at Related Biological Terms

In chemical kinetics, the hypothetical state that is mid-way between reactants and products, poised at a point where the reaction is as likely to go forward to products as it is to fall back to reactants. If the reactants and transition state may be considered to be in equilibrium, application of the second law of thermodynamics allows analysis of the temperature-dependence of reaction rates. The concept may be applied to enzyme kinetics to describe the transition from enzyme-substrate complex to enzyme-product complex.

An enzyme inhibitor that is designed to fit the transition state of an enzyme, as opposed to one that is a substrate analogue; characterized by a very low dissociation constant.

The temperature at which the plasma membrane undergoes a phase transition, due to the increased mobility at higher temperatures of the fatty acyl chains of phospholipids.

The synthesis of a protein directed by mRNA.

In genetics, the movement of a portion of one chromosome to another; in protein synthesis, the transfer of the newly elongated peptidyl-tRNA from the amino acyl site to the peptide site of a ribosome; in cell biology, the movement of a molecule across a barrier or between cytosol and membrane surface.

Transmethylation is a biologically crucial organic chemical reaction in which a methyl group is transferred from one compound to another. Transmethylation can also be regarded as a transfer of a methyl group from one compound to another; e.g., l-homocysteine is converted to l-methionine by the transfer to the latter of a methyl group. The mechanism of transmethylation was then examined. A series of deuterium-labeled methylated compounds were synthesized by du Vigneaud's group, including arsenocholine, trimethylamine, dimethylglycine, and dimethylthetin. Of these, only betaine and dimethylthetin served as methyl donors. In 1949, Dubnoff found that choline could only act as a donor under aerobic conditions when it was oxidized to betaine. A vital metabolite for most transmethylation reactions of the body is SAM. It is generated directly from methionine by a reaction catalyzed by MAT.

A single base change that does not result in an altered protein, due to the degeneracy of the genetic code, i.e. the mutation is from one codon to another for the same amino acid. (see also silent mutation)

A characteristic of some proteinases; the transfer of one product of the catalytic cleavage to another peptide rather than to water; the transfer of the N-terminal fragment to the amino group of an acceptor peptide or the transfer of the C-terminal fragment to the carboxyl group of an acceptor; the former often, but not exclusively, due to an acyl-enzyme intermediate in the catalytic cycle.

An excited electronic state in which an electron is raised to a higher energy level and its spin is reversed, which prevents its easy collapse to the ground state. Such collapse is sometimes accompanied by phosphorescence. (see also singlet state)

In molecular biology, truncation refers to the process of shortening a molecule or sequence by removing a portion of it. This can refer to DNA, RNA, proteins, or other biological molecules. Truncation can occur naturally or through laboratory techniques. Natural truncation can occur through various processes, such as alternative splicing of RNA transcripts or degradation of proteins by proteases. These processes can result in removing specific domains or regions of the molecule, altering its function or activity. In the laboratory, truncation can be used as a technique to study the function of specific domains or regions of a molecule. For example, a protein containing multiple domains can be truncated to remove one or more domains, allowing researchers to study the function of the remaining domains in isolation. Truncation can also be used to create mutant forms of a molecule with altered activity or specificity. In DNA sequencing, truncation can occur when the sequencing reaction is terminated prematurely, resulting in a partial sequence of the DNA fragment. This can be useful for identifying the presence of specific DNA sequences or mutations, but may not provide a complete picture of the target sequence. Truncation can also occur in >protein expression