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CIE AS Biology (9700) 2019-2021 Revision Notes

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2. Biological Molecules

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Page 45

The generalised structure of an amino acid

Peptide bond

In order to form a peptide bond a hydroxyl (-OH) is lost from a carboxylic group of one

amino acid and a hydrogen atom is lost from an amine group of another amino acid

The remaining carbon atom (with the double-bonded oxygen) from the first amino acid bonds

to the nitrogen atom of the second amino acid

This is a condensation reaction so water is released. The resulting molecule is a dipeptide

When many amino acids are bonded together by peptide bonds the molecule formed is called

a polypeptide. A protein may have only one polypeptide chain or it may have multiple

chains interacting with each other

During hydrolysis reactions polypeptides are broken down to amino acids when the addition

of water breaks the peptide bonds

Amino acids are bonded together by covalent peptide bonds to form a dipeptide in a