20. The Km is a. The time for half of the substrate to be converted to product b

Question

20. The Km is a. The time for half of the substrate to be converted to product b. The time for all of the substrate to be converted to product C. The [S] that gives half of the maximum reaction rate d. The [S] that gives the maximum reaction rate e. The [P] that is produced when the enzyme is saturated with the substrate 21. Which of the following statements is true about non-competitive inhibition? a. Km increases b. Km decreases C. Vmax increases d. Vmax decreases e. Vmax and Km decrease 22. Which of the following statements best characterizes our concept of an antibody? An antibody contains high molecular weight RNA as its basic structure. An antibody is composed of four identical protein subunits which may be caused to dissociate by a. b. treatment with urea. An antibody contains protein as its major chemical component and its synthesis may be induced by the administration of a foreign protein or polysaccharide An antibody contains polysaccharide as its major chemical component and the synthesis of these may be elicited by the administration of a foreign protein or polysaccharide. c. d.

Explanation / Answer

Ans. #20. Correct option- C. The [S] that gives half of the maximum reaction rate.

# MM equation:        Vo = Vmax [S] / ([S] + Km)

At half-Vmax, Vo = 0.5 Vmax

            Or, 0.5 Vmax = Vmax [S] / ([S] + Km)

            Or, 0.5 Vmax / Vmax = [S] / ([S] + Km)

            Or [S] + Km = 2 [S]

            Or, Km = 2 [S] – [S]

            Hence, Km = [S]                    - when Vo = ½ Vmax

Therefore, Km is defined as the [S] at which half-Vmax is attained.

#21. Correct option – d. Vmax decreases.

# A mixed inhibition lead to decrease in both Vmax and Km by different factors (a and a’ ).

Non-competitive inhibition is a special case of mixed inhibition where Km remains unaffected.

# So, In case of Non-competitive inhibition, Vmax decreases but Km remains unaffected.

# In an uncompetive inhibition, both Vmax and Km decrease by same factor (a).

#22. Correct option- C. An antibody has protein as its major chemical component. It consists of 4 peptide chains – 2 similar heavy chains, and 2 similar light chains. The immune system triggers the synthesis of antibody when stimulated by antigens (foreign proteins or polysaccharides).

# An antibody is not constituted of RNA, polysaccharides. It neither is constituted of four identical protein subunits.

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