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Stichting Food-Info> Topics > Food components > Protein

Proteins, Amino Acids, Peptides, and Polypeptides


Proteins are one of the most important components of animals and plants. All enzymes, most hormones, a large part of our immune system, all muscles and many other body tissues consist of protein.

Peptides (small proteins) and proteins regulate metabolism and provide structural support. Insufficient protein in the diet may prevent the body from producing adequate levels of peptide hormones and structural proteins to sustain normal bodily functions.

Deficiency of good quality protein in the diet may contribute to seemingly unrelated symptoms such as blood pressure problems, fatigue, obesity, diabetes, frequent infections, digestive problems, and bone mass loss leading to osteoporosis. Severe restriction of dietary protein causes kwashiorkor which is a form of malnutrition characterized by loss of muscle mass, growth failure, and decreased immunity.

Many structures of the body are formed from protein:

  • Hair and nails are made of keratins which are long protein chains containing a high percentage (15%-17%) of the amino acid cysteine. Keratins are also components of animal claws, horns, feathers, scales, and hooves.
  • Collagen is the most common protein in the body and comprises approximately 20-30% of all body proteins. It is found in tendons, ligaments, and many tissues that serve structural or mechanical functions. Collagen consists of amino acid sequences that coil into a triple helical structure to form very strong fibers. Gelatin is produced by boiling collagen for a long time until it becomes water soluble and gummy.
  • Tooth enamel and bones consist of a protein matrix (mostly collagen) with dispersed crystals of minerals such as apatite, which is a phosphate of calcium.
  • Muscle tissue consists of approximately 65% actin and myosin, which are the contractile proteins that enable muscle movement.
  • Casein is a nutritive phosphorus-containing protein present in all animal milk. It makes up approximately 80% of the protein in all animal milk and contains all the common amino acids.

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