Enzymes & Metabolism (SL IB Biology)

Certain plants that reproduce sexually contain an enzyme called pyrophosphatase. This enzyme plays a role in ensuring self-incompatibility, which is a mechanism that prevents a plant from fertilising itself. The selective advantage of self-incompatibility is that more cross-breeding can occur within a species, which has long term benefits for evolution and for maintaining a large pool of alleles.

Known volumes of pyrophosphatase and substrate can be mixed in a cuvette with a dye that starts as colourless and develops into a blue colour over time. The rate of colour development can be measured in a colorimeter by measuring the absorbance of light at a wavelength of 620 nm (red light). 

The graph shows the mean rate of reaction of pyrophosphatase measured over five repeats at 20°C.

State why the wavelength of 620 nm was selected for this experimental measurement.

Use the graph from part (a) to calculate the rate of the reaction at 100 seconds. Give your answer in suitable units. 

Predict the effect that a higher enzyme concentration at the start of the experiment would have on the results calculated in part (b).

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Explain your answer in part (i).

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Outline how changes in substrate concentration affects the rate of enzyme action. 

Plan an investigation to determine how changing the temperature of amylase affects the rate of reaction of the digestion of starch to maltose. 

Three rivers in the Scottish Highlands were polluted with copper, which affected the aquatic wildlife. Scientists were provided with one dead brown trout, Salmo trutta, from each of the rivers.

Scientists were unable to take a direct measurement of the copper ion concentration in the river.

Using the information provided in part (b), suggest the dependent, independent and control variables of an experiment using the fish tissue to compare the copper ion pollution in the three rivers.

Scientists were trying to investigate the rate of reaction of alcohol dehydrogenase by measuring the quantity of product, methanoic acid, produced over time, with a fixed quantity of methanol added at the start. 

The graph below shows their results. 

Use the graph below to calculate the rate of reaction of alcohol dehydrogenase after 3 minutes. 

Lipase is an enzyme that breaks down lipids. The diagram below shows an experiment set up by a teacher to investigate the effect of lipase concentration on the hydrolysis of lipids.

The pH of beaker B is measured for 3 minutes at the start of the experiment. Beaker A containing lipase solution is added to beaker B. The data logger recorded the change in pH over the next 5 minutes.

State, with a reason, the predicted change in pH after the lipase has been added. 

State two variables that must be controlled to carry out the experiment in part (a) accurately and reliably.

For the experiment in part (a), draw a results table that could be used to record the results of the investigation. Your table should include suggested enzyme concentrations, and units should be stated. 

A protease is an enzyme that digests protein. A research scientist isolated protease C from a particular species of bacteria. The researcher investigated the effect of temperature on the rate of hydrolysis of a protein by protease C.  The unprocessed results can be seen in the table below.

Calculate (with appropriate units) the missing details in the table above.   

Draw a graph of the results seen in part (a). Your graph should include an accurate scale and correct axis labels.

Suggest how the research scientist controlled the pH throughout the experiment.

Explain the aspect of enzyme and substrate structure that enables successful catalysis of a biochemical reaction.

The sketch graph below shows how the rate of an enzyme-catalysed reaction varies for two separate independent variables. For curve A the independent variable is the concentration of enzyme.

Identify the independent variable for Curve B.

The sketch graph below shows how the rate of an enzyme-catalysed reaction varies as temperature changes.

Explain the rates of reaction at positions A, B, and C on the curve. 

The sketch graph below shows the effects of varying the level of the independent variable, X, on the rate of an enzyme-controlled reaction. Lines A, B, and C represent three different independent variables which could be X. 

An experiment was set up to investigate the effect of temperature on an enzyme-catalysed reaction in which the reaction mixture changes from clear-colourless to clear-dark blue as the reaction progresses.

Describe:

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.

The graph below shows the progress of this reaction when it is carried out at 25 °C.

Calculate the initial rate of the reaction in the graph. Show your working.

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

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.

The Plasmodium falciparum parasite depends on glycolysis for its survival, particularly the uptake of glucose from its host cells which is mediated by hexokinase.

The scientists investigated the action of hexokinase within Plasmodium falciparum.  They tagged hexokinase with two different potential drugs that inhibit its action. Their results are shown in the graph below.

Describe how to calculate the rate of reaction from the graph.

The scientists concluded that drug 1 was less effective than drug 2.

Evaluate this conclusion.

Distinguish between an enzyme catalysed reaction and a non enzymatic reaction.