Practise CAIE AS Biology 3.1 by explaining enzyme specificity and catalytic action, then interpreting investigations that track substrate or product change.
The diagram shows a simple metabolic pathway.
The letters W, X, Y and Z represent four different substances. At each step in the diagram the substrate undergoes a chemical reaction catalysed by an enzyme. The reaction produces the next substance in the pathway.
Which statements correctly describe the enzymes taking part in this metabolic pathway?
1 They are all globular proteins.
2 They all have the same tertiary structure.
3 They all contain hydrogen atoms in their structure.
1, 2 and 3
1 and 2 only
1 and 3 only
2 only
The diagram shows different molecules in a solution.
Which statement could explain what happens when some of the molecules are mixed together?
Molecule P forms an enzyme-substrate complex with the non-competitive inhibitor molecule Q .
Molecule Q binds to molecule P, increasing the activation energy.
Molecules R and S bind to the active site of molecule P .
Molecules S and R are the products of the breakdown of molecule P .
Influenza virus has an enzyme called neuraminidase which breaks down glycoproteins in the surface membrane of the cell that the virus will infect. The glycoprotein binds to the active site of neuraminidase by induced fit.
Which statements about the induced fit hypothesis of enzyme action are correct?
1 The active site must have the same shape as the substrate for them to bind together.
2 This enzyme is less likely to be affected by non-competitive inhibitors than an enzyme working by the lock-and-key mechanism.
3 The substrate is converted to product by specific R-groups in the active site just like the lock-and-key mechanism.
1 and 2
2 and 3
2 only
3 only
A student investigated the effect of enzyme concentration on the rate of hydrolysis of protein in milk.
When the enzyme and milk were mixed, the protein was hydrolysed and the mixture changed from cloudy to clear.
The student investigated five different enzyme concentrations and recorded the time taken for the mixture to become clear.
What is an appropriate control for this investigation?
Carrying out an experiment where the enzyme solution is replaced with water.
Carrying out each experiment in a thermostatically controlled water-bath at .
Repeating each experiment three times for each of the five enzyme concentrations.
Using the same volume of enzyme solution for each of the five experiments.
A scientist investigated the progress of two enzyme-catalysed reactions in separate test-tubes, X and Y . Both reactions result in colour changes that can be detected using colorimetry.
samples were taken from each test-tube at the start of the investigation and at regular intervals for the next 5 minutes. Copper ions were added to each sample as soon as the sample was collected to inactivate the enzymes and stop the reactions from progressing further.
The absorbance of each sample was measured using a colorimeter.
The graph shows the results of this investigation.
Which statement is consistent with the results shown in the graph?
The substrate in test-tube X has a higher absorbance than the product.
The product in test-tube Y has a lower absorbance than the substrate.
The rate of the reaction in test-tube X increased with time.
The rate of the reaction in test-tube Y increased with time.