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Enzymes
Learning Objectives
At the end of the lessons, students should be able to:
• Define what is an enzyme
• Explain enzyme act...
What are Enzymes??
*Take note of what are enzymes and their functions
What are Enzymes?
•Biological catalyst made of protein
•Speed up chemical reactions in living
organisms without themselves...
Some important Terminologies
Substrates (Reactants)
• Substances on which enzymes act on
• Eg: Starch (substrate) which sa...
Some important Terminologies
Products
• Substance obtained after an
enzymatic reaction
How does Enzymes work?
Picture this…
Enzymes
Complex molecules Simpler molecules
How does Enzymes work?
Picture this…
Enzymes
Simple molecules Complex molecules
What is needed for the a
chemical reaction...
•To start a chemical reaction, a certain
amount of energy is needed.
•This amount of energy is called
activation energy
Ho...
•Enzymes work by lowering the activation
energy required to start the reaction.
• In this way, the reaction is sped up
How...
Enzymes lowers the activation
energy of chemical reactions
What are the types of Enzyme
Reactions?
Break down complex
substances
Build up complex
substances
Types of Enzyme Reactions
Break down complex molecules into
simpler molecules
• E.g. digestion of maltose to glucose
malta...
Types of Enzyme Reactions
Build up complex molecules from simpler
molecules
• E.g. Glucose  Glycogen
Glycogen
synthase
Gl...
Classification of Enzymes
Type of Enzyme
Carbohydrase
Protease
Lipase
Type of Substrate
Fats/ Lipids
Protein
Carbohydrates...
Properties of Enzymes
1. Speeds up chemical reaction
2. Required in small amounts
3. Specific in action
4. Affected by tem...
1. Enzymes speed up chemical reaction
Properties of Enzymes
• By lowering the activation energy needed to start the
reacti...
2. Enzymes are required in minute amounts
Properties of Enzymes
• Enzymes remain chemically unchanged after a
chemical rea...
3. Enzymes are specific in action
Properties of Enzymes
• One kind of enzyme will catalyse only one kind of
chemical react...
4. Enzymes are affected by temperature
Properties of Enzymes
• Enzymes are made up of proteins
• Enzymes denatures at high...
Effect of Temperature on
Enzyme Reaction
Effect of Temperature on
Enzyme Reaction
A
• Enzymes are inactive at very low temperatures
• Low rate of reaction
Enzymes ...
Effect of Temperature on
Enzyme Reaction
B
• Enzyme activity increases as temperature rises
• Rate of reaction
increases
M...
Effect of Temperature on
Enzyme Reaction
C
• Enzyme activity reaches its maximum rate
• At the optimum
temperature
Most en...
Effect of Temperature on
Enzyme Reaction
D
• Enzyme rate of reaction decreases  ZERO
• The enzymes
denatures
The structur...
Illustration: Denaturation
Virtual Lab Experiment
• http://www.mhhe.com/biosci/genbio/virtual_labs/BL_11/BL_11.html
5. Enzymes are affected by pH
Properties of Enzymes
• Enzymes are made up of proteins
• Enzymes denatures at extreme pH
• ...
Effect of pH on
Enzyme Reaction
• Optimum pH:
• The pH value at which the rate of enzyme reaction
is the highest
• Extreme...
Effect of pH on
Enzyme Reaction
Rateofreaction
6. Enzymes catalyse reversible reactions
Properties of Enzymes
• Reactions can proceed in forward and
backward direction
•...
The enzyme & substrate molecules will
combine to form a temporary structure called
enzyme-substrate complex
Some important...
Action of Enzyme
(Build Up Reaction)
enzyme
substrate
enzyme
product
enzyme-
substrate
complex
Pure
Action of Enzyme
(Break Down Reaction)
enzyme
product
enzyme
substrate
enzyme-
substrate
complex
Pure
Which statement is true of all enzymes?
Micro Ques 1
( D )
A They are denatured at temperatures above 60 oC.
