# Enzyme Technology Questions and Answers – Specificity of Enzyme Action

This set of Enzyme Technology Multiple Choice Questions & Answers (MCQs) focuses on “Specificity of Enzyme Action”.

1. Which of the following is not true for the specificity of enzyme action?
a) Specificity refers to discrimination of an enzyme between two competing substrates
b) Specificity of enzymes lies both the reaction they catalyze and the substrates on which they act
c) Specificity makes it possible for a number of enzymes to coexist in the cell without interfering in each other reaction
d) Five types of specificities have been recognized in enzymes

Explanation: Following statements are true for specificity of enzyme action:
• Discrimination of an enzyme between two competing substrates.
• Enzymes specificity lies in both the reaction they catalyze and the substrates on which they act.
• Because of specificity, it is possible for a number of enzymes to coexist in the cell without interfering in each other reaction.
Not five, but three types of spec specificities have been recognized in enzymes.

2. Which of the following is not a type of specificity?
a) Substrate specificity
b) Reaction specificity
c) Koshland specificity
d) Stereo specificity

Explanation: Specificity refers to discrimination of an enzyme between two competing substrates. They are three types of specificities as given below:
• Substrate specificity, reaction specificity and stereo specificity.
There nothing exists as Koshland specificity. But Koshland induced fit model which explains the enzyme substrate interaction and the rigidity of the active site.

3. Which of the following is not a part of relative substrate specificity?
a) Group specificity
b) Bond specificity
c) Reaction specificity

Explanation: Reaction specificity is one in which the enzyme is specific to a particular reaction, but not substrate and catalyzes only one type of reaction. Substrate specificity is one in which the enzyme acts more than one substrate. Group, Bond and Broad substrate specificity are part of substrate specificity, whereas reaction specificity is not.

4. Which of the following is an example for group specificity?
a) Trypsin hydrolyzing peptide linkages involving arginine or lysine
b) Lipase hydrolyzing ester bond of lipids
c) Hexokinase phosphorylating one or more kind of hexoses
d) L-lactate dehydrogenase will act only on L-lactic acid, and not D-lactic acid

Explanation: Group specificity is one in which an enzyme acts on more than substrate containing particular group. Hence the example which perfectly fits the definition is trypsin hydrolyzing peptide linkages involving arginine or lysine. Lipase hydrolyzing ester bond of lipids is an example for bond specificity. Whereas, Hexokinase phosphorylating one or more kind of hexoses is an example for broad substrate specificity. L-lactate dehydrogenase will act only on L-lactic acid, and not D-lactic acid is an example for stereo specificity.

5. Salivary α-amylase cleaving α(1 → 4) glycosidic bond of carbohydrates is an example for which type of specificity?
a) Group specificity
b) Bond specificity
c) Reaction specificity

Explanation: Bond specificity is one which the enzyme acts on more than substrate containing a particular kind of bond. Hence, Salivary α-amylase cleaving α(1 → 4) glyosidic bond of carbohydrates is an example for bond specificity. The specificity in which an enzyme acts on more than substrate containing particular group is referred to as Group specificity. Reaction specificity is one which the enzyme is specific to a particular reaction, but not substrate and catalyzes only one type of reaction. Broad substrate specificity is one in which the enzyme acts on more than one structurally related substrates.

6. Which of the following is an example for broad substrate specificity?
a) Chymotrypsin hydrolyzing peptide bonds attached to aromatic aminoacids
b) D-glucose oxidase acting only on D-glucose and not L-glucose
c) Hexokinase phosphorylating one or more kind of hexoses
d) Lipase hydrolyzes ester bond of lipids

Explanation: The specificity in which the enzyme acts on more than one structurally related substrates is referred to as broad substrate specificity. The example for this type of specificity is hexokinase phosphorylating one or more kind of hexoses which include glucose, mannose fructose etc.

7. What is represented in the following diagram?

a) Reaction specificity
b) Substrate specificity
d) Stereo specificity

Explanation: In the above diagram, an example for reaction specificity is shown. The type of specificity in which the enzyme is specific to a particular reaction, but not substrate and catalyzes only one type of reaction is referred to reaction specificity. As shown in the diagram, pyruvate can undergo several reactions. But each reaction is catalyzed by a separate enzyme, which catalyzes only that reaction and none other. Hence it is a perfect example for reaction specificity.

8. Which of these is not an example for stereo specificity?
a) L-lactate dehydrogenase will act only on L-lactic acid, and not D-lactic acid
b) D-glucose oxidase acting only on D-glucose and not L-glucose
c) L-amino oxidase acts only on L-amino acids and not D-aminoacids
d) Hexokinase phosphorylating one or more kind of hexoses

Explanation: Hexokinase phosphorylating one or more kinds of hexoses is an example for broad substrate specificity and not stereo specificity. Stereo specificity is referred to as enzymes showing specificity towards only one type of isomers. Hence the examples for stereo specificity are as follows:
• L-lactate dehydrogenase will act only on L-lactic acid, and not D-lactic acid.
• D-glucose oxidase acting only on D-glucose and not L-glucose.
• L-amino oxidase acts only on L-amino acids and not D-aminoacids.

9. L-lactate dehydrogenase: L-lactic acid:: Salivary α-amylase: __________
a) D-aminoacid
b) L-aminoacid
d) D-glucose

Explanation: The type of specificity in which the enzymes is showing specificity towards only one type of isomers is referred to as stereo specificity. L-lactate dehydrogenase shows stereo specificity to L-lactic and not D-lactic acid. In the same way, salivary α-amylase acts on α- 1,4 glycoside linkage and is inactive on β-1,4 glycoside linkage.

10. Which of the following do not show stereo specificity?
a) L-lactate dehydrogenase
b) Epimerase
c) Salivary α-amylase
d) L-glucose oxidase

Explanation: Stereo specificity is one in which the enzymes shows specificity towards only one type of isomers. L-lactate dehydrogenase, Salivary α-amylase and L-glucose oxidase shows stereo specificity toward L-lactic acid, α- 1,4 glycoside linkage and L-glucose respectively. Epimerase and isomerase do not show stereo specificity.

11. Which type of specificity is represented in the following reaction?
Glucose $$_{\overrightarrow{Glucokinase}}$$ Glucose-6-phosphate
a) Relative substrate specificity
b) Absolute substrate specificity
d) Stereo specificity

Explanation: Absolute substrate specificity is one in which the enzymes will act on only substrate and catalyze only one reaction. Thus, glucose converted to glucose 6 phosphate by glucokinase is an example for absolute specificity. Relative substrate specificity is one in which the enzyme acts on more than one substrate. Broad substrate specificity is one in which the enzyme acts on more than one structurally related substrates. The specificity in which the enzymes show specificity towards only one type of isomers is known as stereo specificity.

12. Which of the following is not an example of absolute substrate specificity?
a) Glucose to glucose-6-phosphate by glucokinase
b) Hexokinase phosphorylating one or more kind of hexoses
c) Lactose to glucose and galactose by lactase
d) Urea to ammonia by urease

Explanation: The specificity in which the enzymes will act on the only substrate and catalyze only one reaction is referred to as absolute substrate specificity. Examples for such type of specificity are as follows:
• Glucose to glucose-6-phosphate by glucokinase
• Lactose to glucose and galactose by lactase
• Urea to ammonia by urease
Hexokinase phosphorylating one or more kind of hexoses is an example for broad substrate specificity, which means the enzyme acting on more than one structurally related substrates.

Sanfoundry Global Education & Learning Series – Enzyme Technology.