Factors and conditions affecting the activity of enzymes

Which statements describe some enzyme actions?

1 Enzymes hold reacting molecules so that their reactive groups are close together.

2 In an enzyme-catalysed reaction, more molecules have sufficient energy to react

than in the absence of the enzyme.

3 Reactions catalysed by enzymes take place at a lower temperature than they would

without the enzyme.

• 1, 2 and 3   

• 1 and 2 only   

• 1 and 3 only 

• 2 and 3 only

In a reaction controlled by an enzyme, which of the following graphs shows the effect of substrate concentration on the rate of the reaction?

• A

• B

• C

• D

What determines the specificity of an enzyme?

 1 the covalent and other bonding between R groups of the polypeptide

 2 the optimum pH of the enzyme

 3 the covalent peptide bonds between amino acids of the polypeptide

 4 the shape of the substrate molecule

• 1, 2, 3 and 4

• 1 and 3 only

• 1 only   

• 2, 3 and 4 only

Apart from oxygen, what product is made when hydrogen peroxide breaks down?

• H₂O

• СO₂

• H₂O₂

• SO₂

The graph shows the progress of the digestion of starch by the enzyme salivary amylase. Why does the reaction slow down?

• End-product inhibition by maltose

• The salivary amylase is becoming denatured

• The salivary amylase is gradually becoming saturated with starch

• There are fewer and fewer substrate molecules left to bind with the salivary amylase

The graph shows the effect of temperature on the rate at which the enzyme in a biological washing powder digests and removes fruit juice stains.

Which statements explain the shape of the graph at temperatures higher than X?

 1 Bonds are broken between the R groups of the amino acids in the polypeptide chains of

the enzyme.

 2 There are more collisions between the enzyme and its substrate.

 3 The tertiary structure of the enzyme is altered.

 4 The shapes of the active site and the substrate are no longer complementary.

• 1, 2 and 3  

• 1, 2 and 4

• 1, 3 and 4

• 2, 3 and 4

State the volume of distilled water that is added to 5 cm³ of 6 % hydrogen peroxide to prepare 5% hydrogen peroxide solution.

• 0.08 cm³

• 0.8 cm³

• 8 cm³

• 80 cm³

Name the independent and dependent variables in this experiment

• Independent variable: conc. of . actual rate of reaction

  Dependent variable: rate of H₂O_2.

• Independent variable: conc. of rate of reaction.

  Dependent variable: rate of H₂

• Independent variable: conc. of time.

  Dependent variable: rate of H₂O

• Independent variable: conc. of H₂O_2.

  Dependent variable: rate of O₂

Describe the shape of the graph

• In these conditions, reaction rate is directly proportional to the enzyme concentration

• The initial rate of the reaction increases linearly until the end of the reaction

• At low concentrations, the graph will show an increasing rate of reaction as concentration increases, leveling off at higher concentrations

• At low concentrations the graph will show an increase in reaction rate and at high enzyme concentrations it will show a plateau.

Identify ONE possible source of error during this experiment

• Incorrect formulation of the hypothesis

• Incorrect design of the experiment

• Incorrectly identify the dependent and independent variables

• Incorrect measurements of hydrogen peroxide and mashed potatoes; incorrect concentration of hydrogen peroxide