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TLS Online TPP Program

#Question id: 3783

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?

#Unit 3. Fundamental Processes

  1. The origins of replication occur only at the 5′ end.

  2. Helicases and single-strand binding proteins work at the 5′ end.

  3. DNA polymerase can join new nucleotides only to the 3′ end of a pre-existing strand, and the strands are antiparallel.

  4. DNA ligase works only in the 3′ → 5′ direction.

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TLS Online TPP Program

#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.
TLS Online TPP Program

#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?
TLS Online TPP Program

#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?
TLS Online TPP Program

#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?
TLS Online TPP Program

#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?
TLS Online TPP Program

#Question id: 648

#Unit 1. Structure and Function of Biomolecules

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?