Peptidkette

Peptidkette is the term used for a linear sequence of amino acids that are linked by peptide bonds. The chain has an N-terminus, with a free amino group, and a C-terminus, with a free carboxyl group. In biochemistry the peptidkette forms the basic structural element of proteins, while shorter chains are referred to as peptides or oligopeptides and longer chains as polypeptides or proteins. The order of amino acids in the chain determines its chemical properties and biological function.

Peptidbindungen are formed by condensation reactions between the carboxyl group of one amino acid and the amino group of the adjacent one, resulting in a planar, resonance-stabilized bond. The peptidkette is directional, progressing from the N-terminus to the C-terminus. In cells, the linear chain may fold into higher-order structures and, if present, can be stabilized by disulfide bridges between cysteine residues or undergo post-translational modifications that influence activity and stability.

Types and size categories vary with length. Dipeptides contain two amino acids, tripeptides three, and oligopeptides extend to a few dozen residues; longer sequences are called polypeptides and, when properly folded, can form enzymes, receptors, or structural proteins. Some peptidketten are cyclic, and modifications or cross-links can alter their properties.

Biosynthesis occurs primarily on ribosomes through mRNA-directed translation, but non-ribosomal peptide synthesis also exists in microorganisms for certain secondary metabolites. Peptidketten can be synthesized chemically, for example by solid-phase peptide synthesis. They are degraded by proteases, releasing amino acids for reuse.

Functions of peptidketten are diverse, including signaling (hormones and neuropeptides), regulation, antimicrobial activity, and as components of enzymes and structural proteins. Peptidketten are fundamental to biochemistry, medicine, and biotechnology.