Enzymes

Question 1

What is an enzyme?

Answer 1

An enzyme is a large protein that acts as a biological catalyst by accelerating chemical reactions.

Question 2

What are enzymes made up of?

Answer 2

Like all proteins, enzymes are made up of chains of animo acid, that fold into unique shapes, that enzymes require to perform their function correctly.

Question 3

What is a catalyst?

Answer 3

A catalyst is a substance that increases the speed or rate of reaction, without being changed or used up in the reaction.

Question 4

Draw the lock and key model.

Answer 4

N/a

Question 5

What is involved in Step 1 of the lock and key model?

Answer 5

Substrates and the Enzyme (Active Site). These are complimentary shapes.

Question 6

What is involved in Step 2 of the lock and key model?

Answer 6

Enzyme-Substrate Complex

Question 7

What is involved in Step 3 of the lock and key model?

Answer 7

Product and reusable enzyme

Question 8

Explain step 1 of the lock and key model

Answer 8

The enzyme and the substrate are specific to one another. The enzyme had to be the right shape for the substrate to bind to the active site of the enzyme. When it denatures, changing shape irreversibly, the chemical reaction no longer works.

Question 9

Explain Step 2 of the lock and key model

Answer 9

The substrate has now bound to the active site of the enzyme in the enzyme-substrate complex.

Question 10

Explain step 3 of the lock and key model

Answer 10

The enzyme catalyses the break down of the substrate into products.

Question 11

Flaws of lock and key model

Answer 11

The model is simpler than reality. In reality, the active site changes shape a little for the substrate to bind to it to get a tighter fit. This is called the ‘induced fit’ model of enzyme action.

Question 12

Is the enzyme shape reusable?

Answer 12

Yes

Question 13

What factors affect the rate of enzyme-controlled reactions?

Answer 13

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

Question 14

How does temperature affect enzymes?

Answer 14

Enzymes work best at optimum temperature. Below this, an increase in temperature provides more kinetic or heat energy to the molecules involves and the number of enzyme-substrate collisions increases, as does the rate of reaction. However, beyond this temperature, the enzyme denatures, changing shape irreversibly, and the active site is disrupted. Most human enzymes work best at 37 degrees Celsius, as this is the standard body temperature.

Question 15

Draw graph showing relationship of temperature and enzyme rate of reaction

Answer 15

N/a

Question 16

How does pH affect enzymes?

Answer 16

Enzymes work best at optimum pH. If the pH changes too much from the optimum, the chemical nature of the animo acids can change. This may result in a change in the bonds and so the tertiary structure may break down. The active site will be disrupted, the enzyme denatured.

Question 17

Show the effect of pH on enzyme rate of reaction on a graph

Answer 17

N/a

Question 18

How does enzyme concentration affect enzyme rate of reaction?

Answer 18

At low enzyme concentration, there is more competition for the active sites, and the rate of reaction is low. As enzyme concentration increases, there are more active sites and the reaction can proceed at a faster rate. Eventually, increasing the enzyme concentration beyond a certain point has no effect as the substrate concentration becomes the limiting factor, and it plateaus.

Question 19

Draw a graph to show the effect of enzyme concentration to the rate of reaction

Answer 19

N/a

Question 20

How does substrate concentration affect enzyme rate of reaction?

Answer 20

At low substrate concentration, many active sites are not occupied. This means the reaction rate is low. When more substrate molecules are added, more enzyme-substrate complexes can be formed. As there are more active site, the rate of reaction increases. Eventually, the substrate concentration will have no effect. The active sites will be saturated so no more enzyme-substrate complexes can be formed.

Question 21

Draw a graph to show how substrate concentration affects rate of reaction

Answer 21

N/a

Question 22

How to investigate the effect of enzyme rate of reaction?

Answer 22

• The amylase, starch and buffer experiment
• The trypsin and milk experiment

Question 23

Describe the trypsin and milk experiment.

Answer 23

1. Label two test tubes A and B
2. Using a clean syringe, place 10cm^3 of milk suspension into Tube A
3. Using a clean syringe, place 10cm^3 of Trypsin solution into Tube B
4. Place the tubes in a water bath at 20 degrees Celsius and leave to equibrilate for 5min
5. Pour the contents of Tube B into Tube A and stir. Start the timer
6. Hold the tube against the white card and observe the X through the solution at regular intervals
7. As soon as the X becomes visible through the solution, stop the timer and record your results
8. Repeat the above procedure at temperatures of: 20, 30, 40, 50, 60, 70 and 80 degrees Celsius

Question 24

Explain the amylase, starch and buffer experiment

Answer 24

1. Set up a Bunsen burner, heatproof mat, tripod and gauze.
2. Place a beaker of water on the gauze and adjust the flame to keep the water at about 35°C.
3. Now put two drops of iodine solution into each spot of a spotting tile.
4. Add 2 cm3 of amylase enzyme solution to a test tube.
5. Place 2 cm3 of starch solution into the same tube.
6. Finally add 1 cm3 of pH solution to the tube. This will keep the pH constant.
7. Mix the solution in the test tube and place it into the beaker of water on the Bunsen burner.
8. Use a pipette to remove a few drops of solution every 20 seconds from the test tube and put them into a different well of the spotting tile.
9. Repeat until the iodine solution stops turning black.
10. Record the time this takes.
11. Repeat with different pH solutions.

