250+ TOP MCQs on Isolation of Enzymes and Answers

Enzyme Technology Multiple Choice Questions on “Isolation of Enzymes”.

1. _________________ is the main contaminant present in the resultant free extract from cells.
A. Chemicals
B. Simple sugars
C. Lipids
D. Nucleic acids
Answer: D
Clarification: The resultant cell free extract obtained from extraction procedures possess nucleic acids, lipids, simple sugars and so on. But nucleic acid is the major contaminant and care should be taken to remove it from the system.

2. Enzymes can be isolated from cell free extract by which one of the following methods?
A. Osmotic shock
B. Alkali treatment
C. Factors like pH, temperature and low ionic strength
D. Ultrasonication
Answer: C
Clarification: Osmotic shock, Alkali treatment and ultrasonication are the methods used to extract enzymes from cells. Osmotic shock and alkali treatment is included in extraction by chemical methods as these methods use 1.4% buffered sucrose and NaOH respectively. Ultrasonication utilizes ultrasonic waves fall into physical treatment category. Hence enzymes can be isolated from cell free extracts using factors like pH, temperature and low ionic strength.

3. Which of the following methods cannot be used to isolate enzymes from cell free extract?
A. Use of factors like pH and ionic strength
B. Use of chemicals
C. Homogenization
D. Use of temperature factor.
Answer: C
Clarification: Nucleic acid is the major contaminant in the cell free extract along with lipids, simple sugars and so on. Factors like temperature, pH and ionic strength can be used to remove the contaminants and isolate enzymes. Chemicals such as streptomycin sulphate, nucleases etc., can be used to degrade nucleic acids and isolate the required enzymes.

4. Which one if the chemicals is not used to isolate enzymes from cell free extract?
A. 1.4% buffered sucrose
B. Cetyl trimethyl ammonium bromide
C. Nucleases
D. Streptomycin sulphate
Answer: A
Clarification: 1.4% buffered sucrose is the chemical used during osmotic shock which is a chemical method to extract enzymes from cells. Whereas cetyl trimethyl ammonium bromide, nucleases, streptomycin sulphate, etc., are the chemicals used to isolate enzymes from cell free extract which has nucleic acids as the main contaminant along with lipids, simple sugar and so on.

5. ___________ is responsible for maintaining biologically native structure of an enzyme and even nucleic acid.
A. pH
B. Proton
C. ATP
D. Electrons
Answer: B
Clarification: Proton is responsible for maintaining biologically native structure of an enzyme and even nucleic acid. ATP required for performing metabolic activities is also a result of proton coupled to electron transport chain. Protons can be added or removed when change in pH occurs. Electrons have no role to play in maintaining structure of enzyme and nucleic acid.

6. Increase or decrease in _________ leads to protonation or deprotonation of bases which leads to melting of DNA in turn isolating the enzyme after centrifugation.
A. temperature
B. ionic strength
C. pH
D. detergent use
Answer: C
Clarification: Protons are responsible for maintain the biologically native structure of enzymes and nucleic acids. Hence increase or decrease in pH results in protonation or deprotonation of bases which leads to denaturation if DNA. The resultant extract in then centrifuged to isolate enzymes. The main limitation of this technique is the loss of enzymes due to denaturation.

7. The increase in pH affects the inter H₂ bonds and intramolecular hydrophobic bonds are majorly affected leading to denaturation of DNA.
A. True
B. False
Answer: B
Clarification: Increase or decrease in pH leads to protonation and deprotonation of bases which leads to denaturation of DNA. In this case, the inter H₂ bonds and intramolecular hydrophobic bonds are majorly affected to due to increase in temperature and not pH. This leads to denaturation of DNA and isolating the required enzyme. The main limitation in this case is denaturation of enzymes also, which can be prevented by optimizing the temperature and time parameters.

8. Cetyl trimethyl ammonium bromide is a cationic detergent.
A. True
B. False
Answer: A
Clarification: Cetyl trimethyl ammonium bromide is a cationic detergent because this positively charged detergent interacts electrostatically with negatively charged phosphodiester backbone of DNA. Followed by centrifugation, the precipitated DNA can be removed and enzymes can be isolated.

9. Which of the following chemical is not used to isolate enzymes from cell free extract?
A. Polyethyleneimine
B. Polyvinylpyrrolidone
C. EDTA
D. Magnesium chloride
Answer: C
Clarification: EDTA is a chelating agent which is used to chelate ions which are important for cell wall stability. Hence EDTA is a chemical method to extract enzymes from the cells. Whereas polyethyleneimine, polyvinylpyrrolidone, magnesium chloride etc., are used to isolate enzyme from cell free extract which contains nucleic acids as the major contaminant.

10. __________ is a compound which is frequently used for DNA removal.
A. 1.4% buffered sucrose
B. Protamine sulphate
C. Sodium hydroxide
D. Lysozyme
Answer: B
Clarification: Protamine sulphate is a compound which is frequently used for DNA removal, inturn isolating the enzyme of interest. 1.4% buffered sucrose is used for osmotic shock which is a chemical method for extracting the enzyme from cells. Sodium hydroxide is used in the alkali treatment which brings about nucleophilic attack and releasing the cell contents. Lysozyme is used to extract enzymes from gram positive bacteria as they have high content of peptidoglycan. As lysozyme catalyzes β(1 → 4) glycosidic linkage between NAG and NAM present in bacterial peptidoglycan.

11. Which of the following is the best method for isolating enzymes from cell free extract?
A. pH treatment
A. Temperature treatment
C. Chemical treatment
D. Osmotic shock
Answer: C
Clarification: Temperature and pH treatment have a major drawback of denaturing the enzyme itself. Hence the best treatment is chemical treatment as it has no major drawback. Osmotic shock is not a method for isolating enzyme, but extracting it. Hence it cannot be considered.