38 DNA 複製時常有鹼基錯誤配對發生在新合成股上，細胞中有錯誤配對修復（mismatch repair）的機

制，可除去含有錯誤配對的新合成股（newly synthesized DNA strand），下列何者為此作用的主要酵

素？

 DNA 聚合酶（polymerase β, γ）, DNA 接合酶（ligase）校對系統

 Rec A, Rec F, Rec O, Rec R, SSB 複製系統

 Umu C, Umu D 強制複製（error-prone replication）系統

 Mut H, L, S 複合物辨認系統

ANS D

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39 下列酵素參與由無機物的氮（Inorganic nitrogen）轉變為有機分子（Organic molecule），何者為非？

Arginase  Glutamate dehydrogenase

 Glutamine synthetase  Nitrogenase

ANS A

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34 競爭型抑制劑（competitive inhibitor）會對酵素催化反應之動力學參數，產生何種影響？

 Vmax 降低  Km 值降低  Vmax／Km 值降低  Km 值不變

ANS C

in competitive inhibition:

Vmax remain constant

the affinity of the enzyme to the substrate will be decrease which is represented by a greater value of Km

thus the Vmax/Km is decreased

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in non competitive inhibition

This type of inhibition reduces the maximum rate of a chemical reaction (V_max) without changing the apparent binding affinity of the catalyst for the substrate

result in decrease in Vmax

Km remain constant

Noncompetitive inhibition of an enzyme can occur when an inhibitor binds to an enzyme at a site other than the active site. The noncompetitive inhibitor slows down the reaction rate, i.e. the rate of the product formation is less with inhibitor present than with inhibitor absent. This means that the active site is modified, but not disabled, by the presence of the inhibitor.

As shown in graph #2, the effect of noncompetitive inhibitor cannot be overcome with high substrate concentration. Since the inhibitor and substrate are not competing for the same binding site on the enzyme, a noncompetitive inhibitor reduces the reaction rate at all substrate concentrations.