Question

Okazaki fragments are

• A. The DNA fragments produced due to radiation
• B. The RNA primers required for initiation of DNA synthesis
• C. Short DNA fragments on the lagging strand
• D. Short fragments on the leading strand

Answer 1

Answer: (C)

Short DNA fragments on the lagging strand

DNA synthesis always occurs in the 5'-->3' because chain growth results from the formation of a phosphodiester bond between the 3' oxygen of a growing strand and $\alpha$ phosphate of a dNTP. As we know that the two strands of the parental DNA duplex are antiparallel and DNA polymerases can add nucleotides to the growing new strands only in the 5'-->3' direction. The leading strand synthesis proceeds continuously from a single RNA primer in the 5'-->3' direction. To facilitate the growth of the lagging strand in the 5'-->3' direction, copying of its template strand must somehow occur in the opposite direction from the movement of the replication fork. This is done by synthesizing a new primer every few hundred bases on the second parental strand. Each of these primers is elongated in the 5'-->3' direction and form discontinuous segments called Okazaki fragments which are later joined together by DNA ligase. DNA polymerase can not initiate the DNA synthesis de novo and needs a small nucleotide fragment, called primer, to add deoxyribonucleotides to it. The DNA fragment produced due to radiation are called fragments only. Option C is the correct answer.