at Related Biological Terms

A form of secondary structure of a protein in which the amide hydrogens of a peptide bond of one extended polypeptide sequence are shared with the carbonyl oxygens of a peptide bond on a second polypeptide sequence. A sheet that often consists of three or more polypeptide sequences is said to be parallel (i.e. both adjacent strands run in the same direction; N- to C-terminal) or antiparallel.

An inhibitor of a hydrolase that incorporates structural features of both products of catalysis, and thus can bridge the S1 and S1' subsites. (see also specificity subsite)

A method for determination of zygosity. Two sets of primers are used. Of the inner set, primer A is complementary to a point mutation on the coding strand and primer B is complementary to the wild-type non-coding strand. The outer set of primers, P and Q, flank the mutation site on the coding and non-coding strands, respectively. P and Q are chosen so that the amplicons PB and AQ will have characteristic lengths. The pattern of PCR products is informative of the zygosity of the tested genomic DNA: all samples will generate PQ; the heterozygote and the homozygous wild-type will generate PB and the heterozygote and homozygous mutant will generate AQ. A and B are designed to mismatch the unintended allele at their 3' ends and they possess G+C-rich tails. The efficiency of replication is affected by template transfer: as replication of an amplicon proceeds, it replaces genomic DNA as the template. In bi-PASA, as PQ accumulates, it also can serve as a template for amplification of the shorter fragments. This is contrasted with self amplification, which occurs when the shorter templates replicate only themselves. Self amplification is favored by the G+C-rich tails and by annealing conditions that discourage all but the stronger G-C bonds. Basically similar to bi-PASA is tetra-primer PCR, in which the internal set of primers are mismatched in the middle of their sequences, and they lack G+C-rich tails. This variation requires high- and low-stringency annealing conditions to generate appropriate amounts of the three potential amplicons, whereas bi-PASA uses a constant annealing temperature.Lu, Q., Thorland, E.C., Heit, J.A. and Sommer, S.S. (1997) genome Res. 7, 389-398

Synthesis of DNA that is effected by two replication forks that travel away from a single origin of replication.

The management, manipulation and use of DNA nucleotide sequences, and consequent protein amino acid sequences, that are known from sequencing of genomes and cDNA librariesAndrade, M.A. and Sander, C. (1997) Curr. Opin. Biotechnol. 8, 675-683; Ashburner, M. and Goodman, N. (1997) Curr. Opin. Genet. Dev. 7, 750-756

Processes that use the capabilities of micro-organisms to treat waste products that may be environmentally harmful and to render them innocuous.

(see chair form)

A technique similar to PCR that also uses a heat-resistant polymerase and cycles of polymerization, denaturation and annealing, but which requires only one primer. The source DNA is digested with a restriction endonuclease. A universal adaptor is engineered with self-complementary sections, so that it loops back upon itself and has ends that permit ligation to both strands at each end of the restriction fragment. In the first amplification cycle a primer anneals to an internal site and the polymerase copies the primer-binding strand through the adaptor, back along the second strand and past the site that is complementary to the primer-binding site of the first strand. In subsequent cycles the primer will have two sites for initiation of polymerization. Hengen, P.N. (1995) Trends Biochem. Sci. 20, 372-373

(see Holliday model)

A variant of C3 photosynthesis in which CO2 is first concentrated at the site of photosynthesis by carboxylation of phosphoenolpyruvate to oxaloacetate, which is then transported as such or as an interchangeable 4-carbon dicarboxylic acid to the site of photosynthesis. This is an advantage to the plant because the key enzyme, ribulose bisphosphate carboxylase, which in photosynthesis forms 2 mol of 3-phosphoglycerate, has a competing activity, O2 photorespiration, which produces both 3-phosphoglycerate and phosphoglycolate. (see also C3-C4 photosynthesis)Rawsthorne, S. (1992) Essays Biochem. 27, 135-146