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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >>
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Drift
See genetic drift.
Drosophila melanogaster
Fruit fly used as a model organism to study genetics, development and molecular biology.
Drug See Therapeutic agent.
Drug delivery
A technique by which a therapeutic agent is delivered to its site of action.
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For traditional therapeutic agents, this is synonymous with formulation. Biotechnology has made possible the development of a range of new therapeutic agent delivery systems, such as liposomes and other encapsulation techniques, as well as a variety of mechanisms that are capable of targeting a therapeutic agent to a particular cell or tissue. See therapeutic agent.
Drug development pathway
The pathway a new drug candidate goes through before it is accepted for human use. This involves preclinical research, which encompasses animal testing and formal testing for toxicology and ADME. This is followed by phase I trial in which the drug candidate is administered to 10-100 normal, healthy volunteers to establish pharmacokinetics.
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This requires compliance with GLP and registration for an investigational new drug application. In phase II trials, the drug is tried on a small number of hospital patients. Cancer drugs that are toxic to normal cells skip phase I and move directly to phase II trials. These trials are also known as ‘proof of efficacy’. Phase III trials are double blind and require hundreds or thousands of patients in about six hospital centres. Following phase III trials, the drug is submitted for approval, which may take few months to several years. Post marketing surveillance for adverse effects constitutes phase IV trials.
Drug discovery
The path of drug discovery involves discovering a target, discover a chemical that interferes with the target by structure-based drug design or a combination of high-throughput screening and combinatorial chemistry, followed by development of the drug by a series of regulated tests. See drug development pathway.
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Drug-induced hypoglycaemia
The most common cause of hypoglycaemia. In patients with diabetes mellitus, hypoglycaemia can occur due to insulin overdosage. Sulphonylureas, salicylates and antihistamines and overdoses of paracetamol can also cause hypoglycaemia.
Drug-resistance marker
A gene on a plasmid or other cloning vectors that produces an enzymes that degrades or detoxifies a drug. For example, the ampicillin-resistance marker encodes the enzyme β-lactamase that hydrolyses the antibiotic ampicillin. Bacteria containing the plasmid can be selected by growing in ampicillin-containing medium. Bacteria that do not contain the plasmid do not produce b-lactamase and are killed by ampicillin.
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Dry beriberi
See beriberi
Dry ice Solid carbon dioxide used as a cooling agent. Unlike water, dry ice sublimes changing directly into gas, making it an effective coolant.
Dry weight
The weight of a sample of biological material that has been dried to remove water.
Ds
Double-stranded (DNA or RNA).
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DscDNA See double-stranded complementary DNA.
DsDNA Double-stranded DNA.
DsRNA binding domain (dsRBD) A short module containing ~65 amino acid residues found in several proteins that bind dsRNA. Examples of some proteins containing this module include adenosine deaminase, dsRNA-dependent kinase, and E.coli RNaseIII. This motif contains 3 β strands, which form a sheet and 2 a-helices with the topology α-β-β-β-α. The binding interactions are believed to occur at a cleft in the domain between the second α-helix and the β-sheet.
Drug discovery cycle The cycle of events essential in the development of a new drug. Typically this involves research, preclinical testing and clinical development, and can take from 5 to 12 years.
Drug-induced hepatitis
Hepatitis induced by drugs such as isoniazid, halothane, phenytoin and methyldopa cause an idiosyncratic typ of hepatitis. The occurrence of hepatitis is infrequent, unpredictable and not dose-related. The morphological picture may resemble viral hepatitis or cholestasis.
Dual culture
A culture consisting of a plant tissue and another organism (such as a nematode) or an obligate parasite/microorganism (such as a fungus). This technique is used for a variety of purposes, including assessment of host-parasite interactions and the production of axenic cultures.
Dual energy X-ray absorptiometry (DEXA)
An instrument that uses the energy from very small doses of X-rays t determine bone mineral density (BMD) and to diagnose and follow the treatment of osteoporosis.
Dubin-johnson syndrome
One of the familial conjugated hyperbilirubinaemias that causes regurgitation jaundice. It is a benign autosomal recessive condition in which the conjugation of bilirubin is normal. However, there is a defect in the hepatic secretion of conjugated bilirubin is normal. However, there is a defet in the hepatic secretion of conjugated bilirubin into the bile. Secretion of other conjugated substances such as oestrogens and bromsulphthalein is also affected. There is accumulation of a brown pigment with staining properties of lipofuscin. The patients also show abnormal coproporphyrin excretion; the urine contains predominantly coproporphyrin I. Features of cholestasis are usually absent and plasma ALP activity is not elevated.
Duchenne muscular dystrophy An X-linked muscle wasting disease that is caused due to defects in the gene for the protein dystrophin. It predominantly affects males.
Dumb
A dumb terminal is a desktop display device that is incapable of local processing and does not support windowing applications (eg. VT52). The processing is carried out by the central computer.
Duplex
Synonymous with double helix.
Duplex DNA
Double-stranded DNA.
Duplication
The occurrence of a DNA sequence more than once in the same chromosome or genome.
DUST
A programme that filters low complexity regions from nucleic acid sequences.
Dyad
Two units or a pair.
Dyad symmetry
Property of a structure that can be rotated by 180º to produce the same structure.
Dye ligand chromatography
A special form of affinity chromatography in which a number of triazine dyes that contain both conjugated rings and ionic groups bind to some proteins enhancing their ability to bind to materials such as Sepharose.
Dynamic programming
A procedure for the comparison and alignment of strings or sequences in a manner that allows the computationally efficient incorporation of gaps.
Dynamic tests
Tests that assess function under stress. These are useful in detecting the site as well as the extent of the abnormality. For example, injection of adrenocorticotrophic hormone (ACTH) and measurement of plasma cortisol concentration can assess adrenal cortical function. The ability of the renal tubules to acidify urine can be tested by administering a large dose of ammonium chloride.
Dynamin
Cytosolic GTPase which binds to the neck of a clathrin-coated vesicle during budding from the membrane. It is involved in the completion of vesicle formation.
Dynein
A member of a family of motor proteins that move along microtubules by an ATP-dependent mechanism.
Dysfunction
Impaired function of an organ or body part.
Dysgammaglobulinaemias
A condition in which there is a defect in one or two immunoglobulins. Primary deficiency of lgA is the commonest of these with an incidence of 1 in 400. Although generally free from serious clinical symptoms, it may be associated with gastrointestinal, respiratory or renal infection.
Dyskinesia
Impaired control of voluntary movement that may result as a side effect of long-term use of antipsychotic medications.
Dysphagia
Difficulty in swallowing.
Dysplasia
Abnormal size, shape an organisation of adult cells.
Dystrophin
A large protein that links the cytoskeleton to the muscle membrane. Defects in the protein cause muscular dystrophy.
Dystrophy
1. Any degenerative disorder resulting from defective nutrition. 2. Abnormal development, degeneration of muscle, weakening.
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