Depiction of the adenine–thymine Watson–Crick base pair
c:o6-methyl-guanine pair in the polymerase-2 basepair position
DNA polymerase moves along the old strand in the 3'–5' direction, creating a new strand having a 5'–3' direction.
crystal structure of rb69 gp43 in complex with dna containing thymine glycol
DNA polymerase with proofreading ability
3D structure of the DNA-binding helix-turn-helix motifs in human DNA polymerase beta (based on PDB file 7ICG)
phi29 dna polymerase, orthorhombic crystal form, ssdna complex

The regular structure and data redundancy provided by the DNA double helix make DNA well suited to the storage of genetic information, while base-pairing between DNA and incoming nucleotides provides the mechanism through which DNA polymerase replicates DNA and RNA polymerase transcribes DNA into RNA.

- Base pair

Before replication can take place, an enzyme called helicase unwinds the DNA molecule from its tightly woven form, in the process breaking the hydrogen bonds between the nucleotide bases.

- DNA polymerase
Depiction of the adenine–thymine Watson–Crick base pair

5 related topics

Alpha

The structure of the DNA double helix. The atoms in the structure are colour-coded by element and the detailed structures of two base pairs are shown in the bottom right.

DNA

Polymer composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.

Polymer composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses.

The structure of the DNA double helix. The atoms in the structure are colour-coded by element and the detailed structures of two base pairs are shown in the bottom right.
Chemical structure of DNA; hydrogen bonds shown as dotted lines. Each end of the double helix has an exposed 5' phosphate on one strand and an exposed 3' hydroxyl group (—OH) on the other.
A section of DNA. The bases lie horizontally between the two spiraling strands ([[:File:DNA orbit animated.gif|animated version]]).
DNA major and minor grooves. The latter is a binding site for the Hoechst stain dye 33258.
From left to right, the structures of A, B and Z DNA
DNA quadruplex formed by telomere repeats. The looped conformation of the DNA backbone is very different from the typical DNA helix. The green spheres in the center represent potassium ions.
A covalent adduct between a metabolically activated form of benzo[a]pyrene, the major mutagen in tobacco smoke, and DNA
Location of eukaryote nuclear DNA within the chromosomes
T7 RNA polymerase (blue) producing an mRNA (green) from a DNA template (orange)
DNA replication: The double helix is unwound by a helicase and topo­iso­merase. Next, one DNA polymerase produces the leading strand copy. Another DNA polymerase binds to the lagging strand. This enzyme makes discontinuous segments (called Okazaki fragments) before DNA ligase joins them together.
Interaction of DNA (in orange) with histones (in blue). These proteins' basic amino acids bind to the acidic phosphate groups on DNA.
The lambda repressor helix-turn-helix transcription factor bound to its DNA target
The restriction enzyme EcoRV (green) in a complex with its substrate DNA
Recombination involves the breaking and rejoining of two chromosomes (M and F) to produce two rearranged chromosomes (C1 and C2).
The DNA structure at left (schematic shown) will self-assemble into the structure visualized by atomic force microscopy at right. DNA nanotechnology is the field that seeks to design nanoscale structures using the molecular recognition properties of DNA molecules.
Maclyn McCarty (left) shakes hands with Francis Crick and James Watson, co-originators of the double-helix model.
Pencil sketch of the DNA double helix by Francis Crick in 1953
A blue plaque outside The Eagle pub commemorating Crick and Watson

The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules (A with T and C with G), with hydrogen bonds to make double-stranded DNA.

Here, the two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase.

Human chromosomes (grey) capped by telomeres (white)

Telomere

Region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes.

Region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes.

Human chromosomes (grey) capped by telomeres (white)
Lagging strand during DNA replication.
Shelterin co-ordinates the T-loop formation of telomeres.
Synthesis of chromosome ends by telomerase
The average cell will divide between 50 and 70 times before cell death. As the cell divides the telomeres on the end of the chromosome get smaller. The Hayflick limit is the theoretical limit to the number of times a cell may divide until the telomere becomes so short that division is inhibited and the cell enters senescence.

During DNA-replication, DNA polymerase cannot replicate the sequences present at the 3'-ends.

It has since been questioned whether the last lagging strand primer is placed exactly at the 3'-end of the template and it was demonstrated that it is rather synthesized at a distance of about 70-100 nucleotides which is consistent with the finding that DNA in cultured human cell is shortened by 50-100 base pairs per cell division.

DNA damage resulting in multiple broken chromosomes

DNA repair

Collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome.

Collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome.

