Biochemistry

According to the number of amino acid residues, dipeptides, tripeptides, tetrapeptides, etc. are distinguished. Peptides containing from two to ten residues are called oligopeptides. Peptides consisting of more than ten amino acid residues are polypeptides. The beginning of the polypeptide chain is considered to be an amino acid with a free a-amino group (N is a terminal amino acid), and the end is an amino acid with a free carboxyl group (C is a terminal amino acid). The name of the peptides consists of the name of the first amino acid with a typical acyl ending for -yl, the names of subsequent amino acids (also with the ending -уГ) and the full name of the last amino acid. For example, the tripeptide below is called asparaginyl-glycyl- phenylalanine or Asn-Gly-Phe for short, or H-Asn-Gly-Phe-OH (abbreviated entry). TRIPEPTIDE N-end asparagmyl glycyl phenylalanine ? I? h 2 n - ch - c - nh - ch 2 - c - nh - ch - cooh CH 2 -CO-NH2 сн 2 од z C-end Polypeptide chains consisting of more than 50 amino acids are conventionally called protein. Typically, the molecular weight of such polypeptides is about 6000 Da. The number of amino acid residues in proteins reaches several thousand. In order to understand the structure of giant protein molecules, it is necessary to know the most important types of interaction between individual amino acid residues that stabilize protein molecules at different levels of their organization. Types of chemical bonds in a protein molecule In biomolecules, chemical bonds can be divided into covalent and non- covalent. Covalent bonds include peptide and disulfide bonds. An important role in maintaining the spatial structure of biological molecules is played by weaker than covalent chemical bonds (hydrogen and ionic bonds, van der Waals forces, hydrophobic interactions). Hydrogen bonds. This type of bond appears during the electrostatic interaction of a hydrogen atom with a partially positive charge and a covalently bonded oxygen (nitrogen) atom with a negative charge. The ability to form hydrogen bonds is pronounced in compounds containing -CO, -NH, -OH, -COO- , -COH groups. Protein molecules can have different types of hydrogen bonds. In a protein molecule, hydrogen bonds can form between groups of peptide chains and side chains of amino acids. Hydrogen bonds are intramolecular and 51