#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?