B They are in...
2 ml of amylase solution is added to 5ml of starch solution which is
kept in a water bath maintained at 70 oC. Then the mi...
An enzyme may be inactivated by ___________.
Micro Ques 3
( B )
A removing the products of the reaction as they appear
B b...
MicroQuestion
• Qn1: Enzymes speed up rate of reaction, Highly
specific in their reaction. Remain chemically
unchanged at ...
!! Activity Time !!
Each of you should
get either a KEY or a
LOCK
You have 5 mins to look for the key
that opens your lock!
Lets Reflect!
• What does the lock represent?
• Enzyme
• What does the key represent?
• Substrate
• Where is the active si...
Issues with the
Lock & Key Hypothesis
The lock (enzyme) changes
shape after the reaction
*Enzymes are unchanged
after the ...
Enzymes
In conclusion, enzyme action is specific due to
the shape of the substrate and active site
being complementary to ...
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Enzymes

  1. 1. Enzymes
  2. 2. Learning Objectives At the end of the lessons, students should be able to: • Define what is an enzyme • Explain enzyme action in terms of the ‘lock and key’ hypothesis. • Explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex, lowering of activation energy and enzyme specificity. (PURE) • Investigate and explain the effects of temperature, pH on the rate of enzyme catalysed reactions.
  3. 3. What are Enzymes?? *Take note of what are enzymes and their functions
  4. 4. What are Enzymes? •Biological catalyst made of protein •Speed up chemical reactions in living organisms without themselves being chemically changed at the end of the reactions
  5. 5. Some important Terminologies Substrates (Reactants) • Substances on which enzymes act on • Eg: Starch (substrate) which salivary amylase acts on Active Site • Depressions on the surface of an enzyme molecule where the substrate can fit
  6. 6. Some important Terminologies Products • Substance obtained after an enzymatic reaction
  7. 7. How does Enzymes work? Picture this… Enzymes Complex molecules Simpler molecules
  8. 8. How does Enzymes work? Picture this… Enzymes Simple molecules Complex molecules What is needed for the a chemical reaction to take place?
  9. 9. •To start a chemical reaction, a certain amount of energy is needed. •This amount of energy is called activation energy How does Enzymes work? Pg 7
  10. 10. •Enzymes work by lowering the activation energy required to start the reaction. • In this way, the reaction is sped up How does Enzymes work? Pg 7
  11. 11. Enzymes lowers the activation energy of chemical reactions
  12. 12. What are the types of Enzyme Reactions? Break down complex substances Build up complex substances
  13. 13. Types of Enzyme Reactions Break down complex molecules into simpler molecules • E.g. digestion of maltose to glucose maltase
  14. 14. Types of Enzyme Reactions Build up complex molecules from simpler molecules • E.g. Glucose  Glycogen Glycogen synthase GlycogenGlucose molecules
  15. 15. Classification of Enzymes Type of Enzyme Carbohydrase Protease Lipase Type of Substrate Fats/ Lipids Protein Carbohydrates Example of Enzyme Maltase Pepsin Intestinal Lipase
  16. 16. Properties of Enzymes 1. Speeds up chemical reaction 2. Required in small amounts 3. Specific in action 4. Affected by temperature 5. Affected by pH 6. Catalyse reversible reactions
  17. 17. 1. Enzymes speed up chemical reaction Properties of Enzymes • By lowering the activation energy needed to start the reaction
  18. 18. 2. Enzymes are required in minute amounts Properties of Enzymes • Enzymes remain chemically unchanged after a chemical reaction • Can be reused again & again
  19. 19. 3. Enzymes are specific in action Properties of Enzymes • One kind of enzyme will catalyse only one kind of chemical reaction • Substrate specific (Lock & Key hypothesis)
  20. 20. 4. Enzymes are affected by temperature Properties of Enzymes • Enzymes are made up of proteins • Enzymes denatures at high temperatures • Enzymes are inactive at low temperatures
