Enzymes as catalysts at Higher Level: The same statement as SL. HL questions ask what is true of every enzyme, then build on it with inhibition and control of pathways later in this topic.
Practise this as you read
- Identify a feature shared by all enzymes.
- Explain why cells need catalysts.
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The big idea: An enzyme is a biological catalyst: it speeds up a reaction and is not used up, so the same enzyme molecule works again and again.
The points to remember
- Every enzyme acts on a substrate: the substrate binds and is changed into products.
- The enzyme is unchanged at the end, so a small amount of enzyme can convert a lot of substrate.
- Without enzymes, most reactions in cells would be far too slow at body temperature to keep the cell alive.
- Heating a cell to speed reactions up would damage its proteins, so cells use enzymes instead.
Remember it as: Faster, and not used up.
Real example: carbonic anhydrase. In red blood cells, carbonic anhydrase joins carbon dioxide and water into carbonic acid. One enzyme molecule can do this up to a million times a second, so carbon dioxide is picked up from respiring tissues as fast as it is made.
Trap: An enzyme does not make a reaction happen that could not happen at all. It makes a possible reaction go much faster.
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How it is asked: Expect a multiple-choice question on what is true of all enzymes, or a short explanation of why cells need catalysts.
IB-style questionExplain[3 marks]
Explain the benefit to living organisms of enzymes acting as catalysts.
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See the answer broken into clear points, with guidance on how each point earns marks.