B1.2.5—Effect of pH and temperature
Protein function depends on shape, so high temperature or unsuitable pH can denature proteins by disrupting stabilizing bonds and active sites.
- Syllabus
- First assessment 2025
- Objective
- B1.2.5
- Level
- SL
Exam analysis
Chance of appearing2%of analysed past papers
Latest appearanceMay 2022
Most common paperPaper1
Typical marks1–2
Common command terms
- Outline
- Explain
- Identify
Scoring notes
- Common mistake
- Claiming denaturation changes the amino-acid sequence.
Recent exam appearances
May 2022Paper2 ["SL"] · TZ12(c)[ 2 ]B1.2.5—Effect of pH and temperature
May 2022Paper2 ["SL"] · TZ12(b)[ 1 ]B1.2.5—Effect of pH and temperature
May 2016Paper1 ["SL"] · TZ03[ 1 ]B1.2.5—Effect of pH and temperature
May 2011Paper1 ["SL"] · TZ111[ 1 ]B1.2.5—Effect of pH and temperature
Practice this objective
Coverage 2011–2022 · Updated 15 Jul 2026
Protein Shape Depends on Conditions
Protein shape is maintained by weak interactions that can be disrupted by extreme pH or temperature, causing denaturation and loss of function.
Heating increases molecular motion and extreme pH changes charges on R-groups. These changes disturb hydrogen bonds, ionic attractions and other interactions holding the folded chain in its working shape.
Predict a condition effect by asking:
- which interaction is disturbed
- whether the chain unfolds or changes active-site shape
- whether the change is reversible under the conditions
An enzyme may work faster as temperature rises to its optimum, then lose activity sharply when heating disrupts the shape of its active site.
Denaturation changes conformation, not necessarily the amino-acid sequence. Do not treat every loss of activity as peptide-bond hydrolysis.
Effect of pH and temperature
Assessment in practice
1–2 marksHow it is assessed
This objective is assessed through structured response, commonly using Outline / Explain / Identify.
Command terms
Outline / Explain / Identify
What earns marks
Build the answer around this relationship: Denaturation changes protein conformation and can remove biological function.
Watch for
Claiming denaturation changes the amino-acid sequence.
Representative question
Question 1
Outline the process of protein denaturation.
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
- Denaturation changes protein conformation and can remove biological function.
- High temperature and unsuitable pH can disrupt bonds within proteins.
- Enzyme denaturation changes the active site and reduces substrate binding.
- Denaturation usually leaves the primary amino-acid sequence unchanged.