There are 3 main types of Protein. Fibrous, Globular and Conjugated.
Fibrous proteins are different from the globular proteins by their long filamentous structure.
The fibrous proteins are the proteins that hold many of the living structures together. Examples of fibrous proteins are elastin, collagen, keratin, actin and myosin. All fibrous proteins have different structural properties, which suit it to the role it plays in the organism’s body. Elastin, Collagen and Keratin are all strong and inelastic. Actin and Myosin however are contractile this meaning that they become shorter and narrower. Proteins are found all over the body. Many spiral-shaped polypeptide molecules becoming linked together in parallel lines by cross-bridges forming between them form the fibrous proteins long rope like structure. Skeletal muscle consists of fibres containing smaller myofibrils. Each myofibril is divided into compartments called sacromeres by membranous partitions. Filament means a slender thread like structure. Each myofibril contains two types of filament. Thick filaments each of which are composed of many molecules of myosin and thin filament, which is composed from many molecules of actin. The arrangement of these filaments produces the striated (striped) effect that is typical of skeletal muscle tissue when it is viewed under a microscope.
Globular proteins like the fibrous proteins consist of several polypeptide molecules joining together, however globular proteins form together into a roughly spherical shape like a tangled ball of string. Globular proteins are vital components of all living things and play a variety of roles. Enzymes, Hormones, Antibodies, Transport Proteins and Structural Proteins are all globular proteins. Intracellular enzymes speed up the rate of biochemical processes such as photosynthesis, respiration and protein synthesis of which are all essential for the maintenance of life. Hormones are chemical messengers of which are made by endocrine glands and then transported through an animals blood to target tissues where they exert a specific effect.
Antibodies are made by white blood cells called lymphocytes and defend the body against antigens (a complex molecule). Transport proteins take substances from one part of the body to another. E.g. transferring goes together with iron, entering the blood stream from the gut or released during the destruction of red blood cells and transports it to the bone marrow for re-use. Structural proteins are made of 2 components, which make up the membrane surrounding a living cell. In the same way it forms an essential part of all membranes possessed by structures within the cell such as the nucleus. There this type of protein plays a very vital structural role in every living cell.
Conjugated proteins consist of a globular protein associated with a non-protein chemical.
- A glycoprotein is made up of protein and carbohydrate. For example: Mucus, which is a slimy, viscous substance secreted by epithelial cells to lubricate or protect parts of the body.
- A lipoprotein is a complex molecule consisting of protein and lipid. Lipoproteins coat the products of fat digestion which are absorbed from the small intestine before being transported round the body.
- Haemoglobin is an oxygen-transporting pigment in blood. We need haemoglobin cells to survive.
All proteins play a wide variety of roles in our bodies and all living cells. Some are part of the cell structure, some are our bodies defence mechanisms, some transport all the essential materials to and fro, whilst others regulate biochemical reactions and metabolic processes.
