Chapter 5: Enzymes

Question 1

Define a catalyst [2]

Answer 1

a substance that increases the rate of a chemical reaction and is not changed by the reaction

Question 2

Define an enzyme [2]

Answer 2

proteins that function as a reusable bio-catalyst which increase the rate of reaction without getting involved in the reaction

Question 3

What do enzymes do? [3]

Answer 3

1. Speed up reactions (without them reactions may happen too slowly or not at all)
2. Reduce activation energy (reactions take place at lower temperatures)
3. Act as catalysts and can be reused

Question 4

State 5 different enzymes along with their related substrate and the product formed [5+5+5]

Answer 4

Enzyme Substrate Product
Protease Proteins Amino Acids
Lipases Lipids Glycerol & Fatty acids
Amylase Starch Simple sugars/maltose
Maltase Maltose Glucose + Glucose
Sucrase Sucrose Glucose + Fructose

Question 5

How do enzymes work? Describe the step by step process. [4]

Answer 5

Each enzyme has molecules that have an active site which has a specific shape and structure which is complimentary to that of the substrate it needs to catalyze. The substrate therefore fits perfectly with the active site of the enzyme, allowing them to bind together to form an enzyme-substrate complex. After this, the substrate is broken down and becomes the product. Since the products have a different shape than that of the active sites, they are released. The enzyme remains unchanged and can be reused.

Question 6

What is necessary for all chemical reactions to take place? [1]

Answer 6

Water

Question 7

Define an active site [1]

Answer 7

The site on an enzyme where the substrate binds. It has complimentary shape and size to the substrate.

Question 8

What are the factors affecting enzymatic activity [4]

Answer 8

1. Temperature
2. pH
3. Substrate concentration
4. Enzyme concentration

Question 9

When are enzymes denatured? [2]

Answer 9

Enzymes are denatured at extreme temperatures and pH.

Question 10

What does an enzyme getting denatured mean? [1]

Answer 10

Their active sites get deformed/altered irreversibly so they can no longer bind to the substrate.

Question 11

Define optimum temperature/pH [1]

Answer 11

The temperature/pH at which rate of reaction is at its maximum.

Question 12

As temperature increases, what happens to enzyme activity? [4]

Answer 12

Temperatures below optimum: low temperature, so less kinetic energy, meaning less successful collisions, meaning low activity, so less substrate is turned into product
Temperature increasing towards optimum: increasing temperature, more successful collisions, more enzymes and substrates have enough kinetic energy, so more activity, so more substrate turned to product
Optimum temperature: most substrate turned to product due to highest enzyme activity
Higher than optimum temperature: active site gets deformed, so decrease in collisions, eventually get denatured meaning no activity

Question 13

Design an experiment to prove temperature affects enzymatic reactions [6]

Answer 13

Independent variable: temperature
Dependent variable: time for bubbling to stop
Controlled variable: volume of H2O2 (hydrogen peroxide) and volume of catalase enzyme
Method: Take 6 identical test tubes and fill each one with 5ml of H2O2 solution. Start a water bath. Label each test tube as A, B, C, D, E, F. Heat test tube “A” to 15°C. Heat test tube B, C, D, E, F to 25°C, 35°C, 45°C, 55°C, 65°C respectively. Keep a thermometer in the test tube to monitor the temperature. Keep a stopwatch ready, set to 0 seconds. Add the catalase enzyme to test tube A and start the stopwatch. Stop when the bubbles of oxygen stop forming. Record the data and repeat this process for all the other test tubes labeled. Repeat the experiment multiple times to gain accurate results.
Safety precautions: wear a lab coat, goggles and gloves. Stand up while conducting experiment and beware of fire.