AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Amino acids have two different functional groups in a molecule.
Full specification wording
Amino acids (HT only): Amino acids have two different functional groups in a molecule.
An amino acid molecule contains two different functional groups: an amine group, –NH₂, and a carboxylic acid group, –COOH.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 2
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
An amino acid molecule contains two different functional groups: an amine group, –NH₂, and a carboxylic acid group, –COOH. Because these groups are different, an amino acid can react with another amino acid in two ways. The amine group of one molecule can react with the carboxylic acid group of another, forming an amide link and releasing water. This allows amino acids to join into chains called polypeptides or proteins. The presence of two different functional groups, rather than two identical ones, means a single type of amino acid can polymerise with itself, and different amino acids can also combine in any order.
What earns the marks
- An amino acid contains an amine group, –NH₂.
- An amino acid contains a carboxylic acid group, –COOH.
- The two functional groups are different from each other.
- The amine group of one amino acid reacts with the carboxylic acid group of another.
- An amide link forms and water is eliminated.
- Amino acids can join to form polypeptides or proteins.
Common mistakes and how to put them right
Stating that amino acids contain two identical functional groups.
Put it right by naming the amine and carboxylic acid groups as different.
Confusing the amine group with the amide link.
Put it right by noting that the amine group is a reactant and the amide link is the bond formed.
Forgetting that water is eliminated when amino acids join.
Put it right by linking amide formation to condensation.
Exam tips
- Name both functional groups precisely: amine and carboxylic acid.
- Show the amide link and the eliminated water when explaining polymerisation.
- Use the term polypeptide or protein for the polymer formed from amino acids.
Try the lesson
The start of the Amino acids (HT only): Amino acids have two different functional groups in a molecule. lesson, made from checked teaching notes for this specification point.
Have a go first
Which two different functional groups are present in a molecule of an amino acid?
Listen
An amino acid molecule contains two different functional groups: an amine group, –NH₂, and a carboxylic acid group, –COOH. Because these groups are different, an amino acid can react with another amino acid in two ways. The amine group of one molecule can react with the carboxylic acid group of another, forming an amide link and releasing water. This allows amino acids to join into chains called polypeptides or proteins. The presence of two different functional groups, rather than two identical ones, means a single type of amino acid can polymerise with itself, and different amino acids can also combine in any order. A strong answer earns marks for these points. An amino acid contains an amine group, –NH₂. An amino acid contains a carboxylic acid group, –COOH. The two functional groups are different from each other. The amine group of one amino acid reacts with the carboxylic acid group of another. A common slip: Stating that amino acids contain two identical functional groups. Instead, naming the amine and carboxylic acid groups as different. Exam tip: Name both functional groups precisely: amine and carboxylic acid.
Key words
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Amine groups
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Carboxylic acid groups
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Amide links
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See every definition
- Amine groups
- A functional group, –NH₂, contained in an amino acid molecule.
- Carboxylic acid groups
- A functional group, –COOH, contained in an amino acid molecule.
- Amide links
- The link formed when the amine group of one amino acid reacts with the carboxylic acid group of another, releasing water.
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