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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Anticoding Strand Antimetabolites

Antibody-directed enzyme prodrug therapy See ADEPT.
Antibody diversity The mechanism which generates a large number of (>108) different heave and light chain gene sequences and therefore antibody specificities. Site-specific recombination of VDJ sequences for the heavy chain, and VJ sequences for the light chain is responsible for antibody diversity.
Antiobody-mediated (humoral) immune response The synthesis of antibodies by B cells in response to a foreign immunogen.

Anticonvulsant A therapeutic agent that prevents seizures.
Antidepressant A drug used to prevent or treat depression. Antidepressant drugs include selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors, tricyclic antidepressants, tetracyclic antidepressants, and others.
Antidiuretic  A chemical substance that counteracts the effect of a diuretic.
Antidiuretic hormone (ADH) Also called vasopressin. A hormone synthesised in the hypothalamus, stored in the pituitary and secreted in response to an increase in ECF osmolality or hypovolaemia. ADH renders the renal collecting ducts permeable to water and enhances water reabsorption in excess of solute. This concentrates the urine and dilutes the ECF. ADH secretion is under the control of the hypothalamus, which responds to impulses from stretch receptors in the left atrium and baroreceptors in the aortic arch and carotid sinus.

Antigen (immunogen) A foreign substance that elicits an immune response by stimulating the formation of antibodies. The antigen, generally a protein, when introduced into an organism is bound by the antibody or a T cell receptor. See antigenic determinant; antigenic switching.
Antigen-binding site That part of an immunoglobulin molecule that binds antigen specifically.
Antigen processing The process that involves breakdown of large molecules within macrophages into presentation of peptides within the groove of MHC molecules.
Antigen processing/presenting cell A heterogeneous group of cells that bind antigens on their surface and interact with helper T cells. This process is required for T-cell activation. The dendritic cells in lymphoid Langerhan cells in the skin and some macrophages are examples of antigen-presenting cells.

Antigen receptor The specific antigen-binding receptor on T or B lymphocytes. The receptors arise from rearrangements of V genes.
Antigenic determinant (epitope) A surface feature of a microorganism or macromolecule that elicits an immune response.
Antigenic drift A mutation that causes a small change in antigen structure.

Antigenic shift A mutation that causes a large change in antigen structure.
Antigenic switching A change in the surface antigens of a microorganism by genetic, rearrangement, to elude detection by the host immune system.
Antigenic variation The ability of certain pathogenic microorganisms to change the antigens on the cell surface as a mechanism to evade attack by the immune system.
Antihaemophilic globulin (factor VIII) A clotting factor that reduces the clotting time of blood. Factor VIII is absent in individuals with classic haemophilia (haemoiphilia A) inherited as an X-linked recessive trait.

Antihelminthic agent  A substance that inhibits the growth or kills helminth parasites.
Antihistamine  A substance that blocks the effects of histamines in inflammation. A drug that relieves symptoms of allergy.
Anti-idiotype antibodies Antibodies that recognise the binding sites of other antibodies. As a result of the recognition, a network of antibodies is formed all of which can bind to one another, thereby regulating the immune response.

Some allergic responses can be attributed to a breakdown of this regulation.
Antimetabolites Analogues of nucleic acid precursors that are incorporated into nucleic acids in place of the normal precursors. Cytosine arabinoside (Ara-C) is analogue of deoxycytidine that is incorporated into DNA. It kills cells in S phase and also blocks cells in the G1-S boundary, thereby preventing these cells from entering the S phase. 5-Fluorouracil (5-FU) is an analogue of uracil. The phosphorylated derivative binds to thymidylate synthetase and blocks dTMP formation and DNA synthesis. 6-Mercaptopurine, an analogue of hypoxanthine is metabolised to 6-thioinosine monophosphate (6-thio-IMP) which blocks key steps in purine biosynthesis. Some antimetabolites are capable of binding tightly to vital enzymes and inhibiting their function. For example, methotrexate binds tightly to the enzyme dihydrofolate reductase (DHFR) that catalyses the conversionof dihydrofolate to tetrahydrofolate required for 1-carbon metabolism (purine and thymidylate synthesis).

Antibody-producing cell A plasma cell that secretes an antibody with specificity for one antigen.
Anticoagulant A substance that prevents clotting of blood.
Anticoding strand The strand of DNA used as a template for RNA synthesis. Also called the antisense or template strand.
Anticodon Sequence of three nucleotides in tRNA complementary to a specific codon in and mRNA.

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