Explain how the structure of collagen and haemoglobin are related to their function.

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Explain how the structure of collagen and haemoglobin are related to their function.

Collagen is a fibrous protein found in skin, tendons, cartilage, bones, teeth and the walls of blood vessels. It has a quaternary structure which is adapted to perform its functions.

Firstly, collagen has great tensile strength. Every third residue of each polypeptide passes through the centre of the triple helix, which is so crowded that only the small R group of glycine (Gly) can fit in. This allows the three helical a-chains to pack tightly together. Furthermore, the triple helix is held together by an extensive network of hydrogen bonds. Covalent cross-links are also present within tropocollagen molecules to impart the collagen fibre with strength and rigidity. Proline with its ring structure also helps in stabilizing the rigid three-stranded collagen helix. Beside, the tropocollagen molecules are arranged in a staggered manner with each other. This confers collagen greater strength.

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Secondly, it is insoluble in water. This is due to the large molecular size of the tropocollagen molecule and the nature of the amino acid residues. Each of the three polypeptide chains in a collagen molecule is about 1000 amino acid residues long and they coil up into a collagen helix. Each polypeptide chain consists of repetitive regular tripeptide sequence of amino acids with an unusually high amount of glycine and praline residues which are hydrophobic in nature.

On the other hand, haemoglobin is a globular protein which is required for the transport of oxygen in blood. It ...

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The candidate explains the scientific structures of the different molecules well. However, the structure whilst being related to the function of tensile strength very well, could also go on to examine the role of collagen and the need for tensile strength in the biology behind tendons and so forth to get a higher grade. I'm not sure how collagen being insoluble in water relates to its function and the candidate should have made the reason clearer in their answer. The biology behind haemoglobin is explained much better and to greater scientific depth. The scientific terms used and the layout of the essay are both to a very high standard.

The response to the question is very well done. The answer is set out in a very clear and concise format, and the level of scientific analysis used is to a very high standard. The candidate clearly sets out the different roles of the two molecules and how they differ from each other for being able to carry out their function.