Base pair and Related Topics

Cytosine

One of the four nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA).

In Watson-Crick base pairing, it forms three hydrogen bonds with guanine.

Nucleic acid

Nucleic acids are biopolymers, macromolecules, essential to all known forms of life.

The Swiss scientist Friedrich Miescher discovered nucleic acid first naming it as nuclein, in 1868. Later, he raised the idea that it could be involved in heredity.

Using amino acids and the process known as protein synthesis, the specific sequencing in DNA of these nucleobase-pairs enables storing and transmitting coded instructions as genes.

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.

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.

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.

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.

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.

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.

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.

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

Complementarity (molecular biology)

Related to Molecular biology.

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.

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.

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

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

Thymine

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

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.

An energy pyramid illustrates how much energy is needed as it flows upward to support the next trophic level. Only about 10% of the energy transferred between each trophic level is converted to biomass.

Biomass (ecology)

Mass of living biological organisms in a given area or ecosystem at a given time.

Humans and their livestock represent 96% of all mammals on earth in terms of biomass, whereas all wild mammals represent only 4%.

Globally, terrestrial and oceanic habitats produce a similar amount of new biomass each year (56.4 billion tonnes C terrestrial and 48.5 billion tonnes C oceanic).

Grasses, trees and shrubs have a much higher biomass than the animals that consume them

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The total number of DNA base pairs on Earth, as a possible approximation of global biodiversity, is estimated at 5.3, and weighs 50 billion tonnes.

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.

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.