one and one-half syndrome
| evolution, molecular | Evolution at the molecular level of DNA sequences and proteins. (rieger et al., glossary of genetics: classical and molecular, 5th ed) (12 Dec 1998) |
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| kinetic molecular theory | <chemistry> This theory assumes that molecules must collide in order to react. The more collisions the more likely it is for a reaction to occur. However, depending on the conditions, only a small fraction of the collisions are effective in producing a reaction. There are several constraints. In order for a reaction to occur, bonds initially are broken, which requires energy. This energy depends on the type of the reaction and comes from the kinetic energies that the molecules possess before the collision. It is called the activation energy. Increasing the temperature increases the kinetic energies and more collisions will occur. In adition, at a higher temperature a greater number of the reacting molecules might possess an energy equal to or greater than the activation energy. However the molecules must also collide in a specific orientation, called the steric factor in order for a reaction to occur. A reaction will only be successful, if the collision has enough energy to be either equal to or greater than the activation energy and if the orientation of the collision allows for correct bond formation. These factors are in the Arrhenius equation: k = zp The rate constant k is proportional to the Arrhenius factor A. A is the product of the collision frequency z, and the steric factor p. The fraction of collisions with sufficient energy to produce a reaction are in the term of the equation. (09 Jan 1998) |
| kininogen, high-molecular-weight | A plasma protein, molecular weight of 110 kD, that normally exists in plasma in a 1:1 complex with prekallikrein. Hmwk is split by plasma kallikrein to produce bradykinin. The complex is a cofactor in the activation of coagulation factor xii. The product of this reaction, xiia, in turn activates prekallikrein to kallikrein. (12 Dec 1998) |
| kininogen, low-molecular-weight | A protein, molecular weight 50 kD, located in various normal tissues. Upon cleavage by kallikrein or other kallikreins, it forms kallidin. Kallidin, in turn, is converted into bradykinin. (12 Dec 1998) |
| abstracting and indexing | Shortening or summarizing of documents; assigning of descriptors for referencing documents. (12 Dec 1998) |
| academies and institutes | Organizations representing specialised fields which are accepted as authoritative; may be non-governmental, university or an independent research organization, e.g., national academy of sciences, brookings institution, etc. (12 Dec 1998) |
| accounts payable and receivable | Short-term debt obligations and assets occurring in the regular course of operational transactions. (12 Dec 1998) |
| aged, 80 and over | A person 80 years of age and older. (12 Dec 1998) |
| algae and fungi | Algae represent a group of spore-propagating plants, unicellular or undifferentiated into root, stem, and leaf. They include seaweed and many unicellular fresh water plants, most of which contain chlorophyll. They account for about 90% of the earth's photosynthetic activity. Fungi are eukaryotic, heterotrophic organisms that live as saprobes or parasites and include mushrooms, yeasts, smuts, molds, etc. They lack chlorophyll. (12 Dec 1998) |
| alkyl and aryl transferases | <enzyme> A somewhat heterogeneous class of enzymes that catalyze the transfer of alkyl or related groups (excluding methyl groups). Registry number: EC 2.5 (12 Dec 1998) |
| allergy and immunology | A medical specialty concerned with the hypersensitivity of the individual to foreign substances and protection from the resultant infection or disorder. (12 Dec 1998) |
| alligators and crocodiles | Large, long-tailed reptiles, including caimans, of the order loricata. (12 Dec 1998) |
| Amine Precursor Uptake and Decarboxylation | <pharmacology, physiology> Paracrine cells of which argentaffin cells are an example. Usage of the term APUD is neither helpful nor memorable. Acronym: APUD (11 Nov 1997) |
| amino acids, peptides, and proteins | Amino acids and chains of amino acids connected by peptide linkages. (12 Dec 1998) |
| Anderson and Goldberger test | A test for typhus in which the patient's blood is injected into a guinea pig's peritoneal cavity. In typhus a typical temperature curve will be observed. (05 Mar 2000) |