Mitotic CDK complexes are maintained in an inactive state through inhibitory phosphorylation of the CDK subunit. Two highly conserved tyrosine and threonine residues in mammalian CDKs are subject to regulated phosphorylation.

Gene	Mutant phenotypes
A. Wee1	i. the cell does not divide but continues to grow
B. CAK kinase	ii. mitotic cyclins are inactivated
C. cdc25 phosphatase	iii. premature entry into mitosis

The following table enlists genes and phenotypes observed on mutation of these genes but not correctly matched. Which one of the following combinations is correctly matched ?

#Question id: 626

#Unit 1. Molecules and their Interaction Relevant to Biology

A metabolic pathway proceeds according to the scheme, R -> S -> T -> U -> V -> W.  A regulatory enzyme, X, catalyzes the first reaction in the pathway.  Which of the following is most likely correct for this pathway?

#Question id: 625

#Unit 1. Molecules and their Interaction Relevant to Biology

For enzymes in which the slowest (rate-limiting) step is the reaction Km becomes equivalent to:

#Question id: 624

#Unit 1. Molecules and their Interaction Relevant to Biology

The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics: The Km for this enzyme is approximately:

#Question id: 623

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of these statements about enzyme-catalyzed reactions is false?

#Question id: 622

#Unit 1. Molecules and their Interaction Relevant to Biology

An enzyme-catalyzed reaction was carried out with the substrate concentration initially a thousand times greater than the Km for that substrate.  After 9 minutes, 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 12 micromol.  If, in a separate experiment, one-third as much enzyme and twice as much substrate had been combined, how long would it take for the same amount (12 micromol) of product to be formed?

#Question id: 621

#Unit 1. Molecules and their Interaction Relevant to Biology

Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by the expression: