Grade 10 Biology TEST on Enzymes

Question 1

1. Catalase is the enzyme that catalyzes the breakdown of hydrogen peroxide (H2O2) to water and oxygen. Can you write the balanced chemical equation for this reaction?

Answer 1

2H2O2 → 2H2O + O2

Question 2

Enzyme characteristics

Answer 2

• Are biological catalysts (speeds up chemical reactions/increases the reaction rate).
  > Are not consumed in the chemical reaction (reusable)
• Enzymes are specific
  > Each type of enzyme can catalyse only ONE type of chemical reaction.
  > For example, photosynthesis can not speed up with a catalase.
• Enzymes are proteins (4 molecules - proteins, carbohydrates, lipids, nucleic acids)
• Enzyme performance is affected by changes in temperature and pH.

Question 3

Active site structure

Answer 3

• The substrates bind to the active site, the active site then catalyses the reaction.
• What is binding? –> a formation of a weak chemical bond
• When the substrates bind to the active site some chemical bonds are broken while some are formed.

Question 4

What determines how the substrate binds to the enzyme active site?

Answer 4

The physical (shape) and chemical (+,-) properties of the active site and the substrate.
- these allow the substrate and active site to be complementary to each other (they “match”).
- they fit together like a lock and key.

Question 5

How do the substances and enzyme actually meet often enough to react?

Answer 5

Random particle motion
- Because they move so quickly - hypermotion.

Question 6

Collision Theory

Answer 6

1. Particles must collide with one another in order to react.
2. The collision must have sufficient energy (collision speed).
3. Collision must be in the correct orientation.

Question 7

Enzymes

Answer 7

are biological catalysts that speed up the rate of chemical reactions. Enzymes are all proteins and each enzyme acts on one type of substrate.

Question 8

Temperature

Answer 8

a measure of average particle speed of a substance.
- by increasing the temperature of a substance, we raise particle speed.

Question 9

Rate

Answer 9

a change in something over time

Question 10

How do enzymes function?

Answer 10

Binding of substrates to active site, “lock-and-key,” enzyme-substrate complex, active site catalyzes the reaction, products are released.

The ‘lock and key’ model of enzyme action is when the substrate fits into the active site of the enzyme allowing for a reaction and also proving they are complementary.
Each enzyme will act only on one substrate because the enzyme must combine in order to form an enzyme-substrate complex, like a ‘lock and key’
(page 2)

Question 11

Proteins

Answer 11

are long chains of subunits called amino acids. Neighboring amino acids in the chain are joined by strong covalent bonds.

Question 12

Measure the rate of a reaction

Answer 12

Measure how the quantity of A and B decrease over time.
Measure how the quantity of C and D increase over time.

Question 13

Why does the rate of a chemical reaction decrease at low temperature?

Answer 13

• At low particle speeds, the frequency of collisions decrease.
• At low particle speeds, the collisions that do occur, have a lower probability of resulting in a successful reaction.

Question 14

Structure of an enzyme as a proteins

Answer 14

A protein is a large polymer made of many amino acid subunits connected in a long chain (picture page 8)

Question 15

How is the three dimensional structure of the enzyme specified and maintained?

Answer 15

The structure of an enzyme determines its function
- chemical bonds of varying strengths connect non-neighbouring amino acids.
> covalent and ionic bonds are relatively strong
> hydrogen bonds are relatively weak.

Question 16

Enzyme denaturation.

Answer 16

If the structure of the enzyme is altered, the enzyme becomes denatured. Denaturation of the active site prevents the substrates from binding; the enzyme will not be able to catalyze the reaction; the reaction rate will decrease.

Question 17

What is occuring in the enzyme when it becomes denatured by high temperatures?

Answer 17

• The high temperature causes particle speeds to increase with 2 EFFECTS:
  1. particles in the solution collide with the enzyme at higher energy - these collisions may break and weaker bonds holding non-neighbouring amino acids together.
  2. Greater ‘shaking’ of the enzyme may result in breaking weaker bonds (hydrogen bonds) between non-neighbouring amino acids.

