Okazaki Fragments - Discovery, Formation, and Functions

Okazaki Fragments Definition: Cell division is a complex biological process involving the replication of a cell's genetic information stored in long DNA strands. This replication is facilitated by enzymes called DNA polymerases. Each DNA strand is a template for DNA polymerases to create a complementary strand. During this process, one strand at the replication fork is continuously synthesized in the 5′ to 3′ direction (known as the leading strand).

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What are Okazaki Fragments?

1. Elimination of the RNA primers using either RNase H or Pol I.
2. Filling of the gaps with DNA through the action of Pol I.
3. Connection of the ends through DNA ligase.

Fatty Acid Biosynthesis

Okazaki Fragments Discovery

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Formation of Okazaki Fragments

Racemose Inflorescence

Why Okazaki Fragments are Formed?

Okazaki Fragments Functions

1. DNA Replication Process: DNA replication is the process by which a cell makes an identical copy of its DNA. This process is essential for cell division and ensures that each new cell receives a complete set of genetic information.
2. Replication Fork Formation: DNA replication occurs at a structure called the replication fork, which is formed when the double-stranded DNA molecule is unwound by enzymes called DNA helicases. The unwinding of the DNA molecule creates two single-stranded template strands.
3. DNA Polymerase Activity: Once the DNA molecule is unwound, DNA polymerases begin to synthesize new DNA strands using the single-stranded template strands. DNA polymerases can only add nucleotides to the growing DNA strand in the 5' to 3' direction.
4. Leading and Lagging Strand: During DNA replication, two new DNA strands are synthesized: the leading strand and the lagging strand. The leading strand is synthesized continuously in the 5' to 3' direction, following the movement of the replication fork. However, the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments.
5. Okazaki Fragment Synthesis: The discontinuous synthesis of the lagging strand is due to the orientation of the template strand. The template strand for the lagging strand is oriented in the 3' to 5' direction, which is opposite to the direction of DNA synthesis.
6. DNA Polymerase Action on Lagging Strand: To overcome this orientation problem, DNA polymerase synthesizes short fragments of DNA in the 5' to 3' direction away from the replication fork. These short DNA fragments are known as Okazaki fragments.
7. Joining of Okazaki Fragments: After an Okazaki fragment is synthesized, an enzyme called DNA ligase joins the fragment to the previously synthesized Okazaki fragment. This process continues until the entire lagging strand is synthesized.
8. Completion of Lagging Strand: Once all the Okazaki fragments have joined, another enzyme called DNA polymerase I removes the RNA primers from the Okazaki fragments and replaces them with DNA nucleotides. This ensures that the final lagging strand is a complete and continuous molecule of DNA.

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Okazaki Fragments Significance