Base pair

Depiction of the adenine–thymine Watson–Crick base pair

Fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds.

- Base pair
Depiction of the adenine–thymine Watson–Crick base pair

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Alpha

Base pairing: Two base pairs are produced by four nucleotide monomers, nucleobases are in blue. Guanine (G) is paired with cytosine (C) via three hydrogen bonds, in red. Adenine (A) is paired with uracil (U) via two hydrogen bonds, in red.

Thymine

One of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T.

One of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T.

Base pairing: Two base pairs are produced by four nucleotide monomers, nucleobases are in blue. Guanine (G) is paired with cytosine (C) via three hydrogen bonds, in red. Adenine (A) is paired with uracil (U) via two hydrogen bonds, in red.

The mutations caused by thymine deficiency appear to occur only at AT base pair sites in DNA and are often AT to GC transition mutations.

Chemical structure of uridine

Uracil

One of the four nucleobases in the nucleic acid RNA that are represented by the letters A, G, C and U. The others are adenine (A), cytosine (C), and guanine (G).

One of the four nucleobases in the nucleic acid RNA that are represented by the letters A, G, C and U. The others are adenine (A), cytosine (C), and guanine (G).

Chemical structure of uridine

In RNA, uracil base-pairs with adenine and replaces thymine during DNA transcription.

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.

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.

Match up between two DNA bases (guanine and cytosine) showing hydrogen bonds (dashed lines) holding them together

Complementarity (molecular biology)

Related to Molecular biology.

Related to Molecular biology.

Match up between two DNA bases (guanine and cytosine) showing hydrogen bonds (dashed lines) holding them together
Match up between two DNA bases (adenine and thymine) showing hydrogen bonds (dashed lines) holding them together
Complementarity between two antiparallel strands of DNA. The top strand goes from the left to the right and the lower strand goes from the right to the left lining them up.
Left: the nucleotide base pairs that can form in double-stranded DNA. Between A and T there are two hydrogen bonds, while there are three between C and G. Right: two complementary strands of DNA.
A sequence of RNA that has internal complementarity which results in it folding into a hairpin
A sequence of RNA showing hairpins (far right and far upper left), and internal loops (lower left structure)
Formation and function of miRNAs in a cell

The degree of complementarity between two nucleic acid strands may vary, from complete complementarity (each nucleotide is across from its opposite) to no complementarity (each nucleotide is not across from its opposite) and determines the stability of the sequences to be together.

A strip of eight PCR tubes, each containing a 100 μL reaction mixture

Polymerase chain reaction

Method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) to a large enough amount to study in detail.

Method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) to a large enough amount to study in detail.

A strip of eight PCR tubes, each containing a 100 μL reaction mixture
Placing a strip of eight PCR tubes into a thermal cycler
A thermal cycler for PCR
An older, three-temperature thermal cycler for PCR
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Ethidium bromide-stained PCR products after gel electrophoresis. Two sets of primers were used to amplify a target sequence from three different tissue samples. No amplification is present in sample #1; DNA bands in sample #2 and #3 indicate successful amplification of the target sequence. The gel also shows a positive control, and a DNA ladder containing DNA fragments of defined length for sizing the bands in the experimental PCRs.
Tucker PCR
Exponential amplification
Diagrammatic representation of an example primer pair. The use of primers in an in vitro assay to allow DNA synthesis was a major innovation that allowed the development of PCR.
"Baby Blue", a 1986 prototype machine for doing PCR

Most PCR methods amplify DNA fragments of between 0.1 and 10 kilo base pairs (kbp) in length, although some techniques allow for amplification of fragments up to 40 kbp.

Graphical representation of the idealized human diploid karyotype, showing the organization of the genome into chromosomes. This drawing shows both the male (XY) and female (XX) versions of the 23rd chromosome pair. Chromosomes are shown aligned at their centromeres. The mitochondrial DNA is not shown.

Human genome

Complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria.

Complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria.