Question 18

How does changing the temperature affect the rate of an enzyme-catalyzed reaction?

Answer 18

Raising temperature generally speeds up a reaction, and lowering temperature slows down a reaction. However, extreme high temperatures can cause an enzyme to lose its shape (denature) and stop working.

Question 19

At low temperatures:

Answer 19

the reactants/enzymes do not collide with sufficient energy to lead to a successful reaction.

Question 20

At high temperatures

Answer 20

the increased particle motions denature enzymes by breaking the weaker chemical bonds that maintain the enzyme’s 3-D structure, especially in the active site.

Question 21

Optimum temperature

Answer 21

• Particle speeds are high enough to cause sufficient successful reactions.
• But they are not so high as to cause denaturation.

Question 22

In a beaker of water

Answer 22

Some of the water molecules (H2O) may ionize – the molecule splits into an H+ ion and an OH- ion. Or comes back together - a reversible reaction. (page 10)

Question 23

What is pH?

Answer 23

pH describes the relative concentrations of H+ and OH- in an aqueous solution.
- Acid = excess H+
- Alkali = excess OH-.
A neutral solution has equal concentrations of H+ and OH-
(page 10)

Question 24

How does changing the pH affect the rate of an enzyme-catalyzed reaction?

Answer 24

• Each enzyme has an optimum pH, where the rate of enzymatic reaction is maximum.
• At low and high pH, the enzymes denatures
  1. the protein’s shape changes
  2. chemical bonds are broken
  3. active site of the enzyme can not bind to substrates.
  4. this decreases the enzyme’s catalytic ability.
  5. the reaction rate goes down.
• Denaturation occurs: weak chemical bonds between non-neighbouring amino acids maintain the enzyme structure.

Question 25

Where enzymes function

Answer 25

Most enzymes function in the cell cytoplasm, where they control the cell’s metabolism. Some enzymes function in an extracellular environment – e.g. digestive enzymes secreted by digestive tract organs.

Question 26

What does it mean if an enzyme is “specific”

Answer 26

specificity refers to the enzyme’s ability to avoid unwanted reactions in its active site
- reaction specificity (in which the enzyme catalyzes a specific reaction but not other reactions with the same substrate)
Substrate specificity (an enzyme catalyzes a specific reaction with one substrate but does not catalyze the same reaction with another substrate)

look at paper

Question 27

How does specificity depend on the structure of the active site?

Answer 27

the three-dimensional structure of the active site of an enzyme allows the enzyme to bind easily to specific substrates only.

Question 28

Describe and explain the shapes of the graphs:
a. the effect of temperature on the rate of an enzyme-catalyzed reaction;

Answer 28

bell-shaped curve, with the reaction rate initially increasing with temperature, reaching an optimal point, and then decreasing due to enzyme denaturation from further temperature increase.

Question 29

Describe and explain the shapes of the graphs:
b. the effect of pH on the rate of an enzyme-catalyzed reaction?

Answer 29

bell-shaped curve, each enzyme has an optimum pH range. Changing the pH outside of this range will slow enzyme activity. Extreme pH values can cause enzymes to denature.

Question 30

Chemical bond

Answer 30

A charge attraction between + and -

In an ACID:
- excess H+ can steal the negatively charged amino acid
- the amino acids are no longer attracted to one another - the bond breaks, and the structure changes.
- if enough bonds are broken , the enzyme becomes denatured.
(page 14)

Question 31

Particles in a beaker with rising temperature

Answer 31

• water particle collides with the glass particles.
• the glass particle will vibrate faster.
• the alcohol particles will move at a higher speed inside, increasing the volume.

Question 32

Catalase

Answer 32

is the enzyme that catalyzes the breakdown of hydrogen peroxide (H2O2) to water and oxygen