structural differences between fibrous and globular proteins.

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Question: Explain with examples, the structural differences between fibrous and globular proteins.

A globular protein has a fixed specific sequence of amino acids that are non-repetitive while a fibrous protein has a repetitive regular sequence of amino acid. For example, haemoglobin, a globular protein is made up of 4 polypeptide chains to form a tetramer (α2β2), composed of two identical alpha-beta (αβ) dimers. Collagen, a fibrous protein, has a primary structure characterized by a repeating tripeptide sequence of Glycine – X – Y. (X is proline, Y is either hydroxyproline or hydroxylysine)  

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A globular protein has a more compact structure owing to highly contorted pattern of folding, bending and twisting along polypeptide chain to give the protein a spherical 3D shape while a fibrous protein is usually formed with elongated polypeptide chains wrapped around to form multi-molecular paralleled filaments to strands. For example, haemoglobin is a tetramer made up of 4 polypeptide chains of 2α chains and 2β chains. These four subunits are packed to form an overall spherically shaped molecule. However, collagen, a fibrous protein, is formed with three polypeptide chains lie parallel and wind round one another, forming a tropocollagen. The ...

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Grammar, spelling and punctuation are all correct.

The analysis of the proteins is quite deep, but to improve their grade the candidate could have presented the information in a tabular format which would have made the information easier to read and mark. The candidate could have used more example to explain the differences between the two different proteins, for example going beyond the question and relating the structural differences to how the protein actually functions. Scientific terms used show a high level of understanding.

Good overall response to the question. The answer is rather short but provides a perfect example of what an A level candidate should be aiming for in terms of length and segregation of the different parts, going for comparison rather than describing each protein separately which is good in this instance. The response to the question is clear and concise.