The next group, Co-ordinated Motion or Contractile Proteins consists mainly of two fibrous proteins. Actin and Myosin these are needed for muscle contraction. These form two filaments one thick (myosin) and one thin (actin) which have the ability to slide over each other giving contraction. These relationships between two proteins also gives the movement of flagella and chromosomes in mitosis.
In biological terms almost all chemical reactions are catalysed by Enzymes. As such they play a hugely important role in metabolic function. These enzymes are all proteins and thousands of different enzymes have been identified, each acting on a unique substrate. Some of the more common enzymes occur in digestion and excretion: Trypsin, amylase and lipase are all catalysts to hydrolysis reactions. In the case of Trypsin, catalysing the hydrolysis of proteins to polypeptides. Amylase allows the break down of starch to maltose, and the hydrolysis of fats to fatty acids and glycerol is catalysed by lipase. Urease also helps the formation of urea. Other than these few nutritional enzymes, there are many others that catalyse every reaction within every cell of every organism.
Transport and Storage is another function of proteins. Proteins such as Haemoglobin which transports oxygen, allow the transport of many molecular and ionic substances around the body as well as being a medium for the movement of oxygen in the case of myoglobin between individual muscle cells. Storage proteins are formed from other proteins and do not interfere with metabolic functions, for example those present in egg white (Ovalbumin) and milk (Casein).
Antibodies are a very specific group of proteins which are crucial to the immune response. The antibodies can combine with, and neutralise antigens from an invading micro-organisms or substances such as a virus, altering it, and so destroying it in the process. As such these proteins have the ability to distinguish between the organism it was synthesised within and an invading organisms and substances.
Yet another group relating to Sensitivity. Some of these proteins are hormones such as insulin/glucagon, ADH, and adrenaline which produce specific effects upon their target organ for example the effect of adrenaline is to increase the efficiency of an animal, such as increased breathing/heartbeat. The release of these hormones is as a result of changes within or outside the body. More directly, proteins are key in the generation and transmission of nerve impulses. Receptor proteins such as rhodopsin which is the photoreceptor protein within rod cells. Rhodopsin is a pigment sensitive to light which in turn stimulates the receptor cells to generate an impulse.
Finally, proteins can act to Control Growth, the most common example of this is thyroxin which controls the growth in young mammals. These proteins control the order of genetic information which is shown within the genome at anyone time, creating a sequential pattern of growth from mitosis.
This essay describes the very generalised functions of different protein of which there are many hundreds resulting from the structures, the combinations of the 20 amino acids alone give a hugely diverse scope for proteins without taking into account the shapes formed. Each has a vary specific function and so can only be loosely grouped into the above.
Bibliography
“Biochemistry” – Stryer
“Biology – A Functional Approach” – M.B.V.Roberts
“Letts A Level Biology” – G.Toole
