| pyrimidine dimer | <biochemistry> A dimer product found in DNA chains damaged by ultraviolet irradiation. Most frequently thymidine dimers. They consist of two adjacent pyrimidine nucleotides, usually thymine nucleotides, in which the pyrimidine residues are covalently joined by a cyclobutane ring. These dimers stop DNA replication. (21 Jun 2000) |
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| d-dimer test | Test that detects the cross-linked fibrin degradation fragment, D-dimer. Elevations in this fragment are seen in primary and secondary fibrinolysis, during thrombolytic or defibrination therapy with tissue plasminogen activator, as a result of thrombotic disease, such as deep-vein thrombosis, pulmonary embolism or DIC, in vasoocclusive crisis of sickle cell anaemia, in malignancies, and in surgery. (05 Mar 2000) |
| dimer | A molecule which consists of two similar (but not necessarily identical) subunits. The term could also be used as a verb referring to the act of the two subunits coming together (to dimerize). (09 Oct 1997) |
| thymine dimer | <molecular biology> Dimer that can be formed in DNA by covalent linkage between two adjacent (cis) thymidine residues, in response to ultraviolet irradiation. Occurrence potentially mutagenic, although repair enzymes exist that can excise thymine dimers. See: xeroderma pigmentosum. (18 Nov 1997) |
| peptide chain initiation | The process whereby the formation of a peptide chain is started. This process requires (1) the 30s subunit, (2) the mRNA coding for the polypeptide to be made, (3) met-trnai, (4) initiation factors, and (5) GTP. (12 Dec 1998) |
| peptide initiation factors | Protein factors uniquely required during the initiation phase of protein synthesis. (12 Dec 1998) |
| initiation | 1. The first stage of tumour induction by a carcinogen; subtle alteration of cells by exposure to a carcinogenic agent so that they are likely to form a tumour upon subsequent exposure to a promoting agent (promotion). 2. Starting point of replication or translation in macromolecule biosynthesis. 3. Start of chemical or enzymatic reaction. (05 Mar 2000) |
| initiation codon | The codon 5' AUG in mRNA, at which polypeptide synthesis is started. It is recognised by formylmethionyl tRNA in bacteria and by methionyl tRNA in eukaryotes. (18 Nov 1997) |
| initiation complex | Complex between mRNA, 30S ribosomal subunit and formyl methionyl tRNA that requires GTP and initiation factors to function. (18 Nov 1997) |
| initiation factor | One of several soluble proteins involved in the initiation of protein or RNA synthesis. (05 Mar 2000) |
| initiation factors | The set of catalytic proteins required, in addition to mRNA and ribosomes, for protein synthesis to begin. In bacteria three distinct proteins have been identified: if 1 (8 kD), IF 2 (75 kD) and IF 3 (30 kD). at least 6-8 proteins have been identified in eukaryotes. IFs 1 and 2 enhance the binding of initiator tRNA to the initiation complex. (18 Nov 1997) |
| initiation tRNA | TRNA in prokaryotes containing a formyl-methionyl residue that initiates translation. Synonym: formyl-methionyl-tRNA, starter tRNA. (05 Mar 2000) |
| tumour initiation | <cell biology, oncology> First stage of tumour development. See: tumour progression. (18 Nov 1997) |
| acute post-streptococcal glomerulonephritis | <nephrology> A disease of the kidneys that results in inflammation of the glomerulus (the portion of the kidney that filters the blood). Conditions which may cause glomerulonephritis include post-streptococcal disease (strep throat), lupus, syphilis, bacterial endocarditis, membranoproliferative glomerulonephritis, sepsis, vasculitis, Goodpasture's syndrome, typhoid fever, Henoch-Schonlein purpura, hepatitis or a viral infection (for example mumps, measles, mononucleosis). (27 Sep 1997) |
| RNA processing, post-transcriptional | Post-transcriptional biological modification of messenger, transfer, or ribosomal rnas or their precursors. It includes cleavage, methylation, thiolation, isopentenylation, pseudouridine formation, conformational changes, and association with ribosomal protein. (12 Dec 1998) |