1. Enzymes

2. Most reactions take place in a number of steps which need to be carefully controlled if the cell is to function properly
Enzymes are the most important controllers of cellular reactions

3. Catalysts
**Catalysts speed up reactions without themselves being changed in the reaction
Enzymes are catalysts made of protein. They speed up a reaction without being used up themselves in the reaction
Because enzymes are made in living things they are called biological or organic catalysts

4. Proteins are made when amino acids join together
The function of a protein is decided not only by the sequence of amino acids but also by the way the protein folds
Most enzymes are globular proteins

5. Learning Check What is an Enzyme? What are catalysts?
To what group of bio-molecules do enzymes belong?

6. How enzymes work
Enzymes are not flat they have a 3D structure

7. Each enzyme has its own specific shape that will only “fit” the molecule that the enzyme is designed to work on
If the enzyme that breaks starch into glucose meets a fat molecule it will not fit it and will not be able to work on it

8. Learning Check Why is the shape of an enzyme important?
Are enzymes flat, 3D or 2D in shape?

9. Enzyme Action The substance that an enzyme acts on is its substrate
The substance(s) that the enzyme forms is called the product(s)

10. A Catabolic enzyme Amylase converts starch to maltose
Catabolic because it breaks a big molecule into a smaller one
It is produced by saliva glands in mouth and by the pancreas

11. An Anabolic Enzyme DNA Polymerase forms and repairs DNA
Anabolic because it coverts simpler molecules into more complex
molecules
Found in almost all living things

12. Consider This
Amylase is an enzyme found in saliva. It breaks starch molecules into smaller maltose molecules
What is the substrate?
What is the product?
Will amylase break fats into fatty acids + glycerol? Why?
Is this an example of a catabolic or an anabolic reaction? Why?

13. And This
DNA Polymerase is an enzyme that builds DNA using tiny molecules in our cells
What is the substrate?
What is the product?
Will amylase build keratin out of peptides? Why?
Is this an example of a catabolic or an anabolic reaction? Why?

14. Enzyme/Substrate Complex
Enzymes work because they have the correct shape to fit the substrate
They have a complex 3 dimensional shape to fit the substrate
When enzymes and their substrates meet and come together they form an Enzyme/Substrate complex

16. Learning Check What is meant by a substrate?
What is the unit formed when an enzyme combines with its substrate called?
Give an example of an anabolic reaction
Give an example of a catabolic reaction

17. Enzyme Reactions are reversible
Like a key can open or close a lock enzymes can make reactions go in either direction

18. In the following example the enzyme can break molecule X into Y+Z but it can also combine Y+Z to form X
X Y + Z

19. Learning Check
Can enzyme reactions be reversed?

20. Naming Enzymes
Enzymes are named by adding the suffix ase to the name of their substrate
Eg.
Enzyme that acts on Amylose (starch) is called amylase
Enzymes that act on proteins are called proteases

21. Learning Check Can you think of a name for enzymes that act on Lipids?
Amazingly enough they are called Lipases!

22. Inhibitors Inhibitors attach to enzymes and destroy their shape
When this happens the enzymes are said to be denatured

23. Nerve Gases
The nerve gases we hear of terrorists using are often inhibitors that attach to enzymes involved in our nerve transmissions

24. Poisoning people the old fashioned way!
Cyanide denatures an enzyme involved in respiration

25. Beneficial Inhibitors
Insecticides affect enzymes in insects causing their death
Drugs can affect enzymes involved in pain causing the pain to stop
Antibiotics can affect enzymes in bacteria causing the bacteria to die

26. Learning Check What is an inhibitor? How do inhibitors work?
Can you give an example of a harmful inhibitor?
Can you give an example of a beneficial inhibitor?

27. Enzymes at work! Enzymes work best in certain conditions
Factors that affect enzymes include
Temperature pH
Substrate concentration
Enzyme concentration
We will be examining these in experiments

28. Temperature
At very low temperatures ice forms, liquids become solids and enzymes can’t work
As temperature increases molecules start to move and bump into each other causing the rate of reaction to increase

29. Human enzymes work best at body temperature (37°C)
Plant Enzymes work best at °C
Above certain temperatures enzymes start to lose their shape the rate of reaction falls
When the shape is fully lost the enzyme is said to be denatured this is usually a permanent condition

30. pH
pH scale goes from 0 -14
0-7 is acidic
7-14 is basic (or alkaline)

31. Enzymes work over a very narrow pH
Most enzymes work at pH 6-8
Outside this they lose shape and get denatured
The optimum or best ph is usually pH 7

32. An Exception! Is our stomach acid or basic?
Do you think there are enzymes in our stomach?
Pepsin is an enzyme in the stomach that works best at pH 2!

