Describe the process of DNA replication and the functions of the enzymes involved
DNA helicase unwinds the DNA strand. DNA polymerase adds a nucleic acid to the original strand of DNA. DNA ligase seals the gap between Okazaki fragments on lagging strand to create one continuous DNA strand.
DNA replication is the process by which a cell makes an exact copy of its DNA before cell division. The process involves three main steps: initiation, elongation, and termination.
1. Initiation: The process of DNA replication begins when an enzyme called helicase unwinds the double helix structure of the DNA molecule. This creates a replication fork, which is a Y-shaped structure in the DNA. At the replication fork, two strands of DNA are separated from each other, and the replication process begins.
2. Elongation: The next step of DNA replication is elongation. In this step, an enzyme called DNA polymerase binds to the single-stranded DNA at the replication fork. DNA polymerase reads the nucleotide sequence of the template strand and begins to build a new complementary strand of DNA. The new strand is built in the 5′ to 3′ direction, meaning that DNA polymerase can only add new nucleotides to the 3′ end of the newly synthesized strand. The other strand, called the lagging strand, is synthesized in the 3′ to 5′ direction and in short segments called Okazaki fragments.
3. Termination: The final step of DNA replication is termination. When the replication fork reaches the end of the DNA molecule, the newly synthesized strands are separated and the replication process comes to an end. Two identical copies of the original DNA molecule have been made.
There are several enzymes involved in the process of DNA replication, each with specific functions:
1. Helicase: An enzyme that unwinds the double helix of the DNA molecule to create a replication fork.
2. DNA polymerase: An enzyme that synthesizes a new strand of DNA by attaching nucleotides together in a specific order, using the existing DNA strand as a template.
3. Primase: An enzyme that synthesizes a short RNA primer that DNA polymerase uses as a starting point to add nucleotides to the growing strand of DNA.
4. Ligase: An enzyme that seals the gaps between Okazaki fragments by joining the sugar-phosphate backbone of adjacent DNA segments.
5. Topoisomerase: An enzyme that relieves the tension caused by the unwinding of the DNA double helix during replication.
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