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Enzymes and investigations

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Which distinguishes induced fit from a rigid lock-and-key model?

  1. Binding can change the enzyme's conformation.
  2. Only induced fit involves a substrate-binding active site.
  3. The active site remains rigid throughout substrate binding.
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Binding can change the enzyme's conformation.

The active site can adjust during productive binding.

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Which is NOT true of an enzyme?

  1. It supplies energy to the substrate
  2. It binds only substrates of a complementary shape
  3. It is unchanged at the end
  4. It lowers the activation energy
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It supplies energy to the substrate

An enzyme lowers activation energy; it does not supply energy.

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A high-temperature rate falls. Which explanation is appropriate?

  1. The enzyme is denatured, so the 3D shape of the active site is no longer complementary to the substrate.
  2. Particles now move more slowly, so fewer collide with the active site.
  3. Heat hydrolyses the peptide bonds, so the enzyme falls apart into amino acids and the active site is lost.
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The enzyme is denatured, so the 3D shape of the active site is no longer complementary to the substrate.

Fewer enzyme-substrate complexes form, which outweighs the higher frequency of collisions.

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What would usually raise the high-substrate plateau while keeping conditions suitable?

  1. Diluting the enzyme while keeping substrate saturating.
  2. Adding substrate indefinitely to the same saturated enzyme amount.
  3. Adding more active enzyme.
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Adding more active enzyme.

More active sites increase total catalytic capacity.

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At a high substrate concentration, the rate of an enzyme reaction stays constant. Which statements explain this? 1: All active sites are occupied. 2: The enzyme has been denatured. 3: Enzyme concentration is now limiting. 4: Substrate molecules have stopped moving.

  1. 3 and 4 only
  2. 1, 3 and 4 only
  3. 1 and 3 only
  4. 1, 2 and 3 only
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1 and 3 only

At saturation every active site is busy, so the amount of enzyme limits the rate. The enzyme is not denatured and molecules keep moving.

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Which improvement directly addresses coarse amylase endpoint timing?

  1. Repeat the same coarse sampling schedule without shortening intervals.
  2. Use shorter, consistent sampling intervals near the endpoint.
  3. Use longer sampling intervals so the colour difference is easier to see.
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Use shorter, consistent sampling intervals near the endpoint.

This narrows the uncertainty in when the endpoint occurred.

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Question 1 of 7

Explain catalysis

4 marks

Explain enzyme specificity and catalysis using active site, enzyme-substrate complex, induced fit and activation energy. [4]

Connect the terms causally rather than listing them.

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