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Cambridge Pre-U Biology - 1.4 Enzymes


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This is part of the PowerPoint that covers section 1.4 in the Cambridge Pre-U Biology course. The full PowerPoint covers the following topics: Enzyme structure and function, enzyme kinetics and immobilised enzymes.

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Cambridge Pre-U Biology - 1.4 Enzymes

  1. 1. MAKING SENSE OF Icons CC – The Pink Group Copyright©2017HenryExham
  2. 2. Copyright © 2016 Henry Exham • The reactions in cells necessary for life need to happen fast! • The temperature that most cells are kept at means that the reactions naturally go quite slowly. • Enzymes speed up reactions without being used up themselves. • They are biological catalysts. 2
  3. 3. MAKING SENSE OFMAKING SENSE OF Structure and function of enzymes Enzyme kinetics Commercial uses of enzymes 3
  4. 4. Copyright © 2016 Henry Exham a) Discuss why enzymes are essential to life. b) Describe the structure and properties of enzymes including their role as catalysts in catabolic and anabolic reactions (both intracellular and extracellular). c) Explain the specificity of enzymes and the induced- fit mode of action. 4
  5. 5. Copyright © 2016 Henry Exham • Enzymes can speed up a reaction by up to 1021 times faster! 5
  6. 6. Copyright © 2016 Henry Exham • The most common enzyme on the planet is Ribulose- 1,5-bisphosphate carboxylase oxygenase better known as . • It is used in the process of photosynthesis and you will learn more about it when you study that topic later on in the course. 6
  7. 7. Copyright © 2016 Henry Exham • Enzymes are globular proteins. • Most of their names end in –ase. • They have a very specific shape because of the bonding as explained in the protein structure section of the course. • Because of this they have a high specificity. • This means they usually only catalyse one specific reaction. 7 Substrate
  8. 8. Copyright © 2016 Henry Exham • The active site is a very small part of the whole enzyme. • It is formed by the proteins primary structure. • The substrate binds by forming weak non-covalent interactions with the R-groups of the active site’s amino acids. By Thomas Shafee - Own work, CC BY 4.0,
  9. 9. Copyright © 2016 Henry Exham • Enzymes can either help break something down (catabolic reaction) or build it up (anabolic reaction). • They can work inside cells (intracellular enzymes) or outside cells (extracellular enzymes). – Intracellular enzymes that you have seen in this course so far include helicase and DNA polymerase. – Extracellular enzymes that you will be familiar with are the digestive enzymes such as lipase and amylase. 9
  10. 10. Copyright © 2016 Henry Exham • As already mentioned enzymes speed up the rate of reactions. • For a reaction to occur there has to be enough energy, we call this the activation energy. • This is shown on the graph. 10 Reactants Products Reaction Time Energy Activation energy
  11. 11. Copyright © 2016 Henry Exham • Enzymes work by binding to the reactants at the beginning and lowering the activation energy required to make the products. • This is shown on the graph by the red line. 11 Reactants Products Reaction TimeEnergy Activation energy with enzyme
  12. 12. Copyright © 2016 Henry Exham 12 METABOLIC REACTIONS ANABOLIC (Build up) CATABOLIC (Break down) Energy Small molecules Large Molecules This is an ENDERGONIC reaction as energy is required Energy Small molecules Large Molecules This is an EXERGONIC reaction as energy is released Both types of metabolic reaction rely on enzymes
  13. 13. Copyright © 2016 Henry Exham • Cell reactions are all reversible (they can work in both directions). • If a reaction like this happened outside the body it would just reach equilibrium where formation of products is equal to formation of substrates. • However, in a cell you are always adding new reactants or removing products so it never reaches the state of equilibrium.
  14. 14. Copyright © 2016 Henry Exham • We know that they must bind to the substrate to form an enzyme/substrate complex for the reaction to take place. • But there are two hypothesis as to how this exactly works. 14 ‘Lock-and-key’ Induced fit
  15. 15. Copyright © 2016 Henry Exham • There is an area on the enzyme called the active site. • It has a very specific rigid shape that only one substrate will exactly fit into. • This model explains the specificity of enzymes well. • For a long time this was the only theory of how enzymes worked. 15 ‘Lock-and-key’
  16. 16. Copyright © 2016 Henry Exham 16 Products form and leave active site Reaction occurs Substrate enters active site An enzyme-substrate complex forms 1 2 3 4 ‘Lock-and-key’
  17. 17. Copyright © 2016 Henry Exham To download the whole presentation visit
  18. 18. This PowerPoint is protected under copyright. It is designed for educational use. Either personal study or to be presented to a class. It may be edited or duplicated for these purposes only. It must not be shared or distributed online in any format. Some images used are under a separate creative commons license, these are clearly marked. Copyright © 2016 Henry Exham Brought to you by