Over long periods of time, many cave-dwelling organisms have lost their eyes. Tapeworms have lost their digestive systems. Whales have lost their hind limbs. How can natural selection account for these losses?

#Question id: 642

#Unit 1. Structure and Function of Biomolecules

The graphs P, Q and R show the variation of rate constant (k) with temperature. The reactions represented by P, Q and R, respectively, are

#Question id: 643

#Unit 1. Structure and Function of Biomolecules

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. Structure and Function of Biomolecules

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. Structure and Function of Biomolecules

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. Structure and Function of Biomolecules

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. Structure and Function of Biomolecules

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?