How DNA copies itself — practice questions

Question 1 · difficulty L1 · recall

Which enzyme unwinds the DNA double helix at the replication fork?

• A. Ligase
• B. Helicase
• C. DNA polymerase
• D. Primase

Question 2 · difficulty L2 · understanding

The direction in which DNA polymerase synthesises a new strand:

• A. 3 prime to 5 prime
• B. 5 prime to 3 prime
• C. without a template
• D. both directions on one strand simultaneously

Question 3 · difficulty L2 · understanding

The mode of DNA replication demonstrated by Meselson and Stahl:

• A. non-templated
• B. semiconservative
• C. conservative only
• D. dispersive only

Question 4 · difficulty L3 · application

Why is DNA synthesis on one template strand discontinuous?

• A. The replication fork moves in both directions on the same strand
• B. The template strand contains no bases
• C. Ligase blocks continuous synthesis
• D. DNA polymerase synthesises only in the 5′ to 3′ direction

Question 5 · difficulty L3 · understanding

In a chromosome, there is a specific DNA sequence, responsible for initiating replication. It is called as:

• A. Recognition sequence
• B. Cloning site
• C. Restriction site
• D. ori site

Question 6 · difficulty L3 · understanding

Which of the following statement is correct regarding the process of replication in E.coli?

• A. 'The DNA dependent DNA polymerase catalyses polymerization in one direction that is $$3^{\prime} \rightarrow 5$$'
• B. The DNA dependent RNA polymerase catalyses polymerization in one direction, that is $$5^{\prime} \rightarrow 3^{\prime}$$
• C. The DNA dependent DNA polymerase catalyses polymerization in 5' $$\rightarrow$$ 3' as well as $$3^{\prime} \rightarrow 5^{\prime}$$ direction
• D. The DNA dependent DNA polymerase catalyses polymerization in 5' $$\rightarrow$$ 3' direction

Question 7 · difficulty L3 · understanding

Given below are two statements Statement I : DNA polymerases catalyse polymerisation only in one direction, that is 5' → 3'. Statement II : During replication of DNA, on one strand the replication is continuous while on other strand it is discontinuous. In the light of the above statements, choose the correct answer from the options given below:

• A. Statement I is incorrect but Statement II is correct
• B. Both Statement I and Statement II are correct
• C. Both Statement I and Statement II are incorrect
• D. Statement I is correct but Statement II is incorrect

Question 8 · difficulty L3 · understanding

The process of translation of mRNA to proteins begins as soon as:

• A. The small subunit of ribosome encounters mRNA
• B. The larger subunit of ribosome encounters mRNA
• C. Both the subunits join together to bind with mRNA
• D. The tRNA is activated and the larger subunit of ribosome encounters mRNA

Question 9 · difficulty L3 · understanding

Ten E.coli cells with 15 N - dsDNA are incubated in medium containing 14 N nucleotide. After 60 minutes, how many E.coli cells will have DNA totally free from 15 N?

• A. 20 cells
• B. 40 cells
• C. 60 cells
• D. 80 cells

Question 10 · difficulty L4 · analysis

A mutation disables DNA ligase during replication. Which defect is most directly expected?

• A. Okazaki fragments remain unjoined
• B. The parental strands cannot unwind
• C. RNA primers cannot form
• D. Complementary bases cannot pair