Factors that Affect Enzyme Action (CIE AS Biology)

Fig. 1 shows the results of an investigation into the effects of pH on the activity of two enzymes (X and Y) taken from two different parts of the human digestive system.

Fig. 1

Contrast the activity of enzymes X and Y in Fig. 1.

State the role of a buffer solution when investigating the effect of pH on the rate of the reaction.

Table 1 shows the results of an investigation into the effects of temperature on the reaction rate of amylase. Note that a.u. denotes arbitrary units.

Table 1

Explain the results when the temperature increased above 40 °C.

Calculate the percentage increase in the reaction rate between 10 °C and 40 °C. 

Explain the effect that increasing the concentration of an enzyme would have on the rate of a reaction.

Sketch a graph showing enzyme concentration against the rate of reaction when the amount of substrate is limited.

Hydrogen peroxide is broken down by the enzyme catalase into water and oxygen. Catalase can be found inside most types of living cells, including potato cells.

A group of students investigated the effect of various concentrations of hydrogen peroxide on the reaction rate of catalase. They ground up a 3 cm piece of potato cylinder with 5 cm³ of distilled water to provide a solution containing catalase. They then made a serial dilution of the original 100 % stock solution of hydrogen peroxide before setting up three test tubes for each concentration of hydrogen peroxide. For each test tube, they dipped a filter paper disc into the catalase suspension and placed the disc at the bottom of the test tube containing 10 cm³ of hydrogen peroxide. They measured the time taken for the disc to float up to the surface of the hydrogen peroxide solution.

Their results are shown in Table 1.

Table 1

Calculate the reaction rate for the 100% hydrogen peroxide concentration. Show your working.

Explain the results of the investigation shown in Table 1.

Trypsin is an enzyme produced by the pancreas that hydrolyses proteins in the small intestine. 

The activity of trypsin was investigated by placing a small amount of the enzyme with a known concentration of protein.

Fig. 1 shows the progress of this reaction when it is carried out at 25 °C.

Fig. 1

Calculate the initial rate of the reaction in Fig. 1. Show your working.

The procedure was repeated at the same temperature in the presence of a competitive inhibitor of trypsin.

Predict the results that will be obtained using the competitive inhibitor.

Describe how your prediction for part (b) would be different if a non-competitive inhibitor was used rather than a competitive inhibitor.

The investigation was extended to compare the initial reaction rates of trypsin obtained from different species of animals. 

Suggest two advantages of calculating the initial reaction rates of enzyme catalysed reactions here rather than the reaction rates at another point during the experiment.

Researchers immobilised an amylase enzyme in alginate beads. They investigated the effects of temperature on the activity of the immobilised amylase compared with amylase that was free in solution.

The results for this investigation are shown in Fig. 1.

Fig. 1

Compare the effects of temperature on the activity of immobilised and free amylase shown in Fig. 1.

When the researchers immobilised amylase they had to ensure that the alginate beads were all the same size.

Suggest and explain one reason why using different sized alginate beads would affect the activity of immobilised amylase.

State one variable other than bead size that the researchers should keep constant in this investigation.

[1]

Explain your answer to part (i).

[1]

State three advantages of using immobilised enzymes in industrial processes.

Fig. 1 shows the disaccharide lactose, which is found in milk.

Fig. 1

Name the type of bond that joins the two monosaccharides in lactose.

The enzyme lactase catalyses the breakage of the bond between the two monosaccharides in lactose.

(i)

Name the type of reaction that breaks this bond.

[1]

(ii)

Some people do not produce the enzyme lactase, so cannot digest lactose.

The presence of lactose in the lumen of the intestine reduces the volume of water absorbed into the blood, resulting in diarrhoea.

Suggest why the presence of lactose in the intestine reduces the volume of water absorbed.

[2]

Enzymes, such as lactase, are often immobilised for use in the food industry.

A scientist carried out an investigation to determine the effects of temperature on the activity of lactase when it was immobilised and when it was free in solution.

The scientist produced alginate beads containing lactase for use in this investigation. The beads varied in size. The scientist selected small beads for the investigation and put them into a glass column.

(i)

Suggest the advantage of using small beads rather than large beads.

[2]

(ii)

Fig. 2 shows the results of the investigation to determine the effects of temperature on the activity of lactase when it was immobilised, I, and when it was free in solution, F.

Fig. 2

With reference to Fig. 2, compare the effect of temperature on the activity of immobilised lactase, I, and lactase free in solution, F.

Table 1 provides information about the enzymes carbonic anhydrase and penicillinase.

Table 1

Identify the enzyme that has the highest affinity for its substrate.

[1]

(ii)

Give a reason for your answer to part (i).

[1]

Hydrogen peroxide is broken down by the enzyme catalase.

A student investigated the initial rates of reaction for seven different concentrations of hydrogen peroxide. The results of this investigation are represented by line A in Fig. 1.

