This set of Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Microbial Metabolism – Biosynthesis of Deoxyribonucleic Acid”.
1. In DNA molecule, the amount of purines is equal to the amount of pyrimidines.
Explanation: In DNA the nitrogenous bases like adenine binds with thymine, and guanine binds with cytosine. As a consequence, the ratio of adenine to thymine or of guanine to cytosine in double stranded DNA is always 1:1. So the amount of purines is equal to the amount of pyrimidines.
2. RNA consists of which combination of bases?
a) Thymine, Guanine, Cytosine
b) Guanine, Cytosine, Uracil
c) Thymine, Adenine, Guanine
d) Adenine, Cytosine, Thymine
Explanation: RNA is composed of nitrogenous bases adenine, guanine, cytosine and uracil. They do not contain thymine as present in DNA.
3. Which of the following are features of semiconservative replication?
a) RNA replicates DNA molecule
b) The DNA molecule produced contains two old templates
c) One new DNA helix is formed
d) DNA duplicates itself and the new chain contains old template strand and new complementary strand
Explanation: In semiconservative replication DNA duplication occurs in which one polynucleotide chain acts as a template to direct the synthesis of a new chain complementary to itself. It results in two daughter helices, each containing one old template strand and one new complementary strand.
4. The chromosome of a typical bacterium is ________________
a) circular double-stranded DNA
b) circular single-stranded DNA
c) double-helix DNA
d) single stranded DNA
Explanation: The chromosome of a typical bacterium is a circular double-stranded DNA molecule; that is, the double helix for a complete genome has no free ends.
5. If the chromosome were extended linearly then it would approximately measure?
a) 13500 micrometre
b) 1000 micrometre
c) 1250 micrometre
d) 500 micrometre
Explanation: If the chromosome were extended linearly then it would measure approximately 1250 micrometers or 1.25 mm which is several hundred times longer than the bacterial cell that contains it.
6. The Lambda Bacteriophage carries out which of the following replication methods?
a) Theta mode
b) Sigma mode
c) Linear mode
d) Does not carry out replication
Explanation: The Lambda Bacteriophage follows sigma mode of replication in which the intermediate structures of DNA have sigma conformation. In this replication begins with the cleavage of a phosphodiester bond in one strand of the circular DNA molecule to produce a nick with 3’-OH and 5’-PO4 ends on that strand.
7. Which of the following replication methods leads to the production of two circular daughter chromosomes?
a) Theta mode
b) Sigma mode
c) Linear mode
d) Rolling circle method
Explanation: In Theta mode of replication a circular parental chromosome is replicated to two circular daughter chromosomes, in each of which one strand of the parental DNA molecule is conserved and a complementary strand is newly synthesized.
8. Eukaryotes replicate their DNA from one origin or growing point per molecule.
Explanation: Procaryotes replicate their DNA from one origin or growing point per molecule while eukaryotes replicate from many origins per molecule. Replication may occur in either a unidirectional or bidirectional manner from each origin.
9. DNA gyrase is a ______________ protein.
Explanation: DNA gyrase is a helix-relaxing protein which works along with other enzymes and participates in opening the parental DNA helix ahead of the replication fork.
10. Which of the following enzyme removes the RNA primer with its 5’-nuclease activity?
a) DNA polymerase I
b) DNA polymerase II
c) DNA polymerase III
d) RNA polymerase
Explanation: DNA polymerase I remove the RNA primer with its 5”-nuclease activity; simultaneously it fills in the gap with DNA via its 3’-polymerase activity.
Sanfoundry Global Education & Learning Series – Microbiology.
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