Proteins (Edexcel International A Level (IAL) Biology): Exam Questions

People with lactose intolerance cannot digest lactose.

Lactose intolerance is due to a lack of the enzyme lactase.  

(i) Which are the products of lactose digestion?

(1)

☐ A fructose and galactose
☐ B fructose and glucose
☐ C galactose and glucose
☐ D glucose and glucose

(ii) Explain how the three-dimensional structure of lactase affects the mechanism of action of this enzyme.

(3)

People with lactose intolerance can drink lactose-free milk.

Lactose-free milk is produced by treating milk with lactase.

There are two ways of removing lactose from milk:

• Mixing a solution of lactase with the milk (free lactase)

  • Enclosing the lactase inside permeable beads and pouring the milk over them (immobilised lactase).

The diagrams show these two methods.

(i) Suggest one advantage of using immobilised lactase.

(1)

(ii) The table shows the effect of pH on the activity of free lactase and immobilised lactase.

Explain the effects of pH on the activity of these two enzymes.

(4)

(iii) Suggest how the rate of activity of the lactase could be measured.

Include appropriate units in your answer.

(2)

Congenital lactose intolerance (CLI) is an extremely rare genetic disorder.

Most people with CLI are found in one country.

Suggest why most people with CLI are found in one country.

The primary structure of a protein determines its secondary structure and its three‐dimensional structure.

Read through the following account of the primary structure of a protein.

Complete the account by writing the most appropriate word or words on the dotted lines.

The primary structure of a protein is the specific sequence of amino acids joined together by .................................................... bonds.

These bonds are formed between the ................................................ group of one amino acid and the ..................................................... group of an adjacent amino acid by a .......................................................  reaction.

These bonds are formed during the stage of protein synthesis called ...............................................  .

The table describes the types of bond that hold the secondary and the three‐dimensional structures together.

Which type of bonding is true for each structure?

Catalase is an enzyme that breaks down hydrogen peroxide into water and oxygen. A student investigated the effect of the concentration of catalase on the initial rate of this reaction.

Identify the independent variable and the dependent variable in this investigation.

State two variables that should be controlled to ensure that the results are valid. For each variable, describe how it could be controlled.

The table below shows the volume of oxygen produced over 60 seconds using a 5% catalase solution.

Plot a graph of these results and draw a line of best fit

Use your graph to determine the initial rate of reaction.

Suggest an explanation for the rate of reaction between 40 and 60 seconds.

The graph shows the volume of product formed during an enzyme controlled reaction over 60 seconds.

Calculate the average rate of reaction for the first 10 seconds.

The study in (a) also tested a competitive inhibitor of the enzyme.

Explain why a competitive inhibitor reduces the rate of reaction at low substrate concentrations.

Scientists recorded the dietary vitamin C intake of 500 adults using self-reported food diaries over a six-month period, and observed a positive correlation between high vitamin C intake and reduced incidence of atherosclerosis.

A student concluded from this that improving vitamin C intake would reduce heart disease.

Assess this conclusion.