C1.1.4—Enzymes as globular proteins
Enzymes are usually globular proteins whose folded active-site pockets bind substrates and catalyse specific reactions in living cells during catalysis.
- Syllabus
- First assessment 2025
- Objective
- C1.1.4
- Level
- SL
Exam analysis
Chance of appearing1%of analysed past papers
Latest appearanceMay 2021
Most common paperPaper1
Typical marks1
Common command terms
- Define
- State
Recent exam appearances
May 2021Paper2 ["SL"] · TZ23(b)[ 1 ]C1.1.4—Enzymes as globular proteins
May 2013Paper1 ["SL"] · TZ210[ 1 ]C1.1.4—Enzymes as globular proteins
Practice this objective
Coverage 2013–2021 · Updated 15 Jul 2026
Globular Protein Shape Creates an Active Site
Most enzymes are globular proteins whose folded three-dimensional shape creates a specific active site.
Hydrophobic interactions, hydrogen bonds, ionic attractions and disulfide bonds stabilize the fold. The active site presents chemical groups in a geometry that binds substrates and promotes the transition state.
Connect structure to function:
- amino-acid sequence
- folding and active-site shape
- substrate binding
- catalytic chemistry
Changing one amino acid near an active site can alter its shape and reduce activity even if the rest of the protein remains folded.
An enzyme’s function depends on its three-dimensional conformation, not only its amino-acid list.
Enzymes as globular proteins
Assessment in practice
1 marksHow it is assessed
This objective is assessed through structured response, commonly using Define / State.
Command terms
Define / State
What earns marks
Build the answer around this relationship: Most enzymes are globular proteins with specific folded shapes.
Representative question
Question 1
State a role of the active site of an enzyme.
Enzyme Catalysis and Rate
Enzymes are biological catalysts that lower activation energy and remain unchanged. Their globular protein shape creates active-site specificity; induced fit aligns substrates; molecular motion and collisions affect rate; temperature, pH, and substrate concentration change activity; assays measure substrate loss or product formation over time.
- Define enzyme as biological catalyst, effective in small amounts and unchanged.
- Use active site, specificity, induced fit, ES complex, and activation energy in mechanism answers.
- Use curve shapes: temperature optimum/denaturation, pH optimum, and substrate saturation plateau.
- For practicals, state what is measured per unit time and use initial rate, controls, and replicates.
Concept essentials
- Most enzymes are globular proteins with specific folded shapes.
- The active site is the enzyme region where substrate binds.
- Amino acid sequence contributes to enzyme structure.
- Substrate specificity follows from active-site shape and chemistry.