Enzymes
Senior 2 · Biology
Enzymes
Lesson 4 of 4
16 min
Let's begin
Every stage of making ikigage, the traditional sorghum beer, depends on enzymes. So do yeast bread in a Kigali bakery, ikivuguto in a village gourd, and the washing powder that removes a grass stain from a school uniform. So does every breath you take.
Enzymes run the chemistry of life, and people have used them for thousands of years, long before anyone knew what they were.
If an enzyme is missing or faulty, illness can follow. Many adults produce little lactase, so the lactose in fresh milk passes undigested into the large intestine, where bacteria ferment it and cause bloating and discomfort. This is lactose intolerance. Fermented milk such as ikivuguto usually causes fewer problems, because bacteria have already used up much of the lactose.
| Use | Enzyme and what it does |
|---|---|
| Malting sorghum for ikigage | Soaked sorghum grain germinates and makes amylase, which turns its starch into sugars; yeast enzymes then ferment the sugars. |
| Bread | Yeast enzymes break down sugar and release carbon dioxide, which makes the dough rise. |
| Ikivuguto and yoghurt | Bacterial enzymes turn lactose into lactic acid, which thickens and sours the milk and helps preserve it. |
| Biological washing powder | Proteases and lipases digest protein stains (blood, egg) and grease at low washing temperatures, saving energy. |
| Meat tenderiser | Papain, a protease from pawpaw (papaya), partly digests the proteins in tough meat. |
| Fruit juice | Pectinase breaks down the pectin in fruit cell walls, so more juice is released and it is clearer. |
| Lactose-free milk | Lactase splits lactose into glucose and galactose. |
| Medicine | Glucose-test strips for diabetes use an enzyme that reacts only with glucose; many medicines work by blocking particular enzymes. |
Question: A biological washing powder packet says "best at 30–40 °C; do not use for boiling wash". Explain this advice.
Solution: The powder contains enzymes (proteases and lipases). Between 30 °C and 40 °C they are near their optimum temperature, so they digest protein and fat stains quickly. In a boiling wash the high temperature would denature the enzymes: their active sites would change shape and they would stop working, so the powder would clean no better than an ordinary one.
Question: A cook wraps tough goat meat in slices of green pawpaw for a few hours before cooking. Explain why the meat becomes tender.
Solution: Pawpaw contains papain, a protease. It breaks down some of the proteins that make the meat tough into shorter chains, so the meat becomes softer. If the meat were boiled first, the papain would be denatured and would not work.
Tip
Exam technique: for any enzyme application, name (1) the enzyme or enzyme group, (2) its substrate and (3) the product or benefit, and (4) mention temperature or pH if the question gives conditions.
Why must large food molecules be digested by enzymes before they can be used?
Solution: Large molecules such as starch and proteins are insoluble and too big to pass through the gut wall into the blood. Enzymes break them into small, soluble molecules (sugars, amino acids, fatty acids and glycerol) that can be absorbed.
Explain why a germinating sorghum grain tastes sweeter than a dry one.
Solution: During germination the grain makes amylase, which breaks down its stored starch into sugars. The sugars taste sweet and supply energy to the growing seedling.
Which enzymes in biological washing powder remove (a) blood stains and (b) oily stains?
Solution: (a) proteases, because blood contains protein; (b) lipases, because oil is a lipid.
A person gets stomach pains after drinking fresh milk but not after eating ikivuguto. Suggest why.
Solution: They may lack enough lactase to digest lactose (lactose intolerance). In ikivuguto, bacteria have already converted much of the lactose into lactic acid, so less lactose is left to cause symptoms.
Summary
Sources and credits
Written by Ganzaa: the uses of enzymes in the body and in industry, the Rwandan examples, the worked examples and the practice questions. The link between enzymes and medicines draws on the OpenStax section above.
