Alright, let's analyze each of the given statements about Okazaki fragments in E. coli to determine which one is true.
1. They are sealed together by the action of helicase.
- Helicase is the enzyme responsible for unwinding the DNA double helix ahead of the replication fork, not joining fragments together. Okazaki fragments are joined by DNA ligase after being synthesized.
2. They are synthesized in the 3' to 5' direction.
- DNA synthesis occurs in the 5' to 3' direction for both the leading and lagging strands. It is not possible for DNA to be synthesized in the 3' to 5' direction due to the nature of the nucleotides and the enzymes involved in DNA replication.
3. They are usually 50 to 30 bases long.
- This statement is incorrect. In E. coli, Okazaki fragments are typically around 1000-2000 nucleotides long, significantly longer than the length mentioned.
4. They are formed on the lagging strand of DNA.
- This statement is correct. During DNA replication, the lagging strand is synthesized discontinuously in small segments known as Okazaki fragments.
Therefore, the correct statement about Okazaki fragments in E. coli is:
They are formed on the lagging strand of DNA.
