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What is DNA Replication Simplified

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Understanding the Basics of DNA Replication

DNA replication is a biological process that occurs in all living organisms and copies their DNA

 

DNA Replication Begins at an Origin of Replication

An origin of replication is a site within a chromosome that serves as a starting point for DNA replication.

At the origin, the two DNA strands unwind, and DNA replication proceeds outward from the origin in opposite directions, a process termed bidirectional replication.

Bidirectional replication starts at the origin of replication and proceeds until the new stands meet each other on the opposite side of the chromosome.

DNA replication. The double helix is unwound and each strand acts as a template for the next strand. Bases are matched to synthesize the new partner strands.
DNA replication. The double helix is unwound and each strand acts as a template for the next strand. Bases are matched to synthesize the new partner strands.

 

Replication Forks

An origin of replication provides an opening called a replication bubble that forms two DNA replication forks.

DNA replication occurs near the opening that forms each replication fork.

The synthesis of a strand always begins with a primer and the new DNA is made in the 5′ to 3′ direction.

The DNA replication fork. RNA primer labeled at top.
The DNA replication fork. RNA primer labeled at top.
  1. A primer is a strand of nucleic acid that serves as a starting point for DNA synthesis.
  2. They are required for DNA replication because the enzymes that catalyze this process, DNA polymerases, can only add new nucleotides to an existing strand of DNA.
  3. The polymerase starts replication at the 3′-end of the primer, and copies the opposite strand.

 

One strand, called the leading strand, is made in the same direction that the fork is moving.

The leading strand is synthesized as one long continuous molecule.

The other daughter strand, the lagging strand, is made as a series of small fragments that are eventually connected to each other to form a continuous strand.

The synthesis of these fragments occurs in the direction away from the fork.

 

Proteins Involved in DNA Replication

 

Protein Name

Protein Function

DNA Helicase

Separates double-stranded DNA into single strands

Single-Strand
Binding Protein

Binds to single-stranded DNA, and prevents it from re-forming a double helix

Topoisomerase

Removes tightened coils ahead of the replication fork

DNA Primase

Synthesizes short RNA Primers

DNA Polymerase

Synthesizes DNA in the leading and lagging strands, removes RNA primers, and fills in gaps

DNA Ligase

Covalently attaches adjacent Okazaki Fragments

 

 

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