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Secondary Structure

Each peptide bond is the result of a condensation reaction where a water molecule is removed from a -COOH and an NH2 group to form a covalent bond.Each peptide bond is therefore a -CONH- group.The partially negative (δ-) oxygen atom of the C=O can form hydrogen bonds with the partially positive (δ+) hydrogen atom of the NH group of a different amino acid.This leads to coiling and folding of the polypeptide.If the hydrogen bonds are formed every 4 amino-acids, a coil called an α-helix is formed.If the hydrogen bonding causes folding, the structure formed is called a β-pleated sheet.

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Specification: AQA Biology (7401), AS-level, 3.1.4.1 General properties of proteins. Topic: Biological Molecules.

Key terms in this lesson

covalent bond
A strong chemical bond formed when a pair of electrons is shared between two atoms.
hydrogen bond
A weak electrostatic attraction between a slightly positive hydrogen atom on one polar molecule and a slightly negative atom, such as oxygen or nitrogen, on another.
condensation reaction
A reaction that joins two molecules together with a covalent bond, with the elimination of a water molecule.

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