Explain the overall protease pathway
Connect protein digestion to amino acids without skipping intermediate steps.
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and 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
What are protein building blocks?
What you will learn
- Connect protein digestion to amino acids without skipping intermediate steps.
- Distinguish digestive breakdown from cellular protein synthesis.
Protein supplies amino-acid products
Proteases catalyse protein breakdown. Across the overall digestive pathway, proteins are broken down to amino acids that can be absorbed and used by cells. Individual proteases may first make shorter peptide fragments rather than each releasing all final amino acids directly.
For the Core summary, state protein → amino acids by proteases. Keep this overall outcome separate from the detailed actions of named enzymes in the Extended lessons.
Separate digestion and protein synthesis
Protein breakdown occurs in the digestive system. Amino acids are absorbed and later used by cells to synthesise their own proteins. This rebuilding is assimilation, not the reversal of digestion inside the stomach.
A protein food contains several components. Finding reducing sugar after a mixed-food treatment does not by itself show that protein became glucose; choose a suitable measure for the pathway being tested.
Sources for this lesson
Pause and explain
Which description avoids overstating a single enzyme step?
Worked example
A table says protease converts all protein into fatty acids. Correct the overall pathway.
Show the worked solution
- Identify protein substrate.
- Name amino-acid final products.
- Keep lipase products separate.
Answer Proteases contribute to overall protein digestion to amino acids.
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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 Core substrate, enzyme group and final product for protein digestion.
Give me a hint
Use the overall pathway.
Compare my reasoning
- Protein.
- Proteases.
- Amino acids.
Proteins are digested by proteases to amino acids across the overall pathway.
Look for these in your work
- All three roles.
- Overall-product wording.
Why is making body protein from absorbed amino acids assimilation rather than digestive protease action?
Give me a hint
One builds a cellular product; one breaks dietary molecules.
Compare my reasoning
- Digestion breaks dietary protein down.
- Cells use amino acids to build required protein.
Cellular uptake/use and protein synthesis is assimilation, following digestion and absorption.
Look for these in your work
- Direction distinction.
- Correct process.
A mixed meal produces reducing sugars after treatment. Can that alone prove the proteins were digested into amino acids?
Give me a hint
The measured product is from another nutrient category.
Compare my reasoning
- Sugars can arise from carbohydrate.
- A protein-pathway product needs appropriate evidence.
No; the sugar test does not establish amino-acid production from protein.
Look for these in your work
- Measurement mismatch.
- Limit the inference.
Common mistakes
- Do not substitute lipid products for protein products.
- A named protease may first produce shorter peptides.
What can you explain now?
Which description avoids overstating a single enzyme step?
Compare with the explanation
The overall protease pathway produces amino acids, sometimes through shorter peptides.
This distinguishes pathway and individual step.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Separate the overall digestion outcome from individual peptide-making steps.
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.