Question

What is incorrect about the above figure representing DNA replication?

• A. The direction of DNA replication in strand (i)
• B. The direction of DNA replication in strand (ii)
• C. Discontinuous replication of strand (i)
• D. Discontinuous replication of strand (ii)

Answer 1

Answer: (C)

DNA polymerase can polymerize nucleotides only in $5^{\prime }\to 3^{\prime }$ direction on $3^{\prime }\to 5^{\prime }$ strand because it adds them at the $3^{\prime }$ end. Since, the two strands of DNA run in antiparallel directions, the two templates provide different ends for replication. Replication over the two templates thus proceeds in opposite directions. One strand with polarity $3^{\prime }\to 5^{\prime }$ forms its complementary strands continuously because $3^{\prime }$ end of the latter is open for elongation. It is called leading strand. Replication is discontinuous on the other template with polarity $5^{\prime }\to 3^{\prime }$ because only a short segment of DNA strand can be built in $5^{\prime }\to 3^{\prime }$ direction due to exposure of a small stretch of template at one time. Short segments of replicated DNA are called Okazaki fragments.