of function of RegA

ii. Loose aggregate form

C. Loss of function of adenylate cyclase B

iii. No aggregation

D. Loss of function of gp80

iv. accumulation of cAMP and PKA activation

 Match the correct mutant with the observed phenotype.