Question 25

Risk of amylase, starch and buffer experiment

Answer 25

Iodine solution is an irritant. If it touches skin it should be washed off.
Goggles should be worn at all times.

Question 26

Risk of amylase, starch and buffer experiment

Answer 26

Iodine solution is an irritant. If it touches skin it should be washed off.
Goggles should be worn at all times.

Question 27

Graph rules

Answer 27

• Include proper words in the title
• Dot to dot line
• Label in pen, lines in pencil
• Must be over 3/4 of the space given
• Label axises properly

Question 28

Show what to do if you want to skip some numbers on your scale

Answer 28

N/a

Question 29

Table rules

Answer 29

• Write in pen
• Lines in pencil
• Dependent variable on the right and labelled properly
• Independent variable on the left and labelled properly
• Outer edges closed
• Horizontal lines drawn
• Put all results to the same decimal place accuracy

Question 30

Conclusion rules

Answer 30

• Consists of description and explanation
• Include all key words necessary
• Clear structure
• Keep writing clear and concise
• Make sure you have referred to the change in the dependent variable in each flask
• For description, use words such as thermometer, temperature, increase or stays the same
• Refer to dependent and independent variable

Hint:
- Don’t mention kinetic energy. Heat energy is released as a by-product of respiration or waste product

Question 31

What are digestive enzymes?

Answer 31

Carbohydrates, proteins and lipids are large molecules needed by the body for growth, repair and metabolism. However, they are too large to pass through the intestine, so digestive enzymes break them down into smaller molecules.

Question 32

Examples of carbohydrates

Answer 32

• glycogen
• starch
• sucrose — made by glucose and fructose
• glucose

Question 33

What are monosaccharides and disaccharides?

Answer 33

Monosaccharides are the basic building blocks of a carbohydrate, or a simple sugar, such as glucose or fructose. They are joined by enzymes to form disaccharides (two monosaccharides) or polysaccharides (long chains of monosaccharides).

Question 34

What are carbohydrase enzymes?

Answer 34

Carbohydrase enzymes, such as amylase, break down disaccharides into monosaccharides (simple sugars). These are produced in your mouth (saliva), pancreas and small intestine.

Question 35

What are proteins?

Answer 35

Proteins are large molecules made from animo acids joined together to form chains, such as enzymes, haemoglobin, collagen and keratin, giving each protein original or individual properties.

Question 36

What are protease enzymes?

Answer 36

Protease enzymes are responsible for breaking down proteins into amino acids. Then, different enzymes join animo acids together to form new proteins needed by the body for growth and repair. These are produced in the stomach, pancreas and small intestine.

Question 37

What are lipids?

Answer 37

Lipids are fats and oils. Lipids are large molecules made from smaller units of fatty acids and glycerol.

Question 38

What are the digestive enzymes for lipids?

Answer 38

Digestive enzymes such as lipase break down lipids in the diet into fatty acids and glycerol. These are produced in your pancreas and small intestine. Bile also breaks down fats or lipids in the duodenum, produced in the liver, in a process known as emulsification.

Question 39

Is denaturation permanent?

Answer 39

Yes

Question 40

Is denaturation permanent?

Answer 40

Yes

Question 41

What are thermostable enzymes?

Answer 41

Some enzymes (e.g. in biological washing powders) are thermostable, meaning they can work at a wide range of temperatures.
This allows biological washing powder to be used at low temperatures that saves energy and money.

Question 42

What happens to enzyme bonds due to temperature (hint: denaturing)?

Answer 42

As you increase temperature further, bonds in the active site begin to break, and the tertiary structure is disrupted. This alters the specific shape of the active site, so it may no longer be complementary to the substrate. Heat can break hydrogen and ionic bonds, which disrupts the shape of the enzyme and will change the shape of the active site. Cold temperatures do not denature enzymes because cold does not cause chemical bonds to break.

Question 43

Why does the body need energy in exercise?

Answer 43

Muscles need energy to contract. As muscles contract, the demand for oxygen, hydrogen and other key nutrients increases. The human body requires a continuous supply of energy to perform its many functions. As energy demands increase with exercise, additional energy must be supplied or the exercise will end. Muscle contraction or any form of exercise requires a constant supply of energy in the form of ATP.