33. Learning Check What factors affect enzyme action?
What is the best temperature for (a) human enzymes and (b) plant enzymes?
What is meant by pH?
Do enzymes work over a narrow or wide pH range?

34. Immobilised Enzymes
Bio-processing is the use of enzyme controlled reactions to produce a product
Bio-processing can be used to produce a vast range of products such as cheeses, beer, antibiotics, vaccines, methane gas, food flavours, vitamins and perfumes

35. Traditionally micro-organisms such as bacteria and yeast were used but since the 1900’s and especially since the 1950’s enzymes are being used

36. If enzymes are used freely dissolved in a vessel it can be very wasteful as they are lost at the end of the process
To prevent this problem enzymes are often immobilised or fixed
This means they are attached to each other or an inert substance and can be used repeatedly

37. Learning Check What is bio-processing?
What type of organisms are uasually used in bio-processing?
Why is bio-processing advantageous?

38. How to immobilise enzymes
Physical methods
Adsorption where enzymes are physically attached to inactive supports such as glass beads or ceramics
Enclosed by a membrane when enzymes are kept within a membrane
Trapped in a gel, sodium alginate is commonly used this allows substrates in and products out

39. Chemical Methods
Bonded to a support enzymes chemically bonded to a support such as glass beads or ceramics
Bonded to each other Enzymes are chemically bonded to each other

40. Advantages of Immobilised Enzymes
Efficiency of enzyme is not affected
Immobilised enzymes can be easily recovered from the product so you can get a pure sample of product easily
Immobilised enzymes can be reused this cuts costs
Enzymes frequently become more stable when immobilised

41. Uses of Immobilised Enzymes
Immobilised glucose isomerase converts glucose to fructose which is used to sweeten drinks
Penicillin acylase changes the structure of penicillin to make more antibiotics that will fight a wider range of bacteria
Lactase converts lactose to sweeter sugars glucose and galactose which are then used by food manufacturers

42. Learning check Describe 2 physical methods of immobilising enzymes
Describe 2 chemical methods of immobilising enzymes
What are the advantages of immobilising enzymes?
Can you name 3 things immobilised enzymes are used for?

43. Syllabus Can you....... Define the term: enzymes
State the nature, folded shape & functions of enzymes.
Explain the role of enzymes in plants and animals including role in metabolism
Explain the effects of pH & temperature on enzyme activity.
State the procedure and advantages of Bio-processing.
State the use of Bio-processing.

44. Enzymes Extended Study

45. The Active Site
The Active site is the part of the enzyme that combines with the substrate

46. Contrary to belief the active site is not a rigid shape that is fixed to fit the substrate
*When the substrate enters the active site it causes it to change shape slightly
The enzyme then fits more precisely around the substrate this is known as the Induced Fit model of enzyme action

48. The Bean Bag Theory!
The induced fit model can be compared to the way a bean bag will adapt to fit snugly around our body shape when we sit in it

49. Mechanism of Enzyme action (Induced fit model)
See p. 103 Fig 10.1
The substrate combines with the active site of the enzyme
Active Site
Substrate
Enzyme

50. 2. The active site is induced or caused to change shape slightly
Enzyme
Substrate

51. 3. The substrate and enzyme form an enzyme substrate complex
The bonds in the substrate are altered so that the substrate changes into the products
Substrate changed to products which are released
Enzyme Substrate complex

52. 4. The products leave the active site
4. The products leave the active site. The active site returns to its original shape and is ready for a new substrate molecule
Products
Active Site
New Substrate
Enzyme

53. Learning Check
Can you describe how enzymes and their substrates fit together?
What is this model of enzyme action called?
Can the enzyme work on more substrate once the products have been formed?

54. Optimum Conditions
Optimum temperature refers to the temperature at which the enzyme will work best
Optimum pH refers to the pH at which the enzyme will work best and so on
What do you think body enzyme’s optimum temperature is?

55. Denaturation
When most proteins are heated above 40⁰C or treated with certain chemicals or radiation they will gradually lose their 3 dimensional shape
This means they will not be able to form the enzyme / substrate complex
How does heat denature an enzyme?
Can you give an example of this?

56. Learning Check What is meant by Optimum?
What do you think the optimum temperature is for most body enzymes is?

57. Syllabus Can you?.....
Explain the active site theory to examine enzyme function & specificity.
Explain the term optimum activity with reference to temperature.
Explain the nature of heat denaturation