Proteins (SQA National 5 Biology): Exam Questions

A 100 g sample of haemoglobin was found to contain 15 g of leucine.

What mass of leucine would be found in a 5 g sample of haemoglobin?

The enzyme invertase is commonly used to make soft-centred chocolates.

Invertase speeds up the following reaction:

sucroseglucose + fructose

An investigation into the effect of pH on invertase at different temperatures was carried out.

The results are shown in the graph.

(i) Identify the temperature at which invertase was most active.

[1]

...............................°C

(ii) State the optimum pH of invertase.

[1]

pH..........................

(iii) Predict what would happen to the enzyme activity if the investigation was repeated at 75 °C.

[1]

(iv) Describe how this investigation could be changed to find a more exact optimum temperature of invertase.

[1]

A different enzyme speeds up the following reaction:

starch maltose

Explain why invertase would not speed up this reaction.

Which diagram shows the concentration of product during a degradation reaction?

A group of scientists investigated the effect of temperature on the growth of genetically modified (GM) cells. The GM cells were grown in a nutrient solution at 20 °C. This was repeated at 30 °C and 40 °C using fresh nutrient solutions at each temperature.

Which of the following would improve the reliability of the results?

Potatoes store sugar in the form of starch. Glucose‑1‑phosphate (G‑1‑P) molecules are converted to starch in an enzyme‑controlled reaction.

This enzyme can be found in potato extract.

(i) Identify the type of reaction carried out by this enzyme.

[1]

(ii) Identify the substrate in this reaction.

[1]

An experiment was set up to investigate the time taken for starch to be produced. All previously made starch was removed from the potato extract.

Two rows of a dimple tile were set up as shown in the diagram.

At 5‑minute intervals the content of the dimples in each column was tested for the presence of starch.

The results are shown in the table.

(i) Suggest a reason for any previously made starch being removed from the potato extract.

[1]

(ii) State two variables that should be controlled to make this experiment valid.

[2]

1. ...........................................................................................

2. ...........................................................................................

(iii) Explain how the results show that the enzyme is required for the reaction to occur.

[1]

Which of the following statements is true for proteins?

1. They are made in the nucleus.

2. They are affected by temperature.

3. They can be found in the cell membrane.

4. They all function as enzymes.

Pepsin is an enzyme involved in the digestion of proteins, which is a degradation reaction.

The diagram represents three stages that occur in this reaction.

(i) Using letters from the diagram, put the stages into the correct order to show this degradation reaction.

[1]

stage............. stage ............. stage .............

(ii) Describe the feature of pepsin that allows it to bind to only one substrate.

[1]

The graph shows the results of an experiment to investigate the effect of pH on pepsin activity.

Use the graph to identify the optimum pH of pepsin.

pH................................

Enzymes can be denatured by changes in pH.

Give a reason why the rate of reaction will be affected.

The diagram represents three stages in an enzyme-controlled reaction.

Which row in the table identifies the labelled structures?

An investigation was carried out into the breakdown of cooked egg white by enzymes.

2 g of cooked egg white was placed in each of four test tubes containing different enzyme solutions at different pH levels as shown.

The test tubes were placed in a water bath at 37 °C for 2 hours.

The cooked egg white was then removed and weighed.

The results are shown in the table.

Complete the table by calculating the change in mass of the egg white in test tube A.

(i) Explain why the change in mass in test tube B was less than in test tube A.

[1]

(ii) Explain why there was no change in mass in test tubes C and D.

[1]

If the investigation was repeated at 70 °C, describe the change in the:

(i) structure of the active site of the enzymes

[1]

(ii) rate of the reaction in test tubes A and B.

[1]