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End product inhibition of Enzymes.

  • /
  • Additional HL/
  • HL Metabolism Activities for Learning/
  • End product inhibition of Enzymes.

Following a quick review of enzyme inhibition students complete a few structured notes leading to an experiment with enzymes and inhibitors. Students collect data and produce graphs for analysis. A third activity summarises the way end product inhibition can control enzyme activity and maintain a concentration of product in a cell.

Lesson Description

Guiding Questions

  • How can we stop enzyme-catalysed chemical reactions?
  • How are non-competitive inhibitors different from competitive inhibitors?
  • How do cells control enzymes?

Activity 1 - Some details about non-competitive inhibitors

Watch the short animation which recaps competitive and non-competitive inhibitors

Complete notes about competitive and noncompetitive inhibitors using the simple enzyme inhibition notes worksheet below.

Activity 2 - An experiment to illustrate enzyme inhibition

Carry out one of the following experiments on enzyme inhibition. 

 

Enzyme | Biology Simulations

Enzymes are proteins that increase the rate of biological reactions. This simulation can be used to test how factors such as temperature, pH, and concentrations affect the reaction rates of two different...

 Biology Simulations
 

Catalase Inhibition Lab

Data Purpose The undiluted CuSO4 Run 1: ERROR The catalase was not functioning properly and was replaced with a new sample of catalse Our 10 mM stock Copper sulfate was used as the inhibitor. This was...

 prezi.com
 

The effect of phosphate on the enzyme phosphatase | STEM

This investigation involves an acid phosphatase extracted from germinating mung beans (beansprouts). and an artificial substrate, phenolphthalein phosphate The phosphate inhibits the enzyme.

 www.stem.org.uk

Data Analysis

Analyse the following data from an experiment on enzymes and inhibitors to try to find out if the inhibitors are competitive or non-competitive inhibitors? This is model data, but will help to understand graphs about reaction rates and the effect inhibitors have on enzyme activity.

There are many possible ways to analyse the data, but one example is found on the Enzyme data - model analysis page

Activity 3 - End product inhibition

Look at the diagram and try the activity below.

Describe how end product inhibition can maintain a constant concentration of a metabolic product using the statements below. The statements below are in the wrong order (except the first and last). Printable list of statements

Rearrange these statements to explain how end product inhibition works?

  • At the beginning there is no isoleucine - so there is no inhibition.
    .
  • As the cell uses up isoleucine to build proteins (it's an amino acid!) its concentration falls.
  • The enzymes in the pathway produce isoleucine rapidly
  • The concentration in isoleucine increases
  • The rate of activity of all the enzymes in the pathway slows down because they have a low concentration of substrate molecules.
  • The rate of production of isoleucine slows down.
  • The isoleucine inhibits some molecules of the first enzyme in the pathway and so slows the activity of this enzyme.
    .
  • Inhibition reduces and the rate of the pathway increases because the concentration of isoleucine was lower.

Click the eye icon to display a model answer.

Model answer statements to explain how end product inhibition works?

  • At the beginning there is no isoleucine - so there is no inhibition.
  • The enzymes in the pathway produce isoleucine rapidly
  • The concentration in isoleucine increases
  • The isoleucine inhibits some molecules of the first enzyme in the pathway and so slows the activity of this enzyme.
  • The rate of activity of all the enzymes in the pathway slows down because they have a low concentration of substrate molecules.
  • The rate of production of isoleucine slows down.
  • As the cell uses up isoleucine to build proteins (it's an amino acid!) its concentration falls.
  • Inhibition reduces and the rate of the pathway increases because the concentration of isoleucine was lower.

Teacher's notes

These three activities aim to consolidate student understanding of enzyme inhibition, and end product inhibition.

The first activity is a simple review task, with the help of a very short 1 minute video. The worksheet may help students to keep structured notes. The last question on the worksheet leads into the second activity.

The second activity could be an wet lab experiment. Ideally students could collect their own data and analyse this to identify the type of inhibitor. If the data are not reliable there is also a set of data in this activity which could provide training for students before they do their own analysis or could be a separate activity on its own. The data is a Google spreadsheet and can be copied to enable editing, otherwise the data can be copied and pasted into excel, logger pro or another spreadsheet software. Of course it could be used to plot graphs by hand too.

There is an interesting enzyme an inhibition lab from SSERC in Scotland - Competitive inhibition of β-galactosidase.

Activity three could be a whole class activity or a homework task. Students use a set of seven phrases to describe end product inhibition of the isoleucine metabolic pathway

Resources that didn't make it - here but might be good to use another time

There are some good explanations on these animations about enzyme inhibition, but reversible and non-reversible inhibition is mentioned a lot in them. This is not a concept required for IB.

Simulating enzyme reactions using plastic beads can be a useful activity for some students. This Word document by Mark Little of Broomfield School, Colorado includes several easily adaptable activities using beads to simulate enzyme reactions. One of the activities includes illustrating competitive inhibition of enzyme by bouncing a tennis ball, (holding a tennis ball might be enough of an inhibition and less chaotic in a room full of beads!). Perhaps to illustrate non-competitive inhibition students could slightly change the shape of their hands by wearing gloves or socks. It would be great to adapt this to illustrate end-product inhibition if a group of students modelled a metabolic pathway and whenever there were too many molecules of end product the first student had to wear gloves.

Beads can be found in many places, but this the-beadshop will ship worldwide