Following process and their mechanism during fertilization in mammals.

a. Rheotaxis	i.A sensing mechanism in which, the oocyte and its accompanying cumulus cells secrete molecules that attract capacitated sperm toward the egg during the last stages of sperm migration
b.  Chemotaxis	ii.It is a transient event, and sperm are given a relatively brief window of competence during which they can successfully fertilize the egg.
c.  Capacitation		iii.it is the ability to sense temperature difference and preferentially swim from cooler to warmer sites is found only in capacitated sperm.
d. Thermotaxis		iv.Sperm receive long-distance directional cues from the flow of liquid from the oviduct to the uterus and they will migrate against the direction of the flow—using CatSper calcium channels to sense calcium influx and monitor the direction of the current

Which of the following option is correct?

#Question id: 643

#Unit 1. Molecules and their Interaction Relevant to Biology

The hydrolysis of lactose is catalysed by b-galactosidase as given below

Which of the following could be correct mechanism for this hydrolysis reaction?

A. Nucleophilic attack by the carboxylate group of Glu/Asp on the C-1 carbon atom of the galactose moiety within glucose, releasing glucose and forming an intermediate with the galactose linked to the enzyme through an ester linkage. Water then attacks this carbon atom, displacing the glutamate carboxylate and releasing galactose.

B. Electrophilic attack by the carboxylate group of Glu/Asp on the C-1 carbon atom of the galactose moiety within glucose, releasing glucose and forming an intermediate with the galactose linked to the enzyme through an ester linkage. Water then attacks this carbon atom, displacing the glutamate carboxylate and releasing galactose.

C. Nucleophilic attack by the carboxylate group of Lys/Arg/His or bivalent cation on the C-1 carbon atom of the galactose moiety within glucose, releasing glucose and forming an intermediate with the galactose linked to the enzyme through an ester linkage. Water then attacks this carbon atom, displacing the glutamate carboxylate and releasing galactose.

#Question id: 644

#Unit 1. Molecules and their Interaction Relevant to Biology

Enzyme X and Enzyme Y are both involved in monosaccharide metabolism. Enzyme X uses glucose as a substrate while Enzyme Y uses fructose as a substrate. At pH=7.0, Enzyme X has a Vmax of 10 μM/s while Enzyme Y has a Vmax of 20 μM/s. Both enzymes have a Km of 3.0 mM for their respective substrates. Which aspects of its reaction will be changed by Enzyme Y?

#Question id: 645

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following is the correct combination of marker enzymes used to identify different organelles during subcellular fractionation of eukaryotic tissue?

#Question id: 646

#Unit 1. Molecules and their Interaction Relevant to Biology

Many biosynthetic pathways are regulated by feedback inhibition of enzymes. In a particular type of feedback inhibition, two endproducts individually do not inhibit an enzyme upstream in the pathway at all, but when both are present they inhibit the same enzyme significantly. What type of feedback inhibition do these inhibitors represent?

#Question id: 647

#Unit 1. Molecules and their Interaction Relevant to Biology

For the hypothetical reversible reaction where S is converted to P, the rate constant for the forward reaction is 10⁵ s^-1 while that of the backward reaction is 10¹ s_-1. If the reaction is catalyzed by an enzyme, the rate constant for the forward reaction increases 100-fold. What will be the equilibrium constant of the enzyme catalyzed reaction?

#Question id: 648

#Unit 1. Molecules and their Interaction Relevant to Biology

Enzyme catalysis is regulated by a number of mechanisms. Also, the flux through metabolic pathways must be regulated. Given the metabolic pathway below, which choice accurately describes the regulation of compound G levels?