Microbiology MCQ – MCQ questions on DNA Replication

MN Editors

| Last Update:

1. DNA replication is

  • Semi-conservative, continuous, unidirectional
  • Conservative, continuous
  • Semi-conservative, semi-discontinuous
  • Semi-Continuous, conservative

[expand title=”Show Answer”]Answer is C. DNA is semi Conservative and semi discontinues.
Semiconservative replication would produce two copies that each contained one of the original strands and one new strand. Conservative replication would leave the two original template DNA strands together in a double helix and would produce a copy composed of two new strands containing all of the new DNA base pairs.

When the double helix of DNA unwinds, DNA replication on one of the two strands (3′ to 5′ stand) can easily proceed continuously in 5′ to 3′ direction.


2. During replication of DNA

  • The two daughter molecules develop from both the parental strands
  • RNA functions as template
  • One strand from parent and one strand freshly formed in the two daughter molecules
  • One daughter receives both the parental strands while the other daughter receives newly formed strands

[expand title=”Show Answer”]Answer is C. One strand from parent and one strand freshly formed in the two daughter molecules

3. When DNA replication starts

  • The leading strand produces Okazaki fragments.
  • The hydrogen bonds between the nucleotides of two strands break.
  • The phosphodiester bonds between the adjacent nucleotides break.
  • The bonds between the nitrogen base and deoxyribose sugar break.

[expand title=”Show Answer”]Correct option is B)
Okazaki fragments are produced on lagging strand. DNA replication starts with unwinding of DNA duplexes which are held together by hydrogen bond. Helicases move along the double stranded DNA and separate the strands by breaking hydrogen bonds between base pairs. ATP hydrolysis provides the required energy for breaking of hydrogen bonds. DNA polymerase enzyme adds deoxyribonucleotides to primer by formation of phosphodiester bond betweenbetween the 3′ oxygen of a growing strand and alpha phosphate of a dNTP. Breaking of bond between nitrogen base and deoxyribose sugar is part of nucleotide catabolism; it does not occurs during DNA replication. Thus, the correct answer is option B.

4. In bacterial DNA replication, synthesis starting from the site of origin of replication

  • Involves RNA primers
  • Requires telomerase
  • Proceeds unidirectionally
  • Moves bidirectionally

[expand title=”Show Answer”]Correct option is D)
DNA replication is bidirectional mechanism because two replication forks are formed at the origin which moves in opposite directions, with both template strands being copied at each fork. Thus, the correct answer is option D.

5. Gap between division phase and start of DNA-replication is called?

  • G1 – Phase
  • G2- Phase
  • M – Phase

[expand title=”Show Answer”]Correct option is A)


6. Replication of DNA is in

  • 3′- 5’direction
  • 5′- 3′ direction

[expand title=”Show Answer”]DNA replication occurs in 5’to 3′ direction whereas the parent or template DNA is read in 3’to 5′ DNA. Normal DNA polymerases are 5′-to-3′ polymerases. DNA polymerases extend the 3′ tail of the DNA molecule but it synthesises 5′-to-3′. 3′ to 5′ polymerases would never work because the energy required would be way too high. When DNA is replicating, there are two strands necessary to do this. One is called a template strand which serves as the strand who’s complementary strand will be synthesised. The other is called primer strand which will be extended in the direction of synthesis. When polymerization occurs, the DNA polymerase attaches to the 3′ -OH of the pentose sugar of the previous nucleotide of the primer strand. Unless it finds that -OH, synthesis is halted.
So, the correct answer is option B.

Submit Your Question
Please submit your question in appropriate category.
Most Searched Posts