CIE AS Biology (9700) 2019-2021 Revision Notes
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2. Biological Molecules
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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
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