Question

Okazaki fragments are synthesized on
A. Leading strands of DNA only
B. Lagging strands of DNA only
C. Both leading and lagging strands of DNA
D. Complementary DNA

Answer 1

Hint: DNA replication results in the formation of two types of new strands namely the continuous strands and the discontinuous short strands called okazaki fragments. Okazaki fragments are brief, non-continuous sequences of DNA nucleotides that occur during DNA replication. These fragments are linked together by the enzyme DNA ligase after being discontinuously produced. In eukaryotes, the Okazaki fragments range in size from \[150\] to \[200\] bp.

Complete answer:
Option:B – Okazaki fragments are synthesized as the lagging strands of DNA.
Okazaki fragments are small, newly synthesized discontinuous DNA fragments that are formed during DNA replication on the template strand with the polarity \[5'\] to\[3'\]. They create small double-stranded DNA portions which later on combined with the help of replication enzymes. This is because DNA polymerase can extend the growing DNA strand at \[3'\] end.

So, Option:B is the correct answer.

Additional information:
Option:A – DNA synthesis on leading strand having the polarity \[3'\] to \[5'\] end is continuous as the DNA polymerase synthesizes an antiparallel complementary strand in the direction \[5'\] to \[3'\]. Hence, the Okazaki fragments are not synthesized on the leading strand.
So, Option:A is not correct.
Option:C – DNA synthesis is continuous on the leading strand and is discontinuous on the lagging strand. So, Okazaki fragments are not synthesized on both the strands.
So, Option:C is not correct.
Option:D – Complementary DNA is produced in a reverse transcription process.
So, Option:D is not correct.

Note:
Since the two chromosomal DNA strands are antiparallel, one (leading strand) is mainly duplicated in a continuous way, while the other (lagging strand) is produced in short portions known as Okazaki fragments. This difference occurs because the major DNA synthesizing enzyme, the DNA Polymerase can only add nucleotides to the \[3'\] end of growing new complementary DNA strands.