Simplified Chemistry

صبغ يتميز بالألفة تجاه الحموض النووية. فمعقد الحمض النووي مع الصبغ يشع اللون البرتقالي عند ارتباطه ب RNA و بالأخضر مع DNA و ذلك عند رؤيته بالمجهر الفلورنسي . الصيغة الكيميائية لهذه المادة C17H19N3 و وزنها الجزيئي 265.35 .

acridine the parent compound of a series of derivatives, e.g. 3,6-diaminoacridine (proflavin), that are potent mutagens. Some acridines are found in coal tar. They induce frameshift mutations during the replication of DNA by binding to DNA and distorting the double helix, causing additional bases to be incorporated or bases to be omitted. They are used as topical antiseptics and antimalarial …

ackee or akee a tree, Blighia sapida, native to tropical Africa and widely cultivated in the West Indies, especially Jamaica, for its fruit, the fleshy aril of which is edible when cooked and forms an important item of local diet. Unripe fruits contain toxic amounts of hypoglycin and can cause Jamaican vomiting sickness.

acid phosphatase , systematic name: orthophosphoric monoester phosphohydrolase (acid optimum); other names: alkaline phosphomonoesterase; phosphomonoesterase; glycerophosphatase; a lysosomal enzyme (except in red cells). It catalyses the hydrolysis of orthophosphoric monoester to an alcohol and orthophosphate. Zinc and magnesium are cofactors. It is present in high concentrations in the prostate gland, and is also present in red cells, platelets, bone, liver, …

acid dissociation constant or acidity constant symbol: Ka; the thermodynamic equilibrium constant for the dissociation of an acid. For a dilute solution of a weak acid, HA, dissociating in water according to the equilibrium: HA + H2O  ↔ H3O+ + A–, Ka = (aH3O+ × aA–)/aHA where a is the activity of the species designated by the subscripts. The activity …

acid ceramidase , other name: N-acylsphingosine deacylase; a lysosomal enzyme that catalyses the hydrolyis of ceramide to sphingosine and a fatty acid. Its activity requires sphingolipid activator proteins (i.e. saposins B and C) and negatively charged phospholipids. A genetic locus at 8p21.3-22 encodes a precursor that contains 395 amino acids and is proteolytically cleaved into an a subunit (≈13 kDa) …

acetyl coenzyme A or acetyl-CoA; a derivative of coenzyme A in which the sulfhydryl group is acetylated. Originally termed ‘active acetate’, it is an important metabolite, derived from pathways such as glycolysis, fatty-acid oxidation, and degradative metabolism of some amino acids. It is further metabolized by the tricarboxylic- acid cycle and represents a key intermediate in lipid and terpenoid biosynthesis …

acetylcholinesterase ,systematic name: acetylcholine acetylhydrolase; other names: true cholinesterase; cholinesterase I; an esterase enzyme that catalyses the hydrolysis of acetylcholine to choline and acetate; it also acts on a variety of acetic esters and catalyses transacetylations. It is found in or attached to cellular or basement membranes of presynaptic cholinergic neurons and postsynaptic cholinoceptive cells. A soluble form occurs in …

A naturally occurring quaternary ammonium cation ester, with the formula CH3(O)COC2H4N(CH)3+, that plays a prominent role in nervous system function. The great importance of acetylcholine derives from its role as a neurotransmit­ter for cholinergic neurons, which innervate many tissues, including smooth muscle and skeletal muscle, the heart, ganglia, and glands. The effect of stimulating a cholinergic nerve, for example, the …

accessory pigment any of the, such as the yellow, red, or purple carotenoids and the red or blue phycobiliproteins in photosynthetic cells. The carotenoids are always present, whereas the phycobiliproteins occur only in algae belonging to the Rhodophyceae, the Cyanophyceae, and the Cryptophyceae. Strictly speaking, chlorophyll b is also an accessory pigment.