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Definition
| This is the most basic level of protein folding, and consists of a few basic motifs that are found in all proteins. It's held together by hydrogen bonds between the carboxyl groups and the amino groups in the polypeptide backbone. The two most common structure motifs are the a-helix and the b-sheet. |
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| This is just the sequence of amino acids in the polypeptide chain, so is not really a structure at all. However,it does determine the rest of the protein structure |
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Definition
| The polypeptide chain is wound round. It is held together by hydrogen bonds running parallel with the long helical axis. There are so many hydrogen bonds that this is a very stable and strong structure. |
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| The polypeptide chain zig-zags back and forward forming a sheet of antiparallel strands. Once again it is held together by hydrogen bonds |
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Definition
This is the compact globular structure formed by the folding up of a whole polypeptide chain. Every protein has a unique structure, which is responsible for its properties and function. For example the shape of the active site in an enzyme is due to thid structure. It is held together by bonds between the R groups of the amino acids in the protein, and so depends on what the sequence of amino acids is. There are three kinds of bonds involved:hydrogen bonds, which are weak.
ionic bonds between R-groups with positive or negative charges, which are quite strong.
sulphur bridges - covalent S-S bonds between two cysteine amino acids, which are strong |
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Definition
| This structure is found in proteins containing more than one polypeptide chain, and simply means how the different polypeptide chains are arranged together. The individual polypeptide chains are usually globular, but can arrange themselves into a variety of shapes. |
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