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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Dormancy Down Promoter Mutation
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Dopamine
A monoamine neurotransmitter synthesised from the amino acid tyrosine, involved in clinical syndromes such as schizophrenia. Dopamine deficiency is known to be responsible for Parkinson’s disease.
Dopamine b-hydroxylase
A Cu2+ containing mixed function oxidase that requires ascorbate as a cofactor and converts dopamine to norepinephrine within the chromaffin granules.
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DOS
Disk Operating system. A lower-level operating system that is used to read and copy files and carry out other basic functions. MS-DOS developed by Microsoft is integrated with Windows GUI.
Dosage compensation
Mechanisms that are used to compensate for the discrepancy between the presence of two X chromosomes in females but only one X chromosome in males. This is achieved by inactivation of one of the X chromosomes in female mammals, which results in males and females producing the same quantity of peptide from X-linked genes.
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Dosage mapping
Analysis of cell lines or somatic cell hybrids with multiple copies of a given chromosome. This allows genes to be mapped t the over-represented chromosome due to dosage detected by quantitative PCR, hybridisation or expression of product.
Dosimetry
The technique used to measure the dose and dose rate of radiation to which biological samples are exposed.
Dot(slot)blot
A hybridisation technique in which the target nucleic acids are applied directly to a nitrocellulose or nylon membrane in the form of dots or slots for hybridisation.
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Dot matrix
A graphical method for comparing two sequence with one sequence written horizontally across the top of the graph and the other along the left hand side. Dots are placed within the graph at the intersection of the same letter appearing in both the sequences. A series of diagonal lines in the graph indicate regions of alignment. The matrix can be filtered to reveal regions of similarity by scoring a minimal threshold number of matches within a sequence window.
Double blind
A study in which neither the investigators administering the treatment nor the participants know which participants are receiving the experimental treatment and which are receiving the placebo.
Double crossover
Two reciprocal breakage and reunion events that occur simultaneously between two DNA molecules.
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Double digestion
The digestion of DNA with two restriction enzymes. This is useful in mapping DNA and in cloning DNA fragments into a vector in a particular orientation.
Double helix A structure in which two polynucleotide strands are helically twisted and stabilized by hydrogen bonding and base stacking.
Double immunodiffusion
An immunological technique in which both antigen and antibody diffuse radially from wells towards each other.
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As equivalence is reached, a visible line of precipitation forms. This is an effective quantitative tool for determining the relationship between antigens and the presence of a number of antigen-antibody systems.
Double minutes
Small fragments of a chromosome containing many copies of a particular gene. methotrexate exposure causes amplification of the dihydrofolate reductase (DHFR) gene manifest either as homogeneously staining regions of the chromosome or in the form of extrachromosomal double minutes.
Dormancy
(F.dormir, from L. dormire, to sleep) An inactive period in the life of an animal or plant during which growth slows or completely stops. Physiological changes that are associated with dormancy enable the organism to survive adverse environmental conditions. While annual plants survive the winter as dormant seeds, many perennial plant survive as dormant tubers, rhizomes, or bulbs. In animals, hibernation and aestivation enable them to survive extremes of cold and heat, respectively.
Dorsal
Refers to the back of an animal, or the upper surface of a leaf, wing, etc.
Dorsoventral
Refers to the axis that runs from the back to the abdomen of an animal or from the upperside to the underside of a structure.
Double negative T cell
An immature T cell that expresses neither CD4 nor CD8 on its membrane.
Double positive T cell
An immature T cell which express both CD4 and CD8 its membrane.
Double recessive
An organism homozygous for a recessive allele at each of two loci.
Double-reciprocal plot
Rearrangement of the Michaelis-Menten equation by taking reciprocals on both sides and plotting 1/v0 against 1/[S] gives a straight line and a slope of km/Vmax. This is useful in the determination of Vmax and Km for an enzyme. See Lineweaver-Burk plot.
Double-stranded complementary DNA (dscDNA)
A double-stranded DNA molecule generated from a cDNA template.
Double thymidine block
A technique used to synchronise cells in culture. When high concentration of thymidine is added to the culture, it blocks DNA replication. As a result, all treated cells proceed through their cell cycle and stop at the same point.
Doubling time
See Generation time.
Down
The state of a computer when it is non-operational and not available for use.
Down syndrome
A genetic disease characterised by inheritance of three copies (trisomy) of chromosome 21. Patients with this syndrome are mentally retarded and exhibit several phenotypic abnormalities such as broad skull, short stature, folding of skin around the eye (epicanthal fold), stubby hands and feet.
Download
The transfer of files from a computer network or internet onto a local computer.
Downmutations
Mutations in the promoter sequence that decrease the frequency of transcription initiation.
Down-promoter mutation
A change in the sequence of a gene promoter that results in decreased expression of that gene.
Downstream
1. In molecular biology, the DNA sequence that lies in the 3’ direction of the transcription start site, which is designated as +1. Downstream sequences are marked with plus signs, eg. +2, +3, etc. Also denotes the 3’ side of a particular DNA sequence or gene. 2. In chemical engineering, indicates those phases of a manufacturing process that follow the biotransformation stage. Refers the recovery and purification of the product of fermentation. Also termed downstream processing.
Downstream processing
See downstream 2.
Doxorubicin (adriamycin)
An anthracycline antibiotic with a planar tetracyclic ring that intercalates into DNA leading to DNA unwinding and strand breaks. It is used as a cancer chemotherapeutic agent.
DR antigen
MHC class II molecules found on B cells and antigen-presenting cells of humans.
Draft sequence
The sequence generated by the HGP in June 2000 in the form of 10,000 base pair-sized fragments whose approximate chromosomal locations are known. Although the draft sequence is incomplete, it provided a road map to 95% of human genes. See finished DNA sequence.
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