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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: 10308

#Unit 6. System Physiology – Plant

Oxidative decarboxylation of pyruvate to acetyl-CoA by the PDH complex, how the pyruvate dehydrogenase complex carries out the five consecutive reactions in the decarboxylation and dehydrogenation of pyruvate?

 A) Pyruvate reacts with the bound thiamine pyrophosphate (TPP) of pyruvate dehydrogenase, undergoing decarboxylation to the hydroxyethyl derivative

 B) A transesterification in which the —SH group of CoA replaces the —SH group of E2 to yield acetyl-CoA and the fully reduced (dithiol) form of the lipoyl group

 C) The reduced FADH2 of E3 transfers a hydride ion to NAD1 , forming NADH, the enzyme complex is now ready for another catalytic cycle

 D) The transfer of two electrons and the acetyl group from TPP to the oxidized form of the lipoyllysyl group of the core enzyme, dihydrolipoyl transacetylase, to form the acetyl thioester of the reduced lipoyl group

 E) Dihydrolipoyl dehydrogenase promotes transfer of two hydrogen atoms from the reduced lipoyl groups of E2 to the FAD prosthetic group of E3 , restoring the oxidized form of the lipoyllysyl group of E2

 Find out the correct sequence of action of this complex enzyme?
TLS Online TPP Program

#Question id: 10307

#Unit 6. System Physiology – Plant

pyruvate dehydrogenase (PDH) complex requires many enzymes for their functions, which of the following enzyme are not the part of this complex?
TLS Online TPP Program

#Question id: 10306

#Unit 6. System Physiology – Plant

pyruvate dehydrogenase (PDH) complex requires five different coenzymes or prosthetic groups and these enzymesalso require four different vitamins in human nutrition are vital components of this system:
TLS Online TPP Program

#Question id: 10305

#Unit 6. System Physiology – Plant

Pyruvate dehydrogenase complex Consists of three Distinct enzymes and it requires Coenzymes, these are;
TLS Online TPP Program

#Question id: 10304

#Unit 6. System Physiology – Plant

Pyruvate is coverted into the Acetyl-CoA, Acetyl-CoA contain the acetyl group which are comes from the pyruvate and Coenzyme A (CoA) that contain other groups such as;

a) A reactive thiol (—SH) group that is critical to the role of CoA as an acyl carrier in a number of metabolic reactions

b) contain pantothenic acid,  A hydroxyl group of pantothenic acid is joined to a modified ADP moiety by a phosphate ester bond

c) pantothenic acid carboxyl group is attached to β-mercaptoethylamine in amide linkage

d) Hydroxyl group at the 3’ position of the ADP moiety has a phosphoryl group not present in free ADP

which of the following correct observation about Coenzyme A (CoA)?
TLS Online TPP Program

#Question id: 10303

#Unit 6. System Physiology – Plant

During glycolysis, if radiolabelled the glucose at 3 or 4 carbon then what will be the correct prediction about radiolabelling in the cycle?