Question 1: Define the Lock and Key Theory as it relates to enzyme activity.

Answer: The Lock and Key Theory describes how enzymes and substrates fit together precisely, like a key fitting into a specific lock, enabling the enzyme to catalyse a specific chemical reaction.

Question 2: Explain why enzymes are specific to particular substrates according to the Lock and Key Theory.

Answer: Enzymes are specific because their active sites have a unique shape that only fits specific substrate molecules, similar to a key fitting into a particular lock.

Question 1: If an enzyme catalyses the breakdown of 120 μmol of substrate in 10 minutes, what is the rate of reaction in μmol per minute?

Answer: 12 μmol per minute

Question 2: Calculate the enzyme's activity if 50 mg of enzyme breaks down 200 μmol of substrate in 5 minutes. Show your formula and units.

Answer: Enzyme activity = (amount of substrate broken down) / (mass of enzyme × time) = 200 μmol / (50 mg × 5 min) = 0.8 μmol/mg/min

Question 1: Describe an experiment to test how temperature affects enzyme activity, including variables and safety precautions.

Answer: An experiment can involve measuring enzyme activity at different temperatures (e.g., 20°C, 30°C, 40°C). Independent variable: temperature; dependent variable: rate of reaction; control variables: pH, substrate concentration. Safety precautions include wearing safety goggles, handling hot equipment carefully, and disposing of chemicals properly.

Question 2: Identify two variables that should be kept constant in an experiment testing enzyme activity, and explain why.

Answer: Variables such as pH and substrate concentration should be kept constant to ensure that any changes in enzyme activity are due to the independent variable being tested, such as temperature.

Question 1: In an experiment, enzyme activity increased with temperature up to 37°C and then decreased. Explain this pattern using the Lock and Key Theory.

Answer: The increase up to 37°C indicates that higher temperatures enhance molecular movement, increasing enzyme-substrate collisions. Beyond 37°C, enzymes denature, losing their active site shape, which reduces activity, aligning with the Lock and Key Theory where the active site can no longer fit the substrate.

Question 1: Describe how the Lock and Key Theory explains the specificity of enzymes for their substrates. (6 marks)

Answer: The Lock and Key Theory states that enzymes have specific active sites shaped to fit particular substrates. This shape complementarity ensures that only specific substrates can bind, making the enzyme highly selective. The enzyme's active site acts like a lock, and the substrate acts like a key, fitting precisely to enable the chemical reaction to occur efficiently.

Question 1: Explain how the Lock and Key Theory is utilised in the design of enzyme-based medicines.

Answer: Medicines often mimic the shape of natural substrates to fit into specific enzyme active sites, blocking or enhancing their activity. This relies on the Lock and Key Principle to ensure high specificity and effectiveness of the drug.

Question 2: Discuss one limitation of the Lock and Key Theory and how the induced fit model addresses it.

Answer: A limitation of the Lock and Key Theory is that it suggests a rigid active site, but in reality, enzymes are flexible. The induced fit model explains this by proposing that the active site molds around the substrate during binding, allowing for a better fit and more accurate explanation of enzyme activity.