B1.2 Proteins
Proteins connect amino acid structure, peptide-bond formation, dietary requirements, folding levels, R-group chemistry, denaturation, and functional protein shapes in cells.
- Syllabus
- First assessment 2025
- Topic
- B1.2
- Level
- SL
Exam analysis
Chance of appearing30%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–2
Most tested objectives
Common question formats
- Definition or recall
- Diagram interpretation
- Process explanation
- Structured response
- Comparison
- Data analysis
Recent exam appearances
November 2025Paper2 ["SL"] · TZ12(a)[ 2 ]B1.2.3—Dietary amino acids
May 2025Paper1A ["SL"] · TZ34[ 1 ]B1.2.3—Dietary amino acids
May 2025Paper1A ["SL"] · TZ23[ 1 ]B1.2.2—Condensation reactions
November 2024Paper1 ["SL"] · TZ29[ 1 ]B1.2.2—Condensation reactions
November 2024Paper1 ["SL"] · TZ19[ 1 ]B1.2.2—Condensation reactions
Practice this topic
Coverage 2010–2025 · Updated 15 Jul 2026
Objective notes
5 learning objectives• Amino acids have an alpha carbon bonded to an amine, carboxyl, hydrogen, and R-group
• The R-group varies between amino acids and determines chemical properties
• Proteins contain C, H, O, N, and usually S
• Condensation joins the carboxyl group of one amino acid to the amine group of another
• A peptide bond forms and water is released
• Chains have an N-terminus and C-terminus and are assembled at ribosomes
• Essential amino acids cannot be synthesized and must be obtained from dietary protein
• Non-essential amino acids can be made by transamination, mainly in the liver
• Deficiency of essential amino acids limits protein synthesis and can cause malnutrition
• Twenty coded amino acids can form vast numbers of sequences
• Protein diversity depends on amino acid type, number, and order
• Genes encode polypeptide sequences; the proteome is the full protein set expressed
• Protein shape determines function, especially enzyme active sites
• High temperature or unsuitable pH disrupts weak bonds and denatures proteins
• Denaturation may be reversible in small proteins but often becomes irreversible