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B1.2.3—Dietary amino acids

Dietary protein supplies essential amino acids that humans cannot synthesize, while non-essential amino acids can be made from other nutrients.

Syllabus
First assessment 2025
Objective
B1.2.3
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper3
Typical marks1–2

Common command terms

  • Outline
  • Define
  • Distinguish
  • State
  • Deduce
  • Evaluate

Scoring notes

Common mistake
Saying non-essential amino acids are not used by the body.

Recent exam appearances

November 2025Paper1A ["HL"] · TZ33[ 1 ]B1.2.3—Dietary amino acids
November 2025Paper2 ["HL"] · TZ12(a)[ 2 ]B1.2.3—Dietary amino acids
November 2019Paper3 ["HL"] · TZ019(b)[ 1 ]B1.2.3—Dietary amino acids
November 2019Paper3 ["HL"] · TZ019(a)[ 1 ]B1.2.3—Dietary amino acids
May 2017Paper3 ["HL"] · TZ118(c)[ 1 ]B1.2.3—Dietary amino acids

Coverage 2016–2025 · Updated 15 Jul 2026

The scarcest amino acid limits protein synthesis

Category Supply to the body
Essential cannot be synthesized in sufficient quantity; must come from food
Non-essential can be produced from other molecules, often by transamination in the liver

Dietary protein → digestion → absorbed amino acids → amino-acid pool → ribosomes. If one required essential amino acid is scarce, it becomes limiting and synthesis of proteins containing it slows even when other amino acids are abundant.

A varied, sufficient plant-based diet can supply all essential amino acids. “Non-essential” means synthesizable, not unimportant.

Checkpoint: build a protein, then identify what can limit it

Shared amino-acid groups condense → peptide bonds build a directional backbone → genetic information specifies residue order → positioned R-groups create folding possibilities.

Limiting change Mechanism Consequence
Essential amino acid unavailable a required monomer is missing synthesis of affected proteins slows
High temperature stabilizing interactions are disrupted conformation and function may be lost
pH away from optimum R-group charges change ionic attractions and H-bond patterns can be disrupted

Dietary amino acids

[ 2 ]

Some of the twenty amino acids that are linked together to make polypeptides in human cells are essential in the diet and others are not. Distinguish between essential and non-essential amino acids.

Concept essentials

  • Essential amino acids must be obtained from the diet.
  • Non-essential amino acids can be synthesized by human cells.
  • A shortage of one essential amino acid can limit protein synthesis.
  • Protein deficiency can cause poor growth, muscle wasting and fluid retention.