Collagen

Collagen

Collagen is the most abundant protein in the animal kingdom. Approximately one third of the protein in a mammal’s body is collagen. It makes up a major portion of the connective tissue found in skin, joints, ligaments, muscles, ten-dons, and bones. Different types of collagen occur in different species. That is, the collagen found in humans is somewhat different from that found in cows, and both human and cow collagen differ from the collagen found in other animals, such as dogs and ats. Nonetheless, all forms of collagen have a common molecular structure that consists of three rope-like strands intertwined with each other. Each strand (called tropocollagen) is a polymer consisting of amino acids, the most common of which are glycine, proline, and hydroxyproline. Collagens differ from each other in regard to the relative amounts of each amino acid present.

HOW IT IS MADE

Collagen is synthesized in the bodies of all higher verte-brates in a complex series of reactions that begin with the linking of amino acids with each other. Amino acids are organic compounds that contain both the carboxyl group (-COOH) and the amino group (-NH2). The amino acids are joined to each other in very long chains known as polypeptides (a word meaning ‘‘many amino acids’’). After assembly, polypeptide chains intertwine with each other in groups of three to make large molecules called procollagen (‘‘early collagen’’), which is then cut into smaller pieces by enzymes designed especially for that purpose. The three strands that make up each collagen group are held together by the action of vitamin C molecules.

COMMON USES AND POTENTIAL HAZARDS

All of the connective tissue in the body contains collagen. This collagen is flexible but not stretchy and will tear if pulled to strongly. Collagen is also a primary component of cartilage, the material that fills the gaps between bones and fills out structures that are firm but somewhat soft, such as the end of the nose and ears. There are at least a dozen types of collagen in the body, each one with a slightly different physical and chemical structure.

Type I is the most abundant kind of collagen. It forms long strands that criss-cross the spaces between cells and is found throughout the body, particularly in tendons, bones, and scars. Type II collagen is found in cartilage, and Type III collagen in granulation tissue that forms when wounds heal. Type IV collagen comprises the basal lumina, the membrane that supports skin and internal surfaces. The eight other types of collagen all have their specific functions in the body.

Plastic surgeons use collagen to fill wrinkles and lines in their patients’ faces and bodies. As people age, the tissue that fills out their faces and makes the skin look smooth and tight breaks down, leaving lines and wrinkles. Injecting collagen into wrinkles fills the area under the skin with tissue that puffs out the skin, making it firm and smooth again. Doctors also use collagen to fill in scars. In most cases, collagen treatments are not permanent. The collagen breaks down or is absorbed and additional treatments are necessary to remove wrinkles.

Several health disorders result from inadequate or abnor-mal collagen in the body. Scurvy, caused by a deficiency of vitamin C, is the best known of these. When adequate amounts of vitamin C are not present in the body, collagen molecules break apart and muscles and joints are damaged. Ehlers-Danlos syndrome is a disorder that occurs when collagen molecules are weakened, causing bruising of the skin, rupture of arteries or intestines, overly flexible joints, skin and bone deformities, and hip dislocations. Osteogenesis imperfecta results in poorly formed bones and causes the sclera (the white part of the eye) to turn blue.