B1.2.4—Infinite variety of peptide chains
Protein diversity arises because amino acids can be linked in enormous numbers of different orders and chain lengths through translation.
- Syllabus
- First assessment 2025
- Objective
- B1.2.4
- Level
- SL
Exam analysis
Chance of appearing1%of analysed past papers
Latest appearanceMay 2021
Most common paperPaper2
Typical marks7
Common command terms
- Explain
- Describe
Recent exam appearances
May 2021Paper2 ["SL"] · TZ16(b)[ 7 ]B1.2.4—Infinite variety of peptide chains
Practice this objective
Coverage 2021–2021 · Updated 15 Jul 2026
Sequence Creates Protein Variety
The genetic code specifies 20 common amino acids, and peptide chains can contain from a few to thousands of residues in any order, creating an immense variety of possible sequences.
At each position there can be many amino-acid choices, so the number of possible sequences grows exponentially with chain length. Genes specify particular orders; different cells express different sets of proteins, forming their proteomes.
Protein variety depends on amino-acid type, number and order. Sequence positions place different R-group chemistries together during folding, helping determine the final three-dimensional form and function.
Two chains with the same numbers of alanine and glycine can have different primary structures—and potentially different folds—when those residues occur in different orders.
A possible sequence is not automatically a stable functional protein, and a sequence change matters only through its effect on folding, stability, interactions or a functional site.
Infinite variety of peptide chains
Assessment in practice
2–7 marksHow it is assessed
This objective is assessed through structured response, commonly using Explain / Describe.
Command terms
Explain / Describe
What earns marks
Build the answer around this relationship: Protein primary structure depends on amino-acid number, type and order.
Representative question
Question 1
Cells produce a large variety of proteins with different sequences of amino acids. Explain how this is done.
Build And Use Proteins
The core protein story is build -> vary -> function. Amino acids share a backbone but differ in R-groups. Peptide bonds form by condensation between carboxyl and amine groups. Some amino acids must come from diet, or protein synthesis is limited. Twenty coded amino acids create many sequences by type, number, and order. Finally, shape determines function, so denaturation changes performance.
- Amino acids share an alpha-carbon backbone and vary in R-groups.
- Peptide bonds form by condensation and release water.
- Essential amino acids must be obtained from dietary protein.
- Protein diversity depends on amino acid type, number, and order.
- Protein shape determines function; denaturation changes shape and function.
Concept essentials
- Protein primary structure depends on amino-acid number, type and order.
- Genes encode polypeptide sequences through transcription and translation.
- Different R-groups give amino acids different chemical properties.
- Many possible amino-acid sequences create a huge variety of proteins.