This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Targets – Engineering Specificity and Purification”.
1. Protein engineering cannot be used to do which of the following changes?
a) Tuning of enzyme specificity
b) Introduction of novel properties
c) Introduction of regulatory sites or switches
d) Completely change the specificity of an enzyme
View Answer
Explanation: Protein engineering cannot be used to completely change the specificity of an enzyme. Protein engineering can be used for tuning of enzyme specificity, the introduction of novel properties, and the introduction of regulatory sites or switches.
2. Binding sites for metal ions often prove useful to regulate enzyme activity.
a) False
b) True
View Answer
Explanation: The above statement is true. Binding sites for metal ions often prove useful to regulate enzyme activity. Thus, the introduction of a binding site for Ca+2 is sufficient to allow regulation of trypsin activity.
3. Which of the following is an important issue for the production of industrial recombinant proteins?
a) Obtain fragments of proteins
b) Obtain the protein in the desired location
c) Obtain the whole protein molecule
d) Obtain proteins in pure and active form
View Answer
Explanation: Obtaining proteins in pure and active form is an important issue for the production of industrial recombinant proteins. Obtaining fragments of proteins, protein in the desired location, and whole protein molecule are not important issues for the production of industrial recombinant proteins.
4. Cofactor requirements cannot be altered by mutagenesis.
a) True
b) False
View Answer
Explanation: The above statement is false. Cofactor requirements can be altered by mutagenesis. There is a case where researchers have changed the dependence of E. coli isocitrate dehydrogenase from NADP to NAD by replacing amino acids in the adenosine-binding pocket.
5. Which of the following aids in the purification of recombinant proteins?
a) Introduction of “gaps”
b) Introduction of “random cuts”
c) Introduction of “mutations”
d) Introduction of “Tags”
View Answer
Explanation: The Introduction of “Tags” aids in the purification of recombinant proteins. Introduction of “gaps”, “random cuts”, and “mutations” does not aid in the purification of recombinant proteins. Tags help the recombinant proteins to segregate from the other unwanted proteins.
6. Alignment of sequences of homologous enzymes with different specificities as well as structural information has proven useful as a guide to identifying residues possibly involved in the enzyme-substrate specificity.
a) False
b) True
View Answer
Explanation: The above statement is true. Alignment of sequences of homologous enzymes with different specificities as well as structural information has proven useful as a guide to identifying residues possibly involved in the enzyme-substrate specificity. These sequences can help us in the process of protein engineering to modify the specificity of an enzyme.
7. Only specific molecules can serve as substrates for a specific enzyme.
a) False
b) True
View Answer
Explanation: The above statement is true. Only specific molecules can serve as substrates for a specific enzyme because the substrate must fit into the active site of the enzyme before catalysis can occur. In many cases, an enzyme will react with only one naturally occurring molecule.
8. Which of the following is essential to keep separate the many pathways involving hundreds of enzymes, that function during metabolism?
a) Enzyme quantity
b) Enzyme concentration
c) Enzyme purity
d) Enzyme specificity
View Answer
Explanation: Enzyme specificity is essential to keep separate the many pathways involving hundreds of enzymes, that function during metabolism. Enzyme quantity, enzyme concentration, and enzyme purity are not essential to keep separate the many pathways involving hundreds of enzymes, that function during metabolism.
9. All enzymes are highly specific.
a) True
b) False
View Answer
Explanation: The above statement is false. Not all enzymes are highly specific. Digestive enzymes such as pepsin and chymotrypsin, for example, can act on almost any protein. Thus, these enzymes are not highly specific.
10. All enzymes isolated thus far are specific for the type of chemical reaction they catalyze.
a) False
b) True
View Answer
Explanation: The above statement is true. All enzymes isolated thus far are specific for the type of chemical reaction they catalyze i.e. oxidoreductases do not catalyze hydrolysis reactions, and hydrolases do not catalyze reactions involving oxidation and reduction.
11. Which of the following represents the correct schematic of enzymatic reactions?
a) Enzyme-Product release → enzyme-substrate binding → catalysis
b) Enzyme-Product release → catalysis → enzyme-substrate binding
c) Catalysis → enzyme-substrate binding → enzyme-Product release
d) Enzyme-substrate binding → catalysis → enzyme-Product release
View Answer
Explanation: The correct schematic of enzymatic reactions is ‘enzyme-substrate binding → Catalysis → Enzyme-Product release’. An enzyme attracts substrate to its active site, catalyzes the chemical reaction by which products are formed, and then allow the products to dissociate (separate from the enzyme surface).
12. Which of the following represents a ternary complex?
a) A complex of three enzymes
b) A complex of three substrates
c) A complex of two enzymes and one substrate
d) A complex of one enzyme and two substrates
View Answer
Explanation: Complex of one enzyme and two substrates represents a ternary complex. A complex of one enzyme and one substrate is called a binary complex. A complex of three enzymes, a complex of three substrates, or complex of two enzymes and one substrate do not represent a ternary complex.
13. Which among the following is highly specific?
a) Pepsin
b) DNase
c) Chymotrypsin
d) Thrombin
View Answer
Explanation: Thrombin is a highly specific protein. It reacts only with the protein fibrinogen. It is a part of a very delicate blood-clotting mechanism and thus must act only on one compound to maintain the proper functioning of the system. Pepsin, DNase, and chymotrypsin are not highly specific enzymes.
14. The substrates are attracted to the active site by which of the following interactions?
a) Covalent and Vander Waal’s interactions
b) Hydrophobic and covalent interactions
c) Vander Waal’s interactions only
d) Electrostatic and hydrophobic forces.
View Answer
Explanation: The substrates are attracted to the active site by electrostatic and hydrophobic forces. These are physical interactions and not chemical bonds. Covalent and Vander Waal’s interactions do not prominently help in the attachment of the substrate to the active site of the enzyme.
15. The rate of enzymatic reactions is studied by which of the following curves?
a) Reactivity curve
b) Monod curve
c) Stability curve
d) Michaelis-Menten curve
View Answer
Explanation: The rate of enzymatic reactions is studied by the Michaelis-Menten curve. The curve obtained in most cases is a hyperbola. Reactivity curve, Monod curve, and stability curve do not help in the study of the rate of enzymatic reactions.
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