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The trans form is preferred overwhelmingly in most peptide bonds (roughly 1000:1 ratio in trans:cis populations). However, X-Pro peptide groups tend to have a roughly 30:1 ratio, presumably because the symmetry between the C α and C δ atoms of proline makes the cis and trans isomers nearly equal in energy, as shown in the figure below.
Alterations in translation of mRNA into proteins rapidly modulates the proteome without changing upstream steps such as transcription, pre-mRNA splicing, and nuclear export. [1] The strict regulation of translation in both space and time is in part governed by cis-regulatory elements located in 5′ mRNA transcript leaders (TLs) and 3 ...
Cis-regulatory elements (CREs) or cis-regulatory modules (CRMs) are regions of non-coding DNA which regulate the transcription of neighboring genes.CREs are vital components of genetic regulatory networks, which in turn control morphogenesis, the development of anatomy, and other aspects of embryonic development, studied in evolutionary developmental biology.
Peptide bonds to proline, and to other N-substituted amino acids (such as sarcosine), are able to populate both the cis and trans isomers. Most peptide bonds overwhelmingly adopt the trans isomer (typically 99.9% under unstrained conditions), chiefly because the amide hydrogen (trans isomer) offers less steric repulsion to the preceding C α ...
A polyproline helix is a type of protein secondary structure which occurs in proteins comprising repeating proline residues. [1] A left-handed polyproline II helix (PPII, poly-Pro II, κ-helix [2]) is formed when sequential residues all adopt (φ,ψ) backbone dihedral angles of roughly (-75°, 150°) and have trans isomers of their peptide bonds.
The activation energy required to catalyse the isomerisation between cis and trans is relatively high: ~20kcal/mol (cf. ~0kcal/mol for regular peptide bonds). Unlike regular peptide bonds, the X-prolyl peptide bond will not adopt the intended conformation spontaneously, thus, the process of cis-trans isomerization can be the rate-limiting step ...
Very often, cis–trans stereoisomers contain double bonds or ring structures. In both cases the rotation of bonds is restricted or prevented. [4] When the substituent groups are oriented in the same direction, the diastereomer is referred to as cis, whereas when the substituents are oriented in opposing directions, the diastereomer is referred to as trans.
The double bond in the trans isomer is very strained. [3] The directly attached atoms on a simple alkene are all coplanar. In trans -cycloheptene, however, the size of the ring makes it impossible for the alkene and its two attached carbons to have this geometry because the remaining three carbons could not reach far enough to close the ring ...