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glossary:dna

DNA

deoxyribonucleic acid

(1) DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.

(2)Acronym for deoxyribonucleic acid, usually 2'-deoxy-5'-ribonucleic acid. DNA is a code used within cells to form proteins.

The molecule that encodes genetic information in the nucleus of cells. It determines the structure, function and behaviour of the cell.

dna is a double-stranded molecule held together by weak hydrogen bonds between base pairs of nucleotides. The four nucleotides in dna contain the bases: adenine (a), guanine (g), cytosine ©, and thymine (t).

in nature, base pairs form only between a and t and between g and c, thus the base sequence of each single strand can be deduced from that of its partner. (biochemistry) a long linear polymer found in the nucleus of a cell and formed from nucleotides and shaped like a double helix; associated with the transmission of genetic information; DNA is the king of molecules.An acronym for one of the nucleic acids, standing for deoxyribonucleic acid. dna contains all the genetic information required to create an organism of a species. One cell also contains all this genetic information which is capable of being cloned to produce an exact copy of its parent. The dna material in an organism provides the information that is passed on to offspring.

Chromosomal DNA

In animal cells, a structure in the nucleus, containing a linear thread of deoxyribonucleic acid (DNA), which transmits genetic information and is associated with ribonucleic acid and histones.

Circular DNA

A DNA molecule that is a closed-ring structure, found in mitochondria, prokaryote chromosomes, plasmids, and certain viruses.

Closed DNA complexes

The first of two kinetically distinct steps required for RNA polymerase to initiate transcription in which the RNA polymerase holoenzyme binds electrostatically to the promoter DNA.

Complementary DNA (cDNA)

Copy DNA DNA transcribed from a specific RNA through the action of the enzyme reverse transcriptase.

Copy DNA

A DNA copy of mRNA which contains only regulatory and coding sequences, i.e. introns have been removed. mRNA is copied into double-stranded DNA using reverse transcriptase; the cDNA can then be cloned and amplified and introduced into an expression vector (plasmid or phage) and its protein product produced in either bacterial, yeast, insect or mammalian cells. Called also cDNA.

DNA binding proteins

Are of two general types, histone proteins which are part of the unit structure of chromosomes called nucleosomes and nonhistone proteins which are present in small amounts and include regulatory proteins.

DNA construct

A DNA molecule which has been inserted into a cloning vector.

DNA glycosylases

Enzymes involved in the excision-repair mechanisms for DNA.

DNA gyrase

One of the type II topoisomerases involved in the supercoiling of double-stranded circular DNA molecules.

DNA library

A collection of cloned DNA molecules from a genome.

DNA ligase

An enzyme that seals nicks in the DNA helix, joins Okazaki fragments together during DNA replication and is essential in recombinant DNA technology for DNA cloning.

DNA microarray

An ordered set of thousands of different oligonucleotides immobilized on a microscope slide or other solid surface used for the detection of cognate nucleotide sequences such as the pattern of gene expression in a particular cell population by hybridization with fluorescently labeled cDNA prepared from total mRNA isolated from the cells.

DNA polymerase

Of Escherichia coli; has three distinct enzymatic activities: (a) a 5' to 3' polymerase activity which, under the direction of a template DNA, catalyzes the addition of mononucleotide units, produced from deoxynucleoside 5'-triphosphates, to the 3'-hydroxyl terminus of a primer chain; (b) a 5' to 3' exonuclease active only on duplex DNA; © a 3' to 5' exonuclease primarily active on single-stranded DNA which can selectively remove mismatched terminal nucleotides, thus carrying out a proofreading function. Additionally it catalyzes both the pyrophosphorolysis of DNA, a reaction which is the reverse of polymerization, and pyrophosphate exchange which represents a repetitive sequence of nucleotide addition and pyrophosphorolysis.

DNA repair

A series of enzymatic mechanisms whereby errors or damage to one of the two DNA strands are removed by excision and replaced by correct nucleotides using the undamaged strand as template. The mechanisms include removal of lesions of depurination and DNA glycosylases which recognize altered bases.

