Enzymes

The importance of enzymes is the underlying theme of this topic at A level, in terms of their ability to catalyse a wide range of intracellular and extracellular reactions which can affect the functions from the cellular level to whole organism level. Knowledge of the function of enzymes and the factors which affect their action has led not only to a greater understanding of biological processes, but also to the use of enzymes in a wide range of industrial processes. Students will be required to give examples of enzymes that catalyse intracellular and extra cellular reactions.

It is also a requirement that students not only understand the model of enzyme action, but have an appreciation of how this has changed over time from the lock and key to the induced fit model. Students will need to be able to explain the lowering of activation energy, the need for coenzymes in some enzyme-controlled reactions and the possible mechanisms of enzyme inhibition.

There are a plethora of experiments that can be included within this topic, practical investigations into the effects of PH, temperature, enzyme concentration and substrate concentration on enzyme activities are all possibilities. Students need to be able to confidently interpret graphical data from such experiments.

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or other recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.

Jelly Liquidiser

Quality AssuredCategory:SciencePublisher:National STEM Learning Centre and Network

This short video would make an interesting start to an A level lesson on Enzymes. The video shows how pineapple, when added to a bowl of jelly is able to liquify the jelly, due to the enzyme action in the fruit which breaks down the gelatin in the jelly.

It would be possible to add in extra questions to the video to provide A level challenge, such as why does the pineapple have to be fresh? Why couldn't tinned pineapple be used? What enzyme does the Pineapple contain? When we say the gelatin is being broken down, what do we mean?

Students could quickly carry out this experiment using a) fresh pineapple, b) tinned pineapple and c) another fruit to compare and contrast the results and then write up an A Level standard explanation of what is happening.

Enzyme Activity in Fruits and Vegetables

Quality AssuredCategory:SciencePublisher:Science & Plants for Schools (SAPS)

 

This is one of three practicals listed here from Science & Plants for Schools (SAPS). These materials give a range of suggested activities that investigate enzyme activity in ripening fruit. These include:

  • the changes in enzyme activity during ripening and storage
  • the activity of the same enzyme in different species
  • the loss of an enzyme substrate (such as pectin or starch) during the ripening process
  • the appearance of an enzyme product (such as glucose or galactose) during the ripening process

All of these are useful for students to understand the action of enzymes in situ. Small groups of students could be tasked with completing a different assay each and then be prepared to present their methodology, results and interpretation of the results to the rest of the class.

Investigating the Effect of Temperature on Lipase Activity

This practical investigation is one of several protocols available to fulfil A level requirements on the effects of factors on enzyme activity. It provides a suitable level of challenge for A level students in terms of organisation of practical work, practical skills and on the presentation and interpretation of results.

This particular investigation considers how a solution of milk, lipase and phenolphthalein will change from pink to colourless as the fat in milk is broken down to form fatty acids (and glycerol) thus reducing the pH to below 8.3. The time taken for this reaction to occur is affected by temperature.

Teachers should make use of the student sheet provided for this investigation (see bottom of the page). A level students should produce the graphs as indicated in steps l and m. (coming up with the correct scale often proves a challenge!). Students can also answer the questions provided (remember not to give out the answer sheet, which is the third page).

There are other practicals on this site that could also be used to investigate effect of pH or the effect of concentration.

Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts

One of the A level required practicals is an investigation into the effect of a named variable on the rate of an enzyme-controlled reaction. 

CLEAPSS have a modified method suggested by a technician in a Newcastle school which works very well and in a very short time.  There is a video and a  full method.