biology : class12 DNA Precipitation : DNA Isolation, Restriction Enzymes, Vector, Ligation, Host Cell : Recombinant DNA Technology MCQ Questions and Answers
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DNA Precipitation
MCQ questions and answers.
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MCQ Questions
1. Which alcohol is commonly used to precipitate DNA from an aqueous solution?
A.
Ethanol
B.
Methanol
C.
Formaldehyde
D.
Acetic acid
Correct Answer:
Ethanol
Explanation:
Ethanol reduces DNA solubility in the presence of salt, causing the DNA to precipitate from the aqueous solution.
2. Why is salt added during DNA precipitation?
A.
To neutralize the negative charges on DNA
B.
To digest DNA into smaller fragments
C.
To increase DNA replication
D.
To stain the DNA blue
Correct Answer:
To neutralize the negative charges on DNA
Explanation:
Salt provides positive ions that help neutralize the negatively charged phosphate groups of DNA, allowing DNA molecules to aggregate and precipitate.
3. Which temperature condition generally improves DNA precipitation using ethanol?
A.
Chilled ethanol
B.
Boiling ethanol
C.
Room-temperature water
D.
Warm saline solution
Correct Answer:
Chilled ethanol
Explanation:
Cold ethanol lowers DNA solubility and helps DNA precipitate more efficiently.
4. What is usually observed after centrifuging a DNA precipitation mixture?
A.
A DNA pellet
B.
A protein crystal
C.
A lipid layer
D.
A gas bubble
Correct Answer:
A DNA pellet
Explanation:
Centrifugation collects the precipitated DNA at the bottom of the tube as a pellet.
5. Which alcohol can also be used instead of ethanol for DNA precipitation?
A.
Isopropanol
B.
Glycerol
C.
Benzene
D.
Acetone
Correct Answer:
Isopropanol
Explanation:
Isopropanol is commonly used to precipitate DNA from an aqueous solution, usually in the presence of salt.
6. What is commonly used to wash a DNA pellet after precipitation?
A.
70% ethanol
B.
Concentrated acid
C.
Boiling water
D.
Detergent solution
Correct Answer:
70% ethanol
Explanation:
A 70% ethanol wash removes residual salts and other impurities while keeping the DNA precipitated.
7. After DNA precipitation and washing, what is usually done with the DNA pellet?
A.
It is dissolved in a suitable buffer
B.
It is burned to release DNA
C.
It is mixed with concentrated acid
D.
It is boiled until it evaporates
Correct Answer:
It is dissolved in a suitable buffer
Explanation:
The purified DNA pellet is redissolved in a suitable buffer or water for further use.
8. What is the main purpose of adding ethanol during DNA isolation?
A.
To make DNA insoluble so it can be collected
B.
To copy the DNA molecule
C.
To cut DNA at specific sites
D.
To join DNA fragments together
Correct Answer:
To make DNA insoluble so it can be collected
Explanation:
Ethanol decreases the solubility of DNA, causing it to precipitate and become collectable by centrifugation.
9. Which part of the DNA molecule is mainly affected by salt during precipitation?
A.
The negatively charged phosphate backbone
B.
The nitrogen bases only
C.
The deoxyribose sugars only
D.
The hydrogen atoms of water
Correct Answer:
The negatively charged phosphate backbone
Explanation:
Salt ions interact with the negatively charged phosphate groups in the DNA backbone and help DNA molecules aggregate during precipitation.
10. What happens to DNA when sufficient chilled alcohol and salt are added to an aqueous DNA solution?
A.
DNA precipitates out of the solution
B.
DNA changes into protein
C.
DNA is cut into nucleotides
D.
DNA becomes permanently gaseous
Correct Answer:
DNA precipitates out of the solution
Explanation:
Chilled alcohol and salt reduce DNA solubility, causing the DNA to come out of the aqueous solution as a precipitate.
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