DNA sequencing

Determining the order of nucleotides in DNA from which amino acid in a polypeptide chain can be predicted.

DNA transcription

see deoxyribonucleic acid.

DNA translation

see deoxyribonucleic acid.

Duplex DNA

Double-stranded DNA.

End labeling DNA

Methods for labeling DNA with radioisotopes or other detectable marker molecules at the ends using the terminal transferase 3'-labeling or polynucleotide kinase for 5'-labeling.

Episomal DNA

That present in a cell as extra chromosomal; exemplified by plasmids of prokaryotic cells.

Eukaryotic DNA

See deoxyribonucleic acid.

Exogenous DNA

The DNA that has been introduced into a host by cloning.

Junk DNA

Noncoding regions of DNA that have no apparent function. The term “junk DNA” is a disparaging one, expressing some of the disappointment felt by geneticists when they first gazed upon sizable segments of the genetic code and, instead of seeing one wonderful gene after another, they saw a few exons surrounded by vast stretches of “junk DNA.”

Exons are the regions of DNA that contain the code for producing the polypeptide molecules that make up protein. Each exon codes for a specific portion of the complete protein. In humans and some other species, the exons are separated by long regions of junk DNA.

However, junk DNA has been found to be even more conserved than protein-coding regions of the DNA in humans and other mammalian species. The extent of conservation indicates that there is some function for junk DNA that remains to be determined. Junk DNA may prove not to be junk.

Mitochondrial DNA

Mitochondrial DNA (mtDNA) is the DNA of the mitochondrion, a structure situated in the cytoplasm of the cell rather than in the nucleus (where all the other chromosomes are located).

All mtDNA is inherited from the mother. There are 2 to 10 copies of the mtDNA genome in each mitochondrion.

mtDNA is a double-stranded, circular molecule. It is very small relative to the chromosomes in the nucleus and so contains only a limited number of genes. It is specialized in the information it carries and encodes a number of the subunits in the mitochondrial respiratory-chain complex that the cell needs to respire. (It also contains genes for some ribosomal RNAs and transfer RNAs).

Mutations (changes) in mtDNA can cause disease. The mutations often impair the function of oxidative-phosphorylation enzymes in the respiratory chain. This is especially manifest in tissues with a high energy expenditure such as brain and muscle.

Point mutations in mtDNA, for example, are associated with:

NARP – which stands for Neuropathy, Ataxia and Retinitis Pigmentosa: a disease with proximal muscle weakness, wobbliness, retinal disease, seizures and developmental delay; MELAS – which stands for Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke: a disease with migraine-like attacks of headache & vomiting, hemiplegia (weakness on one side of the body), visual defect, hearing loss, exercise intolerance and weakness, loss of consciousness, seizures, mental retardation or dementia, and elevated lactic acid in blood; MERRF – which stands for Myoclonic Epilepsy and Ragged Red Fibers: a disease with epilepsy, myoclonus (shock-like contraction of muscle), cerebellar dysfunction of the cerebellar portion of the brain, hearing loss and dementia; Leber's hereditary optic atrophy – the onset in midlife (average age 30) of painless central visual loss that progresses over a period averaging 4 months, affecting both eyes affected; and Leigh's syndrome – a disease starting usually in the 1st year of life with hypotonia (floppiness), episodes of vomiting, ataxia (wobbliness), choreoathetosis (abnormal involuntary writhing movements), hyperventilation, loss of motor and verbal milestones, spasticity, hearing loss, visual loss, carbohydrate intolerance, high lactic acid, and death often within 2 years of onset.

All mtDNA at fertilization comes from the oocyte. Therefore, inherited mtDNA mutations are transmitted from the mother to all offspring, male and female alike. The higher the level of mutant mtDNA in the mother's blood, the higher is the frequency of clinically affected offspring and the more severely the children tend to be affected.

