This memory aid covers Memory Aids within Enzymes in Digestion for GCSE Biology. Enzyme structure and function, digestive enzymes, factors affecting enzyme activity, lock and key model, and practical investigations It is section 16 of 19 in this topic. Use it for quick recall, then test yourself straight afterwards so the memory aid becomes usable in an answer.
Topic position
Section 16 of 19
Practice
20 questions
Recall
25 flashcards
Memory Aids
Lock and Key: Picture a padlock (enzyme) with a keyhole (active site). Only one specific key shape (substrate) will fit. If you bend the lock with heat, no key will ever work again — that is denaturation.
Remembering which enzyme digests what — PLP, LLL, ALA:
- Protease Loves Proteins
- Lipase Loves Lipids
- Amylase Loves Amylose (starch)
Enzyme locations — "Stomach Pepsin, Pancreas Produces All Three, Intestine Trypsin Lives":
- Mouth + Pancreas: Amylase
- Stomach only: Pepsin
- Pancreas + Small intestine: Trypsin, Lipase
Bile is not an enzyme: Bile Breaks fat Into Little Emulsions — but it does not break chemical bonds. It is produced by the liver, stored in the gall bladder, and works in the small intestine (duodenum).
Quick Check: A student heats an amylase solution to 80°C for five minutes, then cools it back to 37°C and adds starch. Explain why starch is not broken down.
Heating to 80°C has denatured the amylase. The high temperature broke the bonds maintaining the enzyme's three-dimensional shape, permanently altering the active site. When cooled, the active site does not return to its original complementary shape. The starch (substrate) can no longer fit into the active site, so no enzyme-substrate complexes form and digestion cannot occur. Cooling reverses the slowing of reaction rate caused by low temperature, but it does not reverse denaturation, which is permanent.
Quick Check: A student adds extra lipase to a fat emulsion and finds the rate of reaction increases at first but then reaches a plateau. Using your knowledge of enzyme kinetics, explain why the rate stops increasing.
At low enzyme concentrations, adding more lipase increases the number of active sites available, so more substrate molecules can be converted at any one time — the rate increases. However, once the enzyme concentration is high enough that all substrate molecules are continuously occupied with enzyme active sites, adding more enzyme makes no difference. The substrate concentration has become the limiting factor. All substrate molecules are already bound to an enzyme, so the reaction is at its maximum rate (Vmax). To increase the rate further, more substrate would need to be added.
Quick Check: Pepsin works in the stomach (pH 1.5). When food moves into the small intestine, bile raises the pH to around 8.5. Explain why this is important for the digestion of proteins in the small intestine.
Pepsin would be denatured or highly inactive at pH 8.5 — it is adapted to acidic conditions. The small intestine uses a different protease enzyme, trypsin, which has an active site shaped for its substrate at the optimum pH of 8.5. Bile neutralising the stomach acid raises the pH to the optimum for trypsin, allowing it to work efficiently. This also prevents trypsin from being denatured by low pH. The switch from pepsin to trypsin at different pH values means protein digestion can continue in two different organs using enzymes adapted to each location.