Compare pepsin and trypsin environments
Connect protease source, action site and pH.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall large and small nutrient molecules, cell membranes and enzyme specificity.
- Use the stated diagram keys and evidence; models are not to scale.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which is a protease?
What you will learn
- Connect protease source, action site and pH.
- Distinguish overall amino-acid production from individual protease steps.
Pepsin acts in the stomach
Pepsin is a gastric protease acting on protein in acidic stomach conditions. Gastric acid supports its suitable environment. The overall protease pathway ultimately produces amino acids, but pepsin can first make shorter peptide fragments.
Do not place pepsin’s principal action in the alkaline small intestine or call hydrochloric acid the enzyme itself. A named enzyme’s action site and pH should agree.
Trypsin acts in the small intestine
Trypsin is a protease supplied by the pancreas and acts on protein in alkaline conditions in the small intestine. It can also produce peptide fragments before later steps complete amino-acid production.
The pancreas secretes the inactive precursor in detailed physiology, activated in the intestinal pathway; the syllabus focuses on trypsin’s digestive action and environment. The school map does not imply active protease safely digests the pancreas itself.
Sources for this lesson
Pause and explain
Which comparison is correct?
Worked example
Complete the comparison: pepsin—stomach—acidic; trypsin—___—___.
Show the worked solution
- Trypsin acts in small intestine.
- Suitable conditions are alkaline.
- Its pancreatic source is separate from action site.
Answer Trypsin: small intestine, alkaline conditions; supplied by the pancreas.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State the action region and conditions for pepsin and trypsin.
Give me a hint
Pair enzyme, region and pH.
Compare my reasoning
- Pepsin: stomach, acidic.
- Trypsin: small intestine, alkaline.
Pepsin acts in acidic stomach conditions; trypsin in alkaline small-intestine conditions.
Look for these in your work
- Both pairs.
- No source/action swap.
Why is “pancreas” an incomplete answer for trypsin’s action region?
Give me a hint
Pancreas is the source in the school map.
Compare my reasoning
- Pancreatic secretion reaches small intestine.
- Trypsin acts on food there.
The pancreas supplies it, but its required action region is the small intestine.
Look for these in your work
- Correct source.
- Correct action site.
A supplied pepsin test works poorly after alkalinisation. Does this show trypsin must also work poorly in alkaline conditions?
Give me a hint
Enzyme environments differ.
Compare my reasoning
- The observation concerns pepsin.
- Trypsin’s suitable environment is alkaline.
- Use its own controlled evidence.
No; pepsin’s response does not establish trypsin’s response.
Look for these in your work
- Enzyme specificity of conditions.
- No universal inference.
Common mistakes
- Source organ and action region differ for trypsin.
- Do not claim each protease alone instantly releases all final amino acids.
What can you explain now?
Which comparison is correct?
Compare with the explanation
Pepsin: acidic stomach; trypsin: alkaline small intestine.
The named environments differ.
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Make it stick
Compare source, action region and environment for both proteases.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.