IB Biology HL B1.2 Proteins Questions

Practise IB Biology HL B1.2 with questions that move from amino-acid and peptide-bond diagrams to protein folding, interactions, denaturation and structure–function reasoning.

90 questions in this syllabus scope, with question parts counted together.

Exam analysis

HL · 2010–2025

Papers with this topic35 / 117in the analysed sample

Latest appearanceNovember 2025

Tagged question parts48

Paper types5

Most tested objectives

B1.2.2—Condensation reactions7 papers
B1.2.3—Dietary amino acids6 papers
B1.2.8 (HL)—Secondary structure6 papers
B1.2.9 (HL)—Tertiary structure5 papers
B1.2.1—Generalized amino acid structure4 papers

Common question formats

Definition or recall
Diagram interpretation
Process explanation
Structured response
Comparison
Data analysis

Recent exam appearances

November 2025Paper 2 HL · TZ1Q2(a), 2(b), 2(c)[ 7 ]

November 2025Paper 1A HL · TZ3Q3[ 1 ]

May 2025Paper 2 HL · TZ1Q2(a), 2(b), 2(c)(i)[ 5 ]

117 papers analysed · Tagging incomplete

Exam points

Identify an amino acid’s alpha carbon and its amine group, carboxyl group, hydrogen and variable R-group, and relate protein composition to C, H, O, N and usually S.
Classify R-groups as acidic, basic, polar hydrophilic or non-polar hydrophobic, and explain how their chemistry affects solubility, interactions, folding and function.
Explain amino-acid condensation: peptide-bond formation, water release, dipeptide or polypeptide products, N- and C-termini, and ribosomal chain assembly.
Distinguish essential amino acids that must come from dietary protein from non-essential amino acids made by the body, and explain deficiency, limiting amino acids and protein malnutrition.
Relate amino-acid type, number and order, genes, codons and translation to primary structure and the diversity of polypeptide sequences and protein functions.
Explain how high temperature, extreme pH, salts or heavy metals denature proteins by disrupting weak interactions, changing active sites and reducing biological activity.
Identify alpha helices and beta-pleated sheets as secondary structures stabilized by regular hydrogen bonds between peptide-group C=O and N-H atoms.
Define tertiary structure as the three-dimensional folding of one polypeptide and identify hydrogen-bond, ionic, disulfide-covalent and hydrophobic interactions between R-groups.
Define quaternary structure as two or more polypeptide chains forming one functional protein, using haemoglobin or insulin as examples.
Distinguish compact, often soluble globular proteins from long, often insoluble fibrous proteins and relate each form to catalysis, transport, signalling or structural strength.

Covered syllabus points

B1.2.1—Generalized amino acid structure B1.2.2—Condensation reactions B1.2.3—Dietary amino acids B1.2.4—Infinite variety of peptide chains B1.2.5—Effect of pH and temperature B1.2.6 (HL)—Chemical diversity in R-groups B1.2.7 (HL)—Primary structure impact B1.2.8 (HL)—Secondary structure B1.2.9 (HL)—Tertiary structure B1.2.10 (HL)—Effect of polar/non-polar amino acids B1.2.11 (HL)—Quaternary structure B1.2.12 (HL)—Globular vs. fibrous proteins

Exam points

Draw the general amino acid structure with an alpha carbon bonded to amine, carboxyl, H and R-group.
State that proteins contain carbon, hydrogen, oxygen and nitrogen, and usually sulfur.

[Maximum number: 1]

The diagram shows the structure of the protein CXCL12.

Which chemical group is found at X ?

$\mathrm{NH}_{2}$

NOH

COH

COOH

Exam points

Mark the peptide bond between C=O and N-H groups in a dipeptide or polypeptide diagram.
Show condensation between amino acids, with peptide-bond formation and water release.
Calculate peptide bonds from amino-acid totals and the number of separate polypeptide chains.
Identify ribosomes as the site where amino acids are joined into polypeptide chains.

[Maximum number: 1]

The figure shows a tripeptide.

Label one peptide bond in this molecule.

Exam points

Distinguish essential amino acids obtained from food from non-essential amino acids made from other amino acids.
Compare essential amino-acid data across foods or diets to judge which source better meets dietary needs.
Use an amino-acid table to identify which amino acids must be supplied in the diet.
Explain protein-deficiency effects such as reduced growth, muscle wasting and malnutrition.

[Maximum number: 1]

The table shows some essential and non-essential amino acids.

What is a valid conclusion for an amino acid in the table?

Lysine is synthesized by the human body.

Alanine can only be obtained from food.

Glycine is not used in the human body.

Valine must be supplied in the diet.

Exam points

Explain how 20 amino acids in different numbers and orders produce many possible polypeptide sequences.
Relate gene base sequence to its encoded amino-acid sequence and the resulting polypeptide or enzyme.

[Maximum number: 7]

Proteins are an extraordinarily diverse group of carbon compounds that have a wide range of roles in cells.

