Activation energy and enzyme pathways

Image; public domain from wiki commonsStudents are introduced to a simple metabolic pathway consisting of a chain of enzyme-catalysed reactions leading to the Kreb's cycle which is a cycle of enzyme catalysed reactions.  The method of enzymes to lower the activation energy is explained through an animation and there are some questions for students to answer.

Lesson Description

Guiding Questions

  • What do we mean by "metabolism"?
  • When chemicals collide with more energy than the "activation energy" a reaction happens. How do enzymes change this activation energy to speed up reaction rates?
  • If each enzyme is substrate specific how can enzymes perform complex reactions like DNA replication?

Activity 1 - What is metabolism?

Look at this diagram which summarise the enzyme catalysed reactions that break down alcohol into water and carbon dioxide.



Which enzyme has the product acetaldehyde?

Which enzyme has the substrate acetaldehyde?

How do the enzymes link together to form a metabolic pathway?

Model answers

Which enzyme has the product acetaldehyde?

alcohol dehydrogenase

Which enzyme has the substrate acetaldehyde?

acetaldehyde dehydrogenase

How do the enzymes link together to form a metabolic pathway?

The first enzyme produces the substrate of the second enzyme and so on.

Each enzyme catalyses one reaction in a chain of reactions.


Activity 2 - Enzymes and activation energy

For a short summary of how enzymes work watch this animated explanation of enzymes

Watch this animation of how enzymes lower the activation energy (select the "Overview")

 Then answer the questions on  the enzyme activation energy worksheet shown below​.

Activity 3 - Extension - Brows a database of the complete human metabolism

Click this link to take you to the website.  This is a free open source, peer reviewed knowledge base about human metabolism.  Beware the complexity of this might blow your mind!

Here is a simple preview .... focused on glycolysis.

Teacher's notes

This is meant to be a simple introduction to metabolic pathways.  The alcohol metabolism is important in the next topic so to introduce it here will help later.

Enzymes are covered in topic 2.6 and in the digestion section of topic 6.  The details covered here are the extra HL details about activation energy.  There are a couple of links included for revision.

The third activity is really just an invitation to browse a database on human metabolism.

There is a nice clear explanation of energy in chemical reactions including enzymes and activation energy in this video

There are model answers on the page -  see link in the left hand menu.

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