Question

The segments of lagging stand are known as

• A. Cis element
• B. Klenow fragment
• C. Okazaki fragment
• D. Operon

Hint:

Replication is "semi-discontinuous" because the leading strand is continuous and the lagging strand is discontinuous (made of Okazaki fragments).
Remember: DNA Ligase is the "glue" that seals the gaps between these fragments.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question identifies a specific structural feature of DNA replication, focusing on the discontinuous synthesis that occurs on one of the two template strands.
Detailed Explanation:

• Leading vs. Lagging Strand:
DNA polymerase can only synthesize DNA in the $5' \rightarrow 3'$ direction.
At the replication fork, one template is oriented $3' \rightarrow 5'$, allowing continuous synthesis (Leading strand).
The other template is oriented $5' \rightarrow 3'$. To synthesize $5' \rightarrow 3'$, the polymerase must work away from the fork in short bursts.

• Okazaki Fragments:
These short, newly synthesized DNA segments formed on the lagging template strand are called Okazaki fragments, named after Reiji and Tsuneko Okazaki who discovered them in 1966.
Each fragment starts with an RNA primer and is eventually joined together by DNA ligase to form a continuous strand.

• Analyzing other options:
Cis element: A region of DNA that regulates the expression of genes located on the same chromosome (e.g., promoters, enhancers).
Klenow fragment: A large protein fragment produced when DNA polymerase I from E. coli is enzymatically cleaved; it retains polymerization and $3' \rightarrow 5'$ exonuclease activity but loses $5' \rightarrow 3'$ exonuclease activity.
Operon: A functioning unit of DNA containing a cluster of genes under the control of a single promoter.

Step 2: Final Answer:
The discontinuous segments synthesized on the lagging strand are known as Okazaki fragments.