Peptides are formed when two or more amino acids bond together through a peptide bond, also known as an amide bond. This bond occurs when the carboxyl group of one amino acid covalently links with the amino group of another amino acid. In this process, the carboxyl group is typically in its anionic form (negatively charged), while the amino group is in its cationic form (positively charged).

The formation of a peptide bond involves a condensation reaction, where water is lost. For example, when the amino acids alanine and threonine combine, a molecule of water is released. Specifically, this involves the loss of one oxygen atom and two hydrogen atoms from the amino group, resulting in the formation of the peptide bond. The remaining structure retains one hydrogen on the nitrogen, while the carbonyl group remains intact. The resulting compound is referred to as a dipeptide, which can be represented by the three-letter codes of the amino acids connected by a hyphen (e.g., Ala-Thr).

The nomenclature for peptides is based on the number of amino acids they contain. A dipeptide consists of two amino acids, a tripeptide consists of three, and a tetrapeptide consists of four. When the chain of amino acids exceeds four, it is generally referred to as a polypeptide, which is a larger chain of amino acid residues. Each individual amino acid within a peptide is termed a residue.

In summary, peptides are essential biological molecules formed through the linkage of amino acids via peptide bonds, with the process involving the loss of water and the formation of various types of peptides based on the number of amino acids involved.

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