THE Planar Peptide Bonds PDF

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THE PLANAR PEPTIDE BONDS The acid amide bond is very special: it has two C atoms as substituents, namely the C α atoms of the two amino acids involved in the bond. The limited turnover of the peptide bond results in 6 atoms coming to lie in one plane, namely O=C-N-H and the two C α, with the two single bonds C α -CO and N- C α being free to rotate. It would not have to be this way, it could also take another given rigid structure, but the bond orbitals of the atoms involved cause this very plane. The two Cs lie in the same plane, but the bonds are free to rotate along their axis. This in turn causes only the respective peptide bond planes to be rotatable with respect to each other, as whole planes, but otherwise the mobility is very limited. Therefore, a sequence of amino acids cannot occupy any structure, but only certain structures. (Angle Phi Ф and Psi Ψ). Between them are now arranged the side chains, this imposes the following restrictions to which an amino acid polymer of this type is subject: Loud planes, in which 6 atoms have to lie, between them side chains of different length, different size, different flexibility. Glycine for example: with its H atom will hardly cause a restriction of the possible angles.

SHORT AMINO ACID CHAINS (PEPTIDES) Since the condensation products of amino acids are linear polymers, proteins can be represented as amino acid sequences. Such sequences are notated by convention from the amino-terminal to the carboxyl-terminal end. A short chain of Aa might then look like this. Longer chains are then no longer arranged in such a linear fashion, with no internal interactions or structure, but have a distinct structure due to intramolecular interactions, which is even reflected in crystals. However, the limitations shown for peptide bonds mean that only certain structures are possible....