Question

Study the given replication fork and select the correct statement:

• A. Strands I and II have identical base sequences
• B. Strands I and III will be covalently bonded to each other after the completion of replication process
• C. Strand II and IV have antiparallel orientation
• D. Strands III and IV will get hydrogen bonded to each other after the completion of replication process

Answer 1

The correct option is C Strand II and IV have antiparallel orientation

In this figure, III and IV are the two strands of the parental DNA which got separated after the action of helicase. Hence, strand III and IV have antiparallel orientation.
Now, strand IV is the leading strand template with 3’ → 5’ polarity and strand II is complementary to strand IV. Strand III is the lagging strand template with 5’ → 3’ polarity and strand I is complementary to strand III. Since strand III and IV are complementary to each other, hence, their complementary stands, that is I and II are also complementary to each other.
Therefore, strand I and II are complementary to each other rather than being identical to each other.
Since, DNA replication is semi-conservative in nature, hence, each of the newly synthesized DNA molecules will have one parental strand and one daughter strand. Hence, strand I and III will pair with each other while strand II and IV will pair with each other, both by hydrogen bonding. Covalent bonds are not formed between the adjacent nitrogenous bases of two antiparallel strands in a double helical DNA.