at Related Biological Terms:
A reference to the base composition of double-stranded DNA. DNA from different sources has different ratios of the A-to-T and G-to-C base pairs, e.g. DNAs isolated from organisms that live in hot springs have a higher GC content, which takes advantage of the increased thermal stability of the GC base pair. (see also Chargaff's rule)
A model that accounts for chromosomal banding. The microscopic appearance of chromosomes during mitosis (metaphase) displays chromomeres and interchromomeres, i.e. G bands (Giemsa stain) and R bands (Reverse) respectively; the former are characterized as AT-rich and gene-poor and by late replication, and the latter as GC- and gene-rich and by early replication. The DNA is presumably organized into wide spring-like coils from which 100kb G loops extend parallel to the chromosome axis (G bands), extended DNA sequences from which larger loops extend perpendicular to the chromosome axis (R loops), and AT-rich sequences called matrix-attachment or scaffold-associated regions that anchor the G and R loop regions and create the characteristically stained bands. Gardiner, K. (1995) Curr. Opin. genet. Dev. 5, 315-322
One of a minority of introns which have at their 5'- and 3'-termini, respectively, the AT and AC sequences. They are excised by a mechanism similar to that for the more common GU-AG introns.Nilsen, T.W. (1996) Science 273, 1813
An enzyme that hydrolyses ATP; usually the partial activity of an enzyme, or system of enzymes, that uses the energy made available by the hydrolysis of ATP to drive an energetically unfavourable process, e.g. the Na+/K+-ATPase of cell membranes.
The actual, as opposed to relative to some other compound, orientation of atoms in space at an asymmetrical centre.
(= facilitated diffusion)
The observation, first based on inspection of structures, later on experimentation, that many natural products appear to have been assembled from multiple acetate (acetyl-CoA and/or malonyl-CoA) units in head-to-tail condensations. (see also acetogenin; polyketide; propionate rule)
In immunology, the immune response of an organism to a foreign substance; lack of a response is called tolerance.
The energy needed to raise the reactants, or an enzyme-substrate complex, to the transition state, where it has an equal likelihood of conversion to product or reversion to reactants. This value is commonly evaluated in an Arrhenius plot, lnk against 1/T, where k is the rate constant, T is the absolute temperature and the slope is Ea/R (Ea is the activation energy and R the gas constant). (see also Q10; reaction co-ordinate)
In enzyme kinetics, a compound that increases the rate of an enzymic reaction. (see also allostery)
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