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Enzymes are biological catalysts, usually proteins. A substrate binds at an active site with a complementary shape, allowing a reaction to happen more rapidly. Raising temperature initially increases rate but excessive heat can change enzyme shape and denature it. A change in pH can also affect the active site. Low temperature usually slows an enzyme without permanently destroying it. State what happens to binding rather than saying the enzyme simply dies.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Explain enzyme specificity and denaturation
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: What is denaturation?
A change in protein shape affecting function. The active site may no longer bind substrate effectively.
After watching 2: Which enzyme group digests proteins?
Proteases. They produce amino acids from protein chains.
What you'll be able to do
Enzymes are biological catalysts, usually proteins. A substrate binds at an active site with a complementary shape, allowing a reaction to happen more rapidly. Raising temperature initially increases rate but excessive heat can change enzyme shape and denature it. A change in pH can also affect the active site. Low temperature usually slows an enzyme without permanently destroying it. State what happens to binding rather than saying the enzyme simply dies.
Amylase breaks starch into smaller sugars, proteases break proteins into amino acids and lipases break lipids into fatty acids and glycerol. Bile neutralises stomach acid and emulsifies fats, increasing surface area for lipase; it is not an enzyme. The small intestine has villi, a large surface and a thin barrier for absorption. Some products enter blood, while absorbed lipids use a different route through lymph vessels.
Benedict’s solution with heating tests for reducing sugars, iodine for starch, Biuret reagent for protein and an appropriate lipid test for fats. Use controls and the correct observed colour change. To investigate amylase with starch, vary one factor, hold other conditions constant and use iodine samples at regular times. Inverse time is useful when the same fixed endpoint is used. Repeats improve confidence but do not repair an unfair comparison.
Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.
Common mistakes to avoid
Key takeaways
Question 1: Starch disappears in 40 s at one pH and 20 s at another. Compare relative rates.
The second relative rate is twice as large.
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.