DNA replication

Overview of the process of DNA replication in cells

DNA replication

DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. This process occurs in all living organisms and is the basis for biological inheritance. DNA is made up of a double helix of two complementary strands. During replication, these strands are separated. Each strand of the original DNA molecule then serves as a template for the production of its counterpart, a process referred to as semiconservative replication.

Overview

DNA replication begins at specific locations in the genome, called "origins". The unwinding of DNA at the origin, and synthesis of new strands, forms a replication fork. The process is initiated by the binding of a group of proteins to the origin, including helicase, which unwinds the DNA, and primase, which synthesizes a short RNA primer. DNA polymerases then extend the DNA strand from the RNA primer.

Initiation

The initiation of DNA replication involves the recognition of the origin of replication by initiator proteins. In prokaryotes, this is often a single origin, while in eukaryotes, there are multiple origins of replication. The initiator proteins recruit other proteins to form the pre-replication complex.

Elongation

During elongation, the enzyme DNA polymerase synthesizes a new DNA strand by adding nucleotides complementary to the template strand. DNA polymerase can only add nucleotides to the 3' end of a DNA strand, so replication proceeds in the 5' to 3' direction. The leading strand is synthesized continuously, while the lagging strand is synthesized in short segments called Okazaki fragments.

Termination

Termination of DNA replication occurs when two replication forks meet, or when the replication machinery reaches the end of a linear chromosome. In eukaryotes, the ends of linear chromosomes are protected by telomeres, which are extended by the enzyme telomerase.

Enzymes involved

Several key enzymes are involved in DNA replication:

• Helicase – unwinds the DNA double helix.
• Primase – synthesizes RNA primers.
• DNA polymerase – synthesizes new DNA strands.
• Ligase – joins Okazaki fragments on the lagging strand.
• Topoisomerase – relieves the tension caused by unwinding of DNA.

Errors and proofreading

DNA replication is a highly accurate process, but errors can occur. DNA polymerases have proofreading abilities that allow them to correct mistakes by removing incorrectly paired nucleotides. Additional repair mechanisms, such as mismatch repair, further increase the fidelity of DNA replication.

Significance

DNA replication is essential for cell division, allowing genetic information to be passed from one generation to the next. Errors in replication can lead to mutations, which may result in genetic disorders or contribute to the development of cancer.

Also see

• Central dogma of molecular biology
• Transcription (biology)
• Translation (biology)
• Genetic recombination
• DNA repair

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