Describe the structure of proteins, including features that are common to all proteins and features that vary.

a. composed of one or more polypeptides / some are single polypeptides others made of 2 or more polypeptide chains / all proteins consist of, at least, one polypeptide chain;

b. a polypeptide/protein is a chain of amino acids;

c. (chains of) amino acids linked by peptide bonds;

d. twenty different amino acids/ amino acids have different R groups/ R groups can be hydrophilic/polar or hydrophobic/non-polar;

e. primary structure is the sequence/order (and number) of amino acids in the polypeptide;

f. any sequence/order of amino acids could be linked together hence many possible polypeptides/proteins;

g. secondary structure is the formation of alpha/ $\alpha$ helices and beta/ $\beta$ pleated sheets;

h. secondary structure stabilized by hydrogen bonding;

i. tertiary structure is the further folding of the polypeptide / tertiary structure is the threedimensional (3-D) conformation/structure/shape of a protein;

j. tertiary structure stabilized by interactions / ionic bonds/hydrogen bonds/disulfide bridges between R groups;

k. fibrous or globular are the two main classes of conformation/three-dimensional/ 3-D structure/shape;

l. conformation/three-dimensional (3-D) structure determined by amino acid sequence;

m. quaternary structure if two or more polypeptides are linked to form a (single) protein OR quaternary structure if a prosthetic group is linked (to form a conjugated protein);

Marking guidance:

Accept clearly annotated diagrams.

Mpc: accept a clearly annotated diagram of the bond between 2 drawn amino acids.

Exam points

Explain how high temperature or extreme pH disrupts protein bonds, changes shape and can impair function.
Interpret temperature graphs showing falling alpha-helix content as evidence of protein denaturation.

[Maximum number: 1]

Scientists have heated a solution containing the protein albumin and measured its relative alpha helix content, shown on the graph.

What does the zone labelled X indicate?

Rapid increase in beta pleated sheets

Rapid formation of hydrogen bonds

Rapid increase in denatured protein molecules

Rapid decrease in peptide bonds

Exam points

Distinguish hydrophobic/non-polar from hydrophilic/polar R-groups in amino-acid questions.
Relate R-group properties to interactions that shape protein folding and form.

[Maximum number: 2]

Describe how the diversity of amino acids gives proteins a broad range of forms.

Exam points

Define primary structure as the ordered sequence and number of amino acids joined by peptide bonds in a polypeptide chain.
Relate DNA genetic information to the amino-acid sequence that determines a protein’s primary structure.

[Maximum number: 1]

The image shows the structure of hemoglobin.

What determines the primary structure of hemoglobin?

Genetic information

Hydrogen bonding

Four polypeptide chains

Side chain interactions

Exam points

Identify alpha helices and beta-pleated sheets as local secondary structures in polypeptides.
Explain that regular hydrogen bonds between peptide-group C=O and N-H atoms stabilize secondary structure.
Distinguish secondary-structure hydrogen bonding from tertiary interactions when interpreting protein diagrams or models.

[Maximum number: 1]

The diagram shows a section through the melatonin receptor, with melatonin attached to its binding site. Darker grey areas show the surface of the protein and paler areas are internal. The membrane in which this receptor is located is also shown.

The receptor contains seven alpha helices and one other secondary structure. Deduce what this other secondary structure is.

Exam points

Define tertiary structure as the unique three-dimensional conformation formed by folding one polypeptide chain.
Identify hydrogen-bond, ionic, disulfide-covalent and hydrophobic interactions between R-groups that stabilize tertiary structure.

[Maximum number: 1]

Which row correctly matches the level of structure of a protein molecule with the bonds that stabilize it?

Level of structure

Bonds

primary

peptide and hydrogen bonds between amine and
carboxyl groups

secondary

hydrogen bonds between R-groups of amino acids

tertiary

disulfide, hydrogen and ionic bonds between R-groups
of amino acids

quaternary

covalent bonds between hydrophobic and hydrophilic
regions on the polypeptide subunits

Exam points

Distinguish polar/hydrophilic from non-polar/hydrophobic amino-acid R-groups.
Explain hydrophobic-core and polar-surface positions in soluble globular proteins.
Relate membrane-protein residue polarity to water-facing regions and lipid tails.

[Maximum number: 2]

Discuss briefly whether amino acids on the surface of the protein are likely to be polar or non-polar.

Exam points

Classify a protein with multiple associated polypeptide chains as quaternary structure.
Identify haemoglobin’s alpha/beta subunits and attached haem groups in a protein model.
Use insulin diagrams to identify two polypeptide chains linked by disulfide bridges.

[Maximum number: 1]

This diagram shows the amino acids present in a molecule of insulin, using three-letter abbreviations.

What describes the structure of insulin?

Insulin is a fibrous protein, since the amino acids are arranged in a linear pattern.

Insulin consists of a single continuous polypeptide chain with one free amino terminal and one free acid terminal.

Insulin has three disulphide bridges giving it tertiary structure and two polypeptide chains giving it quaternary structure.

Insulin has primary and secondary structure only, as there is no evidence of a three-dimensional shape in the diagram.

Exam points

Compare compact, often soluble globular proteins with long, often insoluble fibrous proteins.
Match protein form to roles such as collagen support, silk tensile strength or insulin regulation.
Classify globular and fibrous forms from protein-structure diagrams.

[Maximum number: 1]

Which protein is identified with its function?

Protein

Function

collagen

provides strength and support for tissues and organs

rhodopsin

enzyme found in tears

insulin

raises blood glucose concentrations

immunoglobulin

helps in blood clotting

[Maximum number: 3]

The figure shows a tripeptide.

(a)

Label one peptide bond in this molecule.

[ 1 ]

(b)

Describe the secondary structure of proteins.

[ 2 ]

a polypeptide wound into a helical structure / alpha/ɑ helix

OR

polypeptide folded back on itself forming a pleated sheet / beta/ $\beta$ pleated sheet;

b stabilized/held in shape by/due to hydrogen bonds (between C=O and N-H groups);

c secondary structures are regular/unvarying (within polypeptides/proteins);

Marking guidance:

Allow annotated diagrams

2 max

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Exam analysis

Most tested objectives

Common question formats

Recent exam appearances

Covered syllabus points

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