Question

For the following questions, multiple answers may apply.

1) Enzyme activity in cells is controlled by which processes:

a) covalent modifications

b) modulation of expression levels

c) feedback inhibition

d) binding to allosteric effectors

2) Which of the following statements about the concept of “induced fit” are true (2pts):

a) Substrate binding induces either global or local conformational change in the

enzyme, which then brings catalytic groups into proper orientation.

b) When a substrate binds to an enzyme, the enzyme induces a loss of water fromthe substrate.

c) Enzyme-substrate binding induces an increase in the reaction enthalpy, therebycatalyzing the reaction.

d) In induced fit, binding of a substrate to the enzyme uses the same types of interactions formed in the 'lock and key' model.

3) Derivation of the Michaelis-Menten equation includes which of the following assumptions?

a) product concentration exceeds enzyme concentration - [P]>>>[E]

b) substrate and product are at equal concentrations - [S] = [P]

c) the enzyme•substrate complex concentration [ES] is constant

d) substrate falls out of the active site faster than catalysis - k–1>>k2

Answer 1

Q. 1

Ans: enzymatic activity is controlled by several factors including covalent modification, modulation of expression level of ezyme at genetic level and post translational level, feed back inhibition and action of regulatory molecules such as allosteric effectors and inhibitors.

Covalent modification enables the formation of enzyme subsratr complex(ES) leads to the production of product/products.

Modulation of expression level at genetic level is governed by regulatory molecules such as activators and inhibitors known as pretransrcriptional regulation.

Modulation of enzymatic activity at Post translational level includes post translational modification of enzymes like phosphorylation/dephoshorylation/ADP ribosylation etc.

Feed back inhibition refers to inhibition enzyme catalysed pathway by inhibiting the key enzyme of pathway by end product. It is commonly exhibited by allosteric enzymes.

Allosteric regulatory molecules may be inhibitors or may be activators or enhancers. Inhibitors inhibit enzymatic activity by imparting a change in active site so that the substrate cannot bind there whereas enhancers modify the active site in such a way that which enables the firm attachment substrate to the active site.

Q. 2

Ans: The induced-fit model, proposed by Daniel Koshland in 1958, attempts to explain how this is accomplished. His theory asserts that when the active site on the enzymes makes contact with the proper substrate, the enzyme molds itself to the shape of the molecule. It is just like how our palm and fingers fit inside a gloves. As per induced model the confirmation of active site is not predetermined whereas it is predetermined in Lock and Key model proposed by Fisher.

Q. 3

Ans: both (b) and (c) are correct

The amount of product formed will be proportional to substrate concentration until all the enzymes are get

saturated with substrate then remain constant. Km is the substrate concentration required to produce half the maximum velocity.

When Vi=1/2Vmax

Then Km= [s] ie substrate concentration.