lagging strand elongation

Definition

Target type: biologicalprocess

The process in which an existing DNA strand is extended in a net 3' to 5' direction by activities including the addition of nucleotides to the 3' end of the strand, complementary to an existing template, as part of DNA replication. Lagging strand DNA elongation proceeds by discontinuous synthesis of short stretches of DNA, known as Okazaki fragments, from RNA primers; these fragments are then joined by DNA ligase. Although each segment of nascent DNA is synthesized in the 5' to 3' direction, the overall direction of lagging strand synthesis is 3' to 5', mirroring the progress of the replication fork. [GOC:mah, ISBN:071673706X, ISBN:0815316194]

Lagging strand elongation is a fundamental process in DNA replication, ensuring the complete copying of the entire genome. It involves the synthesis of a new DNA strand in a discontinuous manner, opposite to the leading strand. Here's a detailed breakdown:

1. **DNA Unwinding:** The DNA double helix is unwound by helicase, separating the two strands and creating a replication fork.

2. **Primer Synthesis:** RNA primase initiates lagging strand synthesis by synthesizing a short RNA primer, which provides a 3'-OH group for DNA polymerase to bind to.

3. **Okazaki Fragment Synthesis:** DNA polymerase III, with its 5' to 3' polymerase activity, elongates the RNA primer, adding new nucleotides complementary to the template strand. This results in short, discontinuous fragments of newly synthesized DNA known as Okazaki fragments.

4. **Primer Removal and Replacement:** Once an Okazaki fragment is complete, RNase H removes the RNA primer, leaving a gap. DNA polymerase I, possessing both 5' to 3' polymerase and 5' to 3' exonuclease activity, fills the gap by replacing the RNA primer with DNA nucleotides.

5. **Joining Okazaki Fragments:** DNA ligase catalyzes the formation of a phosphodiester bond between the 3'-OH end of one Okazaki fragment and the 5'-phosphate end of the adjacent fragment, linking them together to create a continuous lagging strand.

6. **Continuous Process:** As the replication fork progresses, this entire process repeats, with new RNA primers being laid down upstream, creating new Okazaki fragments, which are then processed, ligated, and added to the growing lagging strand.

Lagging strand elongation is a complex and coordinated process, involving the precise actions of multiple enzymes and proteins to ensure accurate and complete DNA replication.'
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Proteins (2)

Compounds (11)