Peptides and polypeptides are both chains of amino acids. Your endocrine system secretes peptides and polypeptides. After they are secreted, your blood distributes peptides and polypeptides to end organs such as your heart, kidneys and liver. Endocrine organs involved in this secretion process include your thyroid gland, hypothalamus, pituitary gland, adrenals, endocrine pancreas, adipose tissues and ovaries.
Peptides and polypeptides are amino acid chains of various lengths. A peptide contains two or more amino acids, and a polypeptide, on the other hand, contains ten or more amino acids. Peptide bonds hold together both peptides and polypeptides. The T cells in your body recognize peptides and polypeptides as very small proteins. Additionally, some pharmaceutical products use peptides and polypeptides in vaccines to stimulate antibody production.
Twenty amino acids form the building blocks for proteins. Amino acids chemically stick together by forming peptide bonds. You can call any string of two or more amino acids a peptide. Thus, a polypeptide is a type of peptide. Further, dipeptides, tripeptides and tetrapeptides respectively hold two, three and four amino acids. An oligopeptide is the general term for peptides containing 12 to 20 amino acids. Peptides also rarely contain strings of more than 30 amino acids.
Biochemists generally use the term polypeptide to describe medium-size peptide chains consisting of 10 or more amino acids. In biochemistry, the term protein is nonspecific, because it includes amino acid chains of any length. However, polypeptides refer to proteins of a particular size. Therefore, the term polypeptide refers to a general size of peptide chains. The pancreatic hormone insulin is an example of a polypeptide. Insulin helps your body to use and store sugar.
Peptides and polypeptides are both proteins, but biochemists do not generally describe peptides and polypeptides using the generic term protein. Further, biochemists normally only use the word protein when referring to large peptide molecules. They could either contain a long, single amino acid chain or consist of several amino acid chains joined together. An example of a large protein is hemoglobin. Your red blood cells contain hemoglobin, and this protein holds four amino acid chains.