GCSE Chemistry revision

Amino acids

Synthetic and naturally occurring polymers (chemistry only)

AQA 4.7.3.3 Higher Tier only

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Amino acids contain two key functional groups: a carboxyl (carboxylic acid) group and an amino group, both attached to a central carbon atom.
Each amino acid also contains an R group, which varies between different amino acids and gives each one its unique identity.
The name 'amino acid' is a helpful reminder that the molecule contains both an amino group and a carboxylic acid group.

1. Amino Acids: The Monomers of Polypeptides AQA

Amino acids contain two key functional groups: a carboxyl (carboxylic acid) group and an amino group, both attached to a central carbon atom.
Each amino acid also contains an R group, which varies between different amino acids and gives each one its unique identity.
The name 'amino acid' is a helpful reminder that the molecule contains both an amino group and a carboxylic acid group.

Adjacent amino acids join together through condensation reactions, where the –OH from the carboxyl group and the –H from the amino group are removed to form water (H₂O).
The bond formed between two amino acids is called an amide bond, amide link, or peptide bond — all three names refer to the same bond.
The general equation for polymerisation shows the amino acid monomer forming a repeating unit in brackets, with n placed before the monomer and before the H₂O produced.

2. Condensation Reactions & Peptide Bond Formation AQA

Adjacent amino acids join together through condensation reactions, where the –OH from the carboxyl group and the –H from the amino group are removed to form water (H₂O).
The bond formed between two amino acids is called an amide bond, amide link, or peptide bond — all three names refer to the same bond.
The general equation for polymerisation shows the amino acid monomer forming a repeating unit in brackets, with n placed before the monomer and before the H₂O produced.

A polypeptide is formed when many amino acids are joined together in a long chain via peptide bonds.
When a polypeptide folds or combines with other polypeptides, the resulting structure is called a protein.
Because there are many different amino acids that can combine in countless sequences, a huge variety of proteins with different functions can be produced.
Proteins carry out a wide range of functions in the body, including catalysing chemical reactions as enzymes and providing structural support to tissues.

3. Polypeptides & Proteins AQA

A polypeptide is formed when many amino acids are joined together in a long chain via peptide bonds.
When a polypeptide folds or combines with other polypeptides, the resulting structure is called a protein.
Because there are many different amino acids that can combine in countless sequences, a huge variety of proteins with different functions can be produced.
Proteins carry out a wide range of functions in the body, including catalysing chemical reactions as enzymes and providing structural support to tissues.