Tumor-suppressor genes generally encode proteins that in one way or another inhibit cell proliferation. Loss-of-function mutations in one or more of these proliferation inhibitory proteins contribute to the development of many cancers. Prominent among the classes of proteins encoded by tumor-suppressor genes are:

A. Intracellular proteins that regulate or inhibit entry into the cell cycle

B. Receptors or signal transducers for secreted hormones or developmental signals that inhibit cell proliferation

C. Checkpoint pathway proteins that arrest the cell cycle if DNA is damaged

D. Proteins that promote apoptosis

Following genes belongs to the above class-

i. p53

ii. Rb

iii.TGF- β

iv. Caspase 3 and 7

which of the following match 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: 642

#Unit 1. Molecules and their Interaction Relevant to Biology

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: 641

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following does NOT describe a mechanism that cells use to regulate enzyme activities?

A. Cells control enzyme activity by phosphorylation and dephosphorylation.

B. Cells control enzyme activity by the binding of small molecules.

C. Cells control the rates of diffusion of substrates to enzymes.

D. Cells control the rates of enzyme degradation.

E. Cells control the rates of enzyme synthesis.

F. Cells control the targeting of enzymes to specific organelles. 

#Question id: 640

#Unit 1. Molecules and their Interaction Relevant to Biology

The data in the table above were collected for an enzyme-catalyzed reaction. The Km for this enzyme is approximately

#Question id: 639

#Unit 1. Molecules and their Interaction Relevant to Biology

Match the coenzymes in column I enzymes to class of enzymes in column II

#Question id: 638

#Unit 1. Molecules and their Interaction Relevant to Biology

Match the following class of enzymes with them