Each cell in the body contains different mtDNA populations. Due to presence of multiple mitochondria in cells, each cell contains several mtDNA copies. This produces tissue variation so that a mutation in mtDNA vs normal mtDNA can vary widely among tissues in an individual.

There is thus a threshold effect. The percent of mutant mtDNAs must be above a certain threshold to produce clinical disease. This threshold varies from tissue to tissue because the percent of mutant mDNAs needed to cause cell dysfunction varies according to the oxidative requirements of the tissue, affecting particularly organs with a high energy needs such as brain and muscle.

Mobile DNA

A sequence present in the variable locations on the chromosome. Called also jumping genes.

Noncoding DNA

The strand of DNA that does not carry the information necessary to make proteins. DNA normally has two strands – the coding strand and the non-coding strand. Although these strands are exact mirror images of one another, only the coding strand contains the information for making proteins. The non-coding strand does not.

Noncoding DNA is also known as the antisense strand.

Nuclear DNA (nDNA)

The DNA of the chromosomes found in the nucleus of a eukaryotic cell.

Open DNA complex

A local opening of about 10 base pairs formed at the transcription initiation site following the electrostatic binding of RNA polymerase holoenzyme to the promoter region.

Recombinant DNA

A novel DNA sequence formed by the joining, usually in vitro, of two non-homologous DNA molecules.

DNA resulting from gene-splicing: DNA extracted from two or more different sources such as genes from different organisms and joined together to form a single molecule or fragment.

Redundant DNA

DNA made up of copies of the same or nearly the same nucleotide sequence. DNA sequences that are present in many copies per chromosome set. Repetitive DNA sequences may be closely linked (eg satellite DNA or VNTR loci) or dispersed throughout the genome or parts of the genome (eg alu family). SYN: repetitive DNA

Repeat DNA

repetitive DNA - includes (a) satellite DNA and so-called (b) interspersed repeated DNA sequences. The latter are interspread throughout the chromosomes in hundreds of thousands of individual copies, each about 300 nucleotides long; they are, unlike satellite DNA, transcribed.

Repetitive DNA

DNA made up of copies of the same or nearly the same nucleotide sequence. DNA sequences that are present in many copies per chromosome set. Repetitive DNA sequences may be closely linked (eg satellite DNA or VNTR loci) or dispersed throughout the genome or parts of the genome (eg alu family). SYN: redundant DNA

Satellite DNA

Short, highly repeated eukaryotic DNA sequences, usually clustered in heterochromatin and generally not transcribed. single copy DNA (scDNA) nucleotide sequences present once in the haploid genome, as are most of those encoding polypeptides in the eukaryotic genome.

Selfish DNA

A mobile DNA element that appears to have no function except to replicate itself. Part of junk DNA.

Single-copy DNA

The fraction of DNA that contains most of the protein-coding genes and reassociates most slowly.

Single-stranded DNA

Produced when double-stranded DNA is denatured or found naturally in some viruses.

Spacer DNA

The nucleotide sequences occurring between genes.

Supercoiled DNA

The double helix is itself twisted.

Superhelical DNA

A twisted structure formed by circular DNA molecules. See also supercoiled DNA (above).

Triple-Stranded DNA

A triple-stranded DNA is a structure of DNA in which three oligonucleotides wind around each other and form a triple helix. In this structure, one strand binds to a B-form DNA double helix through Hoogsteen or reversed Hoogsteen hydrogen bonds.

Unique DNA

DNA sequences that occur only once in the haploid genome.

Z-DNA

An alternative structural form of DNA which differs from the more commonly occurring B- and related A-form in that the helix is left handed compared with the right hand helixes of B- and A-forms. Z is for zig-zag. The functional significance of Z-DNA is unknown.

See: RNA

Sources: Biology OnLine; Dorland's Medical Dictionary for Health Consumers; Saunders Comprehensive Veterinary Dictionary; MedicineNet

glossary/dna.txt · Last modified: 2012/10/16 14:40 (external edit)