DNA damage resulting in multiple broken chromosomes
Structure of the base-excision repair enzyme uracil-DNA glycosylase excising a hydrolytically-produced uracil residue from DNA. The uracil residue is shown in yellow.
Double-strand break repair pathway models
DNA ligase, shown above repairing chromosomal damage, is an enzyme that joins broken nucleotides together by catalyzing the formation of an internucleotide ester bond between the phosphate backbone and the deoxyribose nucleotides.
DNA repair rate is an important determinant of cell pathology
Most life span influencing genes affect the rate of DNA damage
A chart of common DNA damaging agents, examples of lesions they cause in DNA, and pathways used to repair these lesions. Also shown are many of the genes in these pathways, an indication of which genes are epigenetically regulated to have reduced (or increased) expression in various cancers. It also shows genes in the error-prone microhomology-mediated end joining pathway with increased expression in various cancers.

It involves switching out regular DNA polymerases for specialized translesion polymerases (i.e. DNA polymerase IV or V, from the Y Polymerase family), often with larger active sites that can facilitate the insertion of bases opposite damaged nucleotides.

Pol η is known to add the first adenine across the T^T photodimer using Watson-Crick base pairing and the second adenine will be added in its syn conformation using Hoogsteen base pairing.

DNA replication: The double helix is un'zipped' and unwound, then each separated strand (turquoise) acts as a template for replicating a new partner strand (green). Nucleotides (bases) are matched to synthesize the new partner strands into two new double helices.

DNA replication

Biological process of producing two identical replicas of DNA from one original DNA molecule.

Biological process of producing two identical replicas of DNA from one original DNA molecule.

DNA replication: The double helix is un'zipped' and unwound, then each separated strand (turquoise) acts as a template for replicating a new partner strand (green). Nucleotides (bases) are matched to synthesize the new partner strands into two new double helices.
DNA polymerases adds nucleotides to the 3′ end of a strand of DNA. If a mismatch is accidentally incorporated, the polymerase is inhibited from further extension. Proofreading removes the mismatched nucleotide and extension continues.
Overview of the steps in DNA replication
Steps in DNA synthesis
Role of initiators for initiation of DNA replication.
Formation of pre-replication complex.
Scheme of the replication fork.
a: template, b: leading strand, c: lagging strand, d: replication fork, e: primer, f: Okazaki fragments
Many enzymes are involved in the DNA replication fork.
The assembled human DNA clamp, a trimer of the protein PCNA.
E. coli Replisome. Notably, the DNA on lagging strand forms a loop. The exact structure of replisome is not well understood.
The cell cycle of eukaryotic cells.
Dam methylates adenine of GATC sites after replication.
Replication fork restarts by homologous recombination following replication stress
Epigenetic consequences of nucleosome reassembly defects at stalled replication forks

Most prominently, DNA polymerase synthesizes the new strands by adding nucleotides that complement each (template) strand.

Nucleobases are matched between strands through hydrogen bonds to form base pairs.

Gregor Mendel

Gene

Basic unit of heredity and a sequence of nucleotides in DNA that encodes the synthesis of a gene product, either RNA or protein.

Basic unit of heredity and a sequence of nucleotides in DNA that encodes the synthesis of a gene product, either RNA or protein.

Gregor Mendel
Fluorescent microscopy image of a human female karyotype, showing 23 pairs of chromosomes. The DNA is stained red, with regions rich in housekeeping genes further stained in green. The largest chromosomes are around 10 times the size of the smallest.
Schematic of a single-stranded RNA molecule illustrating a series of three-base codons. Each three-nucleotide codon corresponds to an amino acid when translated to protein
Protein coding genes are transcribed to an mRNA intermediate, then translated to a functional protein. RNA-coding genes are transcribed to a functional non-coding RNA.
Inheritance of a gene that has two different alleles (blue and white). The gene is located on an autosomal chromosome. The white allele is recessive to the blue allele. The probability of each outcome in the children's generation is one quarter, or 25 percent.
A sequence alignment, produced by ClustalO, of mammalian histone proteins
Evolutionary fate of duplicate genes.
Depiction of numbers of genes for representative plants (green), vertebrates (blue), invertebrates (orange), fungi (yellow), bacteria (purple), and viruses (grey). An inset on the right shows the smaller genomes expanded 100-fold area-wise.
Gene functions in the minimal genome of the synthetic organism, Syn 3.
Comparison of conventional plant breeding with transgenic and cisgenic genetic modification.

Two chains of DNA twist around each other to form a DNA double helix with the phosphate-sugar backbone spiraling around the outside, and the bases pointing inwards with adenine base pairing to thymine and guanine to cytosine.

The copies are made by specialized enzymes known as DNA polymerases, which "reads" one strand of the double-helical DNA, known as the template strand, and synthesize a new complementary strand.