The role of proteins in biology.

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The role of proteins in biology

Proteins are an extremely important group of molecules in living organisms. They have a number of important functions. For example:

  • Important for growth and repair
  • They are an essential part of cell membranes
  • Help to transport things around the body
  • Antibodies which fight invading micro organisms are proteins
  • All enzymes are proteins

  Many proteins don’t coil but form long chains. These are called fibrous proteins. Collagen is a fibrous protein and an important structural protein. It consists of three polypeptide chains, each in the shape of a helix. The three wind around each other like a rope (see diagram a- a computer graphic of collagen). As almost every third amino acid in each polypeptide is glycine, its small shape allows the strands to lie in a close coil. These strands are held together by hydrogen bonds. The complete three-stranded molecule interacts with collagen molecules running parallel to it. Bonds are formed between adjacent molecules so fibres are established. The parallel molecules are staggered at the ends, staggering of molecules prevents weak spots; hence its strength. The Achilles tendon, which is almost all collagen fibres, can withstand a pulling force of300 N per mm2 of a cross-sectional area, around one-quarter the tensile strength of mild steel. Collagen in our cartilage and tendons gains its strength from its three-stranded, rope-like structure. There are 21 known collagens, and each serves a specific role in a wide variety of tissues including bone, teeth, skin, tendons, cartilage and blood vessels.

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The major ones are:

  • Type I. The chief component of tendons, ligaments, and bones.
  • Type II. Represents more than 50% of the protein in cartilage. It is also used to build the notochord of vertebrate embryos.
  • Type III. Strengthens the walls of hollow structures like arteries, the intestine, and the uterus.
  • Type IV. Forms the basal lamina of epithelia. (The basal lamina is often called the basement membrane, but is not related to lipid bilayer membranes.) A meshwork of Type IV collagens provides the filter for the blood capillaries.

  A protein ...

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