Detergent
A substance that lowers the surface tension of a solution, thereby improving its cleaning properties (e.g. Twee-20^TM, a surfactant and wetting agent). See surfactant; wetting agent. A detergent contains both hydrophilic and hydro phobic parts and is capable of dissolving lipids.

Determinant
That part of the antigen molecule which nobinds to an antibody-combining site or to a receptor on T cells.

Determination
The process by which undifferentiated cells in an embryo become committed to develop into specific cell types, such as neutrons, or muscle cells.

Dextranase
An enzyme that catalyses the breakdown of dextran

Dextrin
A molecule made up of a number of glucose residues that results from hydrolysis of starch by α- amylase.

Dextrorotatory isomer
A stereoisomer that rotates the plane of polarized light clockwise.

Dextrose
See glucose

dG.dC tailing
See complementary homopolymeric tailing.

Diabetes insipidus
A disease characterised by the excretion of large of volume of urine (polyuria) and compensatory excessive water intake (polydipsia) in response to thrist. Plasma osmolality and the concentration of sodium are increased, whereas the urine is dilute. In mild cases, urine volume is about 2.5-6 L/d, whereas in severe cases, 16-24 L/d may be avoided. The increase in plasma osmolality stimulates thrist. Normally, when water is available, dehydration does not occur, but if water intake is inadequate, there is severe dehydration with weakness, fever, mental disturbances, prostration and death. Diabetes insipidus may be due to pituitary or hypothalamic disease (central diabetes insipidus) or to failure of the kidneys to respond to vasopressin(nephrogenic diabetes insipidus)

Diabetes mellitus
A metabolic syndrome arising due to insulin deficiency and characterised by high blood glucose levels (fasting venous plasma glucose concentration greater  than 7.8mmol/L (140mg/dL) and greater than equal 11.1 mmol/L (greater than equal 200 mg/dl) 2h after a carbohydrate meal or 2h after oral ingestion of 75g of glucose (WHO).

Diabetes mellitus, type 1 (formerly insulin-dependent diabetes mellitus (IDDM), juvenile-onset diabetes). Diabetes mellitus that usually presents in childhood and adolescence. However, about 25 per cent  of the cases may occur at any age. The patients are liable to develop ketoacidosis. The disease is suggested to be inherited as a multigenic trait.
A genetic predisposition followed by an environmental insult (viral infection) causes an inflammatory response in the pancrease termed “insulitis”. This results in transformation of the β cell surface from “self” to “non-self” leading to activation of the immune system and destruction of β cells. The HLA DQb1* 0302 is recognised as a susceptibility gene associated gene associated with high risk for diabetes, while the HLA D b1* 0602, is reported to be a dominant protective allele.

Diabetes mellitus, type 2 (formerly non-insulin-dependent diabetes mellitus (NIDDM), adult-onset diabetes). Diabetes mellitus that results due to insulin resistance, relative insulin deficiency or from a secretory defect. Although patients with type 2 are usually over 40 years, the disease may also occur in young people. Patients with type 2 are not prone to diabetic ketoacidosis. The interaction of multiple genetic and environmental factors is believed to produce the diabetic phenotype. Approximately 40 per cent of patients with type 2 are obese. High risk factors include diet, life-style and stress.