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Haemoglobin is the oxygen carrying pigment found in red blood cells; it is a globular protein, made up of 4 polypeptide chains.

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Introduction

Haemoglobin Haemoglobin is the oxygen carrying pigment found in red blood cells; it is a globular protein, made up of 4 polypeptide chains. Two of these make an identical pair, and are called ? chains. The other two make a different identical pair called ? chains. The four polypeptide chains pack closely together, their hydrophobic R groups pointing in towards the centre of the molecule and their hydrophilic ones pointing outwards. Each ? chain has a tertiary structure very similar to that of myoglobin. The interactions between the hydrophobic R groups inside the molecule are important in holding it in its correct 3-D shape. ...read more.

Middle

So a complete haemoglobin molecule, with four haem groups, can carry four oxygen molecules at a time. It is the haem group which is responsible for the colour of haemoglobin. This colour changes depending on whether or not the iron ions are combined with oxygen. If they are, the molecule is known as oxyhaemoglobin, and is bright red. If not the colour is purplish. Collagen Collagen is a fibrous protein that is found in skin, tendons, cartilage, bones, teeth and the walls of blood vessels. It is an important structural protein, not only in humans, but in almost all animals, and is found in structures ranging from the body wall of sea anemones to the egg cases of dogfish. ...read more.

Conclusion

Any other amino acid would be too large. The three strands are held together by hydrogen bonds. Each complete, three-stranded molecule of collagen interacts with other collagen molecules running parallel to it. Bonds from between the R groups of lysines in molecules lying next to each other. These cross-links hold many collagen molecules side by side, forming fibres. The ends of the parallel molecules are staggered; if they were not, there would be a weak spot running right across the collagen fibre. As it is, collagen has tremendous tensile strength, that is it can withstand large pulling forces. The human Achilles tendon, which is almost all collagen fibres can withstand a huge pulling force, almost one quarter the tensile strength of steel. Paul Barker 12c ...read more.

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