DNA replication

In the lab we can amplify (replicate many copies) of specific genes using PCR, or clone many segments of DNA using bacteria. However, this overview will demonstrate how DNA is replicated in a cell.

DNA replication begins with a double helix of DNA.

DNA helicase

Formation of a replication fork: A protein called Helicase breaks the hydrogen bonds of the two strands of DNA forming a replication fork.

Binding proteins

Stabilization of a replication fork: Binding proteins keep the two DNA strands apart, preserving the replication fork.

Primase

Primase forms RNA Primers: The enzyme primase makes a short segment of RNA called the RNA Primer on the DNA termed the template DNA.

Polymerase

Formation of new DNA Strands: An enzyme called DNA polymerase adds DNA nucleotides (individual A, G, T, C) to the RNA primer on the template DNA.

Continuation of DNA synthesis: DNA strand synthesis continues in a 5' to 3' direction with the new strand termed the nascent strand.

Proofreading checks DNA bases: DNA polymerase proceeds along the nascent leading strand continuously, proofreading DNA nucleotides and replacing incorrect DNA bases

Formation of continous DNA: RNA primers are removed by proteins, and a protein called Ligase fuses the sugar-phosphate backbone of the nascent lagging DNA strand

Bidirectional synthesis

Replication proceeds in two local directions

Okazaki fragments form: DNA polymerase procedes along the nascent leading strand continuously. Okazaki fragments form in about 150 bp stretches along the nascent lagging strand, fused together by ligase.

Summary of DNA Replication

A protein called Helicase breaks the Hydrogen Bonds of the two strands of DNA forming a Replication Fork.

Proteins called Binding Proteins keep the two DNA strands apart preserving the Replication Fork.

A protein called Primase makes a short segment of RNA called the RNA Primer on the DNA termed the Template DNA.

A protein called DNA Polymerase adds DNA Nucleotides to the RNA Primer on the Template DNA.

DNA Polymerase Proofreads DNA Nucleotides and replaces incorrect DNA bases.

DNA Strand Synthesis continues in a 5' to 3' direction with the new strand termed the Nascent Strand.

Okazaki Fragments form in about150 DNA base stretches along the 5' to 3' Template DNA.

RNA Primers are removed by Proteins and a protein called Ligase fuses Sugar-phosphate Backbone of the Nascent DNA Strand.

Mitosis and Meiosis

Somatic cells (non-reproductive cells) contain a characteristic number of chromosomes. For mitosis to occur, during the S-phase of a cell's lifecycle duplicates the chromosomes to create sister chromatids.

mtDNA Replication