Proteins

The amino acids in proteins are joined together by peptide bonds to form polypeptide chains; a protein consists of one or more polypeptide chains. Like nucleic acids, polypeptides have polarity under physiological conditions: one end (often called the amino end) has a free amino group (NH3+) and the other end (the carboxyl end) has a free carboxyl group (COO−). Proteins consist of 50 or more amino acids; some have as many as several thousand.