Graphical representation of the idealized human diploid karyotype, showing the organization of the genome into chromosomes. This drawing shows both the male (XY) and female (XX) versions of the 23rd chromosome pair. Chromosomes are shown aligned at their centromeres. The mitochondrial DNA is not shown.
Number of genes (orange) and base pairs (green, in millions) on each chromosome.
Human genes categorized by function of the transcribed proteins, given both as number of encoding genes and percentage of all genes.
TSC SNP distribution along the long arm of chromosome 22 (from https://web.archive.org/web/20130903043223/http://snp.cshl.org/ ). Each column represents a 1 Mb interval; the approximate cytogenetic position is given on the x-axis. Clear peaks and troughs of SNP density can be seen, possibly reflecting different rates of mutation, recombination and selection.
Populations with a high level of parental-relatedness result in a larger number of homozygous gene knockouts as compared to outbred populations.
A pedigree displaying a first-cousin mating (carriers both carrying heterozygous knockouts mating as marked by double line) leading to offspring possessing a homozygous gene knockout.

Haploid human genomes, which are contained in germ cells (the egg and sperm gamete cells created in the meiosis phase of sexual reproduction before fertilization) consist of 3,054,815,472 DNA base pairs (if X chromosome is used), while female diploid genomes (found in somatic cells) have twice the DNA content.

The interaction of tRNA and mRNA in protein synthesis.

Transfer RNA

Adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino acid sequence of proteins.

Adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino acid sequence of proteins.

The interaction of tRNA and mRNA in protein synthesis.
Secondary cloverleaf structure of tRNAPhe from yeast.
Tertiary structure of tRNA. CCA tail in yellow, Acceptor stem in purple, Variable loop in orange, D arm in red, Anticodon arm in blue with Anticodon in black, T arm in green.
3D animated GIF showing the structure of phenylalanine-tRNA from yeast (PDB ID 1ehz). White lines indicate base pairing by hydrogen bonds. In the orientation shown, the acceptor stem is on top and the anticodon on the bottom
Bulge-helix-bulge motif of a tRNA intron

The anticodon forms three complementary base pairs with a codon in mRNA during protein biosynthesis.

Simplified diagram of mRNA synthesis and processing. Enzymes not shown.

Transcription (biology)

Process of copying a segment of DNA into RNA.

Process of copying a segment of DNA into RNA.

Simplified diagram of mRNA synthesis and processing. Enzymes not shown.
Regulation of transcription in mammals. An active enhancer regulatory region of DNA is enabled to interact with the promoter DNA region of its target gene by formation of a chromosome loop. This can initiate messenger RNA (mRNA) synthesis by RNA polymerase II (RNAP II) bound to the promoter at the transcription start site of the gene.  The loop is stabilized by one architectural protein anchored to the enhancer and one anchored to the promoter and these proteins are joined to form a dimer (red zigzags).  Specific regulatory transcription factors bind to DNA sequence motifs on the enhancer.  General transcription factors bind to the promoter.  When a transcription factor is activated by a signal (here indicated as phosphorylation shown by a small red star on a transcription factor on the enhancer) the enhancer is activated and can now activate its target promoter.  The active enhancer is transcribed on each strand of DNA in opposite directions by bound RNAP IIs.  Mediator (a complex consisting of about 26 proteins in an interacting structure) communicates regulatory signals from the enhancer DNA-bound transcription factors to the promoter.
This shows where the methyl group is added when 5-methylcytosine is formed
Simple diagram of transcription elongation
Image showing RNA polymerase interacting with different factors and DNA during transcription, especially CTD (C Terminal Domain)
The Image shows how CTD is carrying protein for further changes in the RNA
Electron micrograph of transcription of ribosomal RNA. The forming ribosomal RNA strands are visible as branches from the main DNA strand.
Scheme of reverse transcription

Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language.

c:o6-methyl-guanine pair in the polymerase-2 basepair position

DNA polymerase

Member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA.

Member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA.

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

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.

Chemical structure of RNA

Nucleic acid sequence

Succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA or RNA (GACU) molecule.

Succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA or RNA (GACU) molecule.

Chemical structure of RNA
A series of codons in part of a mRNA molecule. Each codon consists of three nucleotides, usually representing a single amino acid.
A depiction of the genetic code, by which the information contained in nucleic acids are translated into amino acid sequences in proteins.
Electropherogram printout from automated sequencer for determining part of a DNA sequence
Genetic sequence in digital format.

The nucleobases are important in base pairing of strands to form higher-level secondary and tertiary structure such as the famed double helix.