A-Level Chemistry: Amino Acids, Proteins and DNA
This page summarises the main syllabus ideas typically covered in the Amino Acids,
Proteins and DNA section of A-level Chemistry.
Core syllabus summary:
structure and properties of amino acids, zwitterions and acid-base behaviour,
peptide bond formation by condensation, hydrolysis of peptides and proteins,
protein structure and bonding, chromatography of amino acids, and DNA structure
and bonding.
1) Amino acids
- Know the general structure of an α-amino acid.
- Understand that amino acids contain both an amine group and a carboxylic acid group.
- Explain why amino acids can behave as both acids and bases.
- Understand the formation of zwitterions.
- On some exam boards, draw the forms present in acidic and alkaline solution.
- Some specifications also include chirality and optical activity of 2-amino acids.
2) Peptide bonds and proteins
- Understand that amino acids join by condensation reactions.
- Know that this forms peptide (amide) bonds.
- Describe the formation of dipeptides, polypeptides, and proteins.
- Be able to draw peptide structures where required.
- Understand that hydrolysis breaks peptide bonds and reforms the constituent amino acids.
3) Protein structure
- Learn the meanings of primary, secondary, and tertiary structure.
- Understand that protein shape depends on the sequence of amino acids.
- Explain how hydrogen bonding helps stabilise structure.
- Some boards also require knowledge of disulfide (S–S) bonds.
4) Enzymes
- Know that enzymes are proteins and act as biological catalysts.
- Understand the idea of a specific active site.
- Some boards include enzyme inhibition and stereospecific active sites.
5) Chromatography of amino acids
- Know that amino acids can be separated by chromatography.
- AQA specifies thin-layer chromatography and
Rf values.
- OCR B mentions paper chromatography and locating agents such as ninhydrin.
- Edexcel also links amino-acid separation to chromatography.
6) DNA
- Some boards include DNA in detail, while others focus more on amino acids and proteins.
- Learn that DNA is built from nucleotides.
- Each nucleotide contains a phosphate, a sugar, and a base.
- Understand the sugar-phosphate backbone.
- Know that DNA consists of two complementary strands in a double helix.
- Explain the role of hydrogen bonding in base pairing.
7) Exam board differences
- AQA: includes amino acids, proteins, enzymes, DNA structure, and cisplatin binding to DNA.
- OCR Chemistry B (Salters): includes amino acids, protein structure, enzymes, DNA as a condensation polymer, base pairing, and how DNA encodes amino acid sequences.
- OCR Chemistry A: focuses more on amino acids and proteins, with a DNA-related point through cis-platin binding to DNA.
- Edexcel: mainly focuses on amino acids and proteins; DNA is less prominent in this topic.