The investigation was repeated after adding copper ions to the different concentrations of hydrogen peroxide. The results of this investigation are represented by line B in Fig. 1.

Fig. 1

With reference to Fig. 1, suggest an explanation for the effect of copper ions on the action of catalase.

Calculate the K_m value for catalase in the absence of copper ions, using Fig. 1. 

Describe the effect that a competitive inhibitor would have on the affinity of an enzyme for its substrate.

Neutrase® is an enzyme that is used to hydrolyse proteins in solution. When the enzyme is mixed with a 2% protein solution the reaction mixture changes from white to colourless.

A student carried out an experiment to find the effect of copper sulfate and potassium sulfate on the activity of Neutrase®.

The student made four reaction mixtures in test tubes A to D. Test tubes A to C contained equal volumes of protein solution and 0.1 cm³ of solutions of copper sulfate or potassium sulfate. Test tube D contained the same volume of protein solution and 0.1 cm³ of water.

0.5 cm³ of a 1% Neutrase® solution was added to test tube A and immediately placed into a colorimeter. The colorimeter was used to measure the intensity of light that is absorbed by the solution (absorbance) over 100 seconds. The procedure was repeated with the other reaction mixtures, B, C and D.

The results are shown in Fig. 1.

Fig. 1

With reference to Fig. 1:

• Describe the effects of copper sulfate solution and potassium sulfate solution on the activity of Neutrase®
• Suggest explanations for the effects that you have described.

Neutrase® can be immobilised in alginate. Immobilised Neutrase® is used in the food industry to produce foods with high nutritional content.

Explain the advantages of using immobilised enzymes, such as Neutrase®, compared with using the same enzymes free in solution.

The unicellular fungus Kluyveromyces lactis is found in dairy products. It is a safe microorganism to culture for the extraction of the enzyme lactase.

Lactase catalyses the breakdown of lactose, a sugar found in milk.

The reaction catalysed by lactase is summarised in Fig. 1.

Fig. 1

Describe the reaction that is catalysed by lactase. Use Fig. 1 to help you.

In your answer, identify Y and product Z.

On a commercial scale, immobilised lactase can be used to produce lactose-free milk.

One of the products of the reaction shown in Fig. 1 acts as an inhibitor of lactase. This is an example of product inhibition.

(i)

Explain why product inhibition is useful in K. lactis when lactase is acting as an intracellular enzyme, but can be a disadvantage when extracted lactase is used free in solution for the production of lactose-free milk.

[2]

(ii)

Suggest how using immobilised lactase for the production of lactose-free milk helps to reduce the problem of product inhibition.

[1]

(iii)

The first large-scale production of lactose-free milk with an immobilised enzyme used lactase trapped in cellulose triacetate fibres.

Suggest one feature of cellulose triacetate that makes it useful as an immobilising material.

When developing an enzyme-catalysed reaction for use in industry, the progress of the reaction is studied.

Outline how the progress of an enzyme-catalysed reaction can be investigated experimentally.

The enzyme catalase catalyses the following reaction:

H₂O₂ → O₂ + H₂O

A student studied the action of catalase by measuring the volume of oxygen released from the reaction solution using a gas syringe. They recorded the volume of oxygen every 60 seconds over 15 minutes. 

The results of the experiment are shown in Fig. 1 below:

Fig. 1

Calculate the initial rate of reaction shown in Fig. 1. 

The student wanted to investigate the effect of temperature on the rate of reaction of catalase. They did so by repeating the experiment using water baths kept at 20 °C, 30 °C, 40 °C, 50 °C, and 60 °C.

The data from Fig. 1 was taken from the experiment carried out at 30°C. 

Sketch a line onto the Fig. 1 graph to predict the outcome of the experiment at 60 °C.

[2]

Explain the shape of your line from part (i).

[2]

State three factors that the student would need to consider when designing the experiment described in (a) and (b) to ensure valid results.

Catalase is an enzyme found in human body cells, such as liver cells, and plays an important role in metabolism. 

Predict what you would expect the student's results to show about the effect of temperature on catalase activity.

Organic waste materials, such as vomit or urine, can cause stains and unpleasant odours if they get into the fibres of household furnishings. This can be a particular issue for pet owners or parents of very young children. To combat this, many companies have created specialist cleaning chemicals that contain enzymes. 

Explain how these cleaning chemicals carry out their function. 

Vomit contains acidic juices from the inside of the stomach. 

Explain how this could affect the effectiveness of the cleaning chemicals described in part (a).

[3]

(ii)

Suggest how the chemical companies could improve the efficiency of these chemicals under the circumstances described in part (i).

[1]

It is important that the cleaning chemicals described in part (a) are non-toxic. 

Suggest why this might be important to the consumer, and why the companies are able to make this claim. 

The cleaning products can be sold in the form of a powder that can be sprinkled directly onto the stain, or dissolved in warm water before being sprayed onto the stain. 

Explain the potential benefits of dissolving the powder in warm water before it is applied to the stain.