The Function of Proteins Are Linked to Their Shape

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The functions of protein are linked to their shape

Proteins are polymers of amino acids joined by strong peptide bonds. The combination of any of the twenty amino acids in any length and sequence allows an almost infinite number of possible structures and functions.

The sequence of amino acids in the polypeptide chain is termed the primary structure. The primary structure is unique to a given protein. The primary structure can fold regularly to form either an α-helix or β-pleated sheet. The secondary structure is held together by hydrogen bonds between adjacent peptide bonds. The primary structure can further fold in an irregular but not random manner to form an overall three dimensional shape that more specifically determines the biological functions of the individual protein. This 3D structure is held together by bonds formed between the R-groups of amino acids.

For movement, animals use muscle contraction. Muscle fibres are composed of two protein filaments, myosin which is a thick filament and actin which is thinner. Actomyosin cross-bridges can form between the two which move relative to one another on hydrolysis of ATP drawing actin into myosin. This sliding filament theory shows how a sarcomere contracts. This contraction is used in a variety of applications including constriction or dilation of blood vessel to modify blood flow through tissues, pupil diameter to control light entry into eyes or the generation of a force at a joint to move a hand away from a hot object.

Some proteins adopt a structural role. For example, keratin, a protein in skin, is formed from coils that twist together to form rope-like structures that are both flexible and strong. This strength is utilised in animals as claws or horns for predation or protection, or hair as camouflage or insulation. Collagen, another important structural protein that comprises connective tissue…...

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