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α-helix

β-pleated sheet

The α-helix shape occurs when the hydrogen bonds form between every fourth peptide

bond (between the oxygen of the carboxyl group and the hydrogen of the amine group)

The β-pleated sheet shape forms when the protein folds so that two parts of the

polypeptide chain are parallel to each other enabling hydrogen bonds to form between

parallel peptide bonds

Most fibrous proteins have secondary structures (e.g. collagen and keratin)

The secondary structure only relates to hydrogen bonds forming between the amino

group and the carboxyl group (the ‘protein backbone’)

The hydrogen bonds can be broken by high temperatures and pH changes

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CIE AS Biology (9700) 2019-2021 Revision Notes

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2. Biological Molecules

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