  21. 21. Effect of Temperature on Enzyme Reaction
  22. 22. Effect of Temperature on Enzyme Reaction A • Enzymes are inactive at very low temperatures • Low rate of reaction Enzymes are not destroyed at very low temperatures
  23. 23. Effect of Temperature on Enzyme Reaction B • Enzyme activity increases as temperature rises • Rate of reaction increases Molecules moves faster in higher temperatures, substrate & enzyme will collide more often
  24. 24. Effect of Temperature on Enzyme Reaction C • Enzyme activity reaches its maximum rate • At the optimum temperature Most enzymes have an optimum temp of 40 oC
  25. 25. Effect of Temperature on Enzyme Reaction D • Enzyme rate of reaction decreases  ZERO • The enzymes denatures The structure of the active site changes  substrate cannot bind  rxn decreases
  26. 26. Illustration: Denaturation
  27. 27. Virtual Lab Experiment • http://www.mhhe.com/biosci/genbio/virtual_labs/BL_11/BL_11.html
  28. 28. 5. Enzymes are affected by pH Properties of Enzymes • Enzymes are made up of proteins • Enzymes denatures at extreme pH • Acidic / Alkaline
  29. 29. Effect of pH on Enzyme Reaction • Optimum pH: • The pH value at which the rate of enzyme reaction is the highest • Extreme pH: • Denatures enzymes • Changes the structure of the active site
  30. 30. Effect of pH on Enzyme Reaction Rateofreaction
  31. 31. 6. Enzymes catalyse reversible reactions Properties of Enzymes • Reactions can proceed in forward and backward direction • Eg: CO2 H2CO3H2O+ carbonic anhydrase WaterCarbon dioxide Carbonic acid
  32. 32. The enzyme & substrate molecules will combine to form a temporary structure called enzyme-substrate complex Some important Terminologies
  33. 33. Action of Enzyme (Build Up Reaction) enzyme substrate enzyme product enzyme- substrate complex Pure
  34. 34. Action of Enzyme (Break Down Reaction) enzyme product enzyme substrate enzyme- substrate complex Pure
  35. 35. Which statement is true of all enzymes? Micro Ques 1 ( D ) A They are denatured at temperatures above 60 oC. B They are inhibited at low pH values. C They catalyse the breakdown of large molecules into smaller ones. D They are required in small amounts.
  36. 36. 2 ml of amylase solution is added to 5ml of starch solution which is kept in a water bath maintained at 70 oC. Then the mixture is cooled down from 70 oC to 10oC. Which of the following shows the change in the reaction rate of this mixture ? Micro Ques 2 ( D )
  37. 37. An enzyme may be inactivated by ___________. Micro Ques 3 ( B ) A removing the products of the reaction as they appear B blocking its active site C halving the concentration of the enzyme D adding another metal as co-enzyme
  38. 38. MicroQuestion • Qn1: Enzymes speed up rate of reaction, Highly specific in their reaction. Remain chemically unchanged at end of reaction, hence they are required in small amount. The enzymes reaction can be affected by temperature and pH. • Qn2: It refers to the depression in the enzyme that substrate can fit it. • Qn3: Breakdown of complex molecules and build up of complex molecules from simples molecules.
  39. 39. !! Activity Time !! Each of you should get either a KEY or a LOCK
  40. 40. You have 5 mins to look for the key that opens your lock!
  41. 41. Lets Reflect! • What does the lock represent? • Enzyme • What does the key represent? • Substrate • Where is the active site? • In the lock
  42. 42. Issues with the Lock & Key Hypothesis The lock (enzyme) changes shape after the reaction *Enzymes are unchanged after the reaction The key (substrate) does not give rise to any new products *Substrates give rise to new products with the help of enzymes
  43. 43. Enzymes In conclusion, enzyme action is specific due to the shape of the substrate and active site being complementary to each other.

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