7.1.11Human Nutrition
Digestion of Protein — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 5 parts Lesson 8 of 9 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Proteases
Proteases are a group of enzymes that break proteins into amino acids.
Pepsin
- Pepsin This protease is made in the stomach and works best in the acidic conditions found there.
Trypsin
- Trypsin This protease is made in the pancreas and secreted into the duodenum, where it works in alkaline conditions.
Amino acids
- Amino acids The final product of protein digestion is amino acids, which are small and soluble.
Substrate
- Substrate Both enzymes act on protein, which is a long chain of amino acids too large to be absorbed.
Section 2 of 5Where Protein Digestion Happens
Protein digestion takes place in the stomach and the duodenum.
1
Food enters the stomach, where hydrochloric acid gives the low pH at which pepsin works best.
2
Pepsin begins to break the long protein chains into shorter chains of amino acids.
3
The mixture leaves the stomach and enters the duodenum, where the contents become alkaline.
4
Trypsin made in the pancreas acts in the alkaline conditions and continues to break proteins down.
5
Amino acids are absorbed through the lining of the small intestine into the blood.
Section 3 of 5Comparing the Two Enzymes
Comparing the Two Enzymes
Different optimum pH
- Different optimum pH Each enzyme has an optimum pH matched to the part of the gut where it works.
Denaturation
- Denaturation If pepsin is moved into alkaline conditions its shape changes and it stops working.
Specificity
- Specificity Proteases have active sites that fit proteins, so they do not digest starch or fat.
Body temperature
- Body temperature Both enzymes work well at about 37 °C, the normal body temperature.
| Feature | Pepsin | Trypsin |
|---|---|---|
| Made in | Stomach | Pancreas |
| Acts in | Stomach | Duodenum |
| Conditions | Acidic | Alkaline |
| Product | Shorter chains and amino acids | Shorter chains and amino acids |
Section 4 of 5Uses of Amino Acids
Building proteins
- Building proteins Cells join absorbed amino acids together to make new proteins for growth and repair.
Enzymes and hormones
- Enzymes and hormones Many enzymes and hormones are proteins that the body assembles from amino acids.
Not stored
- Not stored The body does not store excess amino acids, so extra amounts are broken down in the liver.
Dietary source
- Dietary source Meat, fish, eggs, pulses and nuts supply the protein that is digested to amino acids.
Section 5 of 5Exam Checklist & Tips
7.1.11 – Key Points for the Exam
- Protease An enzyme that digests protein.
- Pepsin A stomach protease that works in acid conditions.
- Trypsin A pancreatic protease that works in alkaline conditions in the duodenum.
- Amino acid The small soluble unit from which proteins are built.
Common Mistakes
- Saying trypsin works in the stomach; it is secreted into the duodenum and works in alkaline conditions.
- Claiming pepsin works best in alkaline surroundings; its optimum is acidic.
- Writing that proteins are digested into glucose; the products are amino acids.
- Forgetting that trypsin is made in the pancreas, not the small intestine wall.
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