1. SBI4U BIOCHEMISTRY
Enzymes
Ms. Manning

2. Essential Questions:
What are enzymes and what is their role in normal cellular function?
What are the chemical structures and mechanisms of various common enzymes?
What are the factors that affect the function of enzymes in cellular processes?
Why/how are enzymes used in the food and pharmaceutical industry?

3. What does this look like?
Map of Glucose Metabolism

4. Homework Question:
What is a metabolic (biochemical) pathway? What is the role of enzymes in metabolic pathways?

5. How are macromolecules brought into the body converted into molecules that make up the body?
The body’s metabolism consists of a large number of biochemical pathways that consist of sequences of chemical reactions.
convert substrate molecules into specific products needed by the body.

6. Types of Biochemical Pathways
There are two fundamental types of biochemical pathways.
Anabolic pathways build complex products from less complex substrates
Catabolic pathways break down complex molecules to make energy available for biological processes.

7. Which of these reactions are: a) anabolic b) catabolic?
Neutralization (acid-base) reaction
Hydrolysis reaction
Oxidation-reduction (redox) reaction
Condensation (dehydration) synthesis reaction

8. Enzymes Proteins (globular structure) that catalyze chemical reactions
In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzymes converts them into different molecules, called the products
Why is an enzyme called a catalyst?

9. Elephant Toothpaste Recipe
- Hydrogen Peroxide
- Soap
2 H2O2  O2 + 2 H2O
What will happen to the new recipe when a catalyst is added?

10. Enzyme Characteristics
What characteristic was presented in the demo?
Speed up chemical reactions!
Almost all cellular reactions need enzymes to occur at significant rates.
Without enzymes, chemical reactions would still occur, but they would happen much to slowly to sustain life.

11. How do enzymes work?

12. Enzymes in Digestion

13. Enzyme Characteristics
What characteristic was presented
in the lock and key activity?
Enzymes are specific for one particular reaction or group of related reactions.
Lactose
(milk sugar)
Triglycerides
(lipid)
Amylose
(starch)
Protein
Lactase
Lipase
Amylase
Protease

14. Homework Question: #3-4, pg. 115
What is the
difference?

15. Homework Question: #1 pg. 115
Enzymes called catalysts because they speed up chemical rxns
Interact with substrates to convert them to products
Substrates drawn to active site through weak bonds
Intra-substrate bonds weakened and substrate is split apart
Weakening of intra-substrate bonds by enzyme makes rxn occur faster

16. Enzyme Action and the Hydrolysis of Sucrose
Enzyme sucrase breaks down a molecule of sucrose into glucose and
fructose

17. Homework Question: #2, pg. 115
Catabolic – enzyme breaks substrate apart – exergonic reaction (yeilds energy)
Anabolic – enzyme builds larger substrate by joining two substrates – endergonic reaction (requires energy)

18. Enzyme Structure Hormone-sensitive lipase HSL catalyzes the
breakdown of stored fat

19. The active site of HSL (green) catalyzes the breakdown of TGs
Adipocyte
(fat cell) TG
The active site of HSL (green)
catalyzes the breakdown of TGs
in a process called Lipolysis.
Glycerol FA
Triglyceride
HSL
+ H2O (hydrolysis) FA
Glycerol FA
Diglyceride
Composite image of the HSL model to illustrate the putative localization of the regulatory module of in the three-dimensional structure. The HSL model is displayed in spacefill representation, with the residues in the catalytic triad colored green (Ser), white (Asp), and magenta (His).
Contreras J A et al. J. Biol. Chem. 1996;271:
©1996 by American Society for Biochemistry and Molecular Biology

20. Activation Energy and Enzymes

21. What is activation energy?
a) The thermal energy associated with random movements of molecules
b) The energy released through the active breaking of chemical bonds
c) The difference in free energy between reactants and products
d) The energy required to initiate a chemical reaction

22. Explain the role of activation energy in a reaction
Explain the role of activation energy in a reaction. How does an enzyme affect activation energy?
Activation energy  the amount of energy needed to trigger the reaction.
Without reaching the activation energy, reactions can't take place.
Enzymes catalyze this process by lowering the amount of energy required to activate the reaction.

23. Activation Energy and Enzymes
The amount of activation energy that is required is considerably less when enzyme is present.

24. Factors that Affect Enzyme Activity (reaction rate)
Q#1-4 pg. 116 on enzyme worksheet

26. Enzyme is said to be denatured
– no longer a catalyst

30. Enzyme is said to be denatured
– no longer a catalyst

34. Other Regulators of Enzyme Activity

35. Enzyme Cofactors (pg. 117)
Q#1 - Describe the general role of cofactors in enzyme activity
Non-protein, bound to enzyme
May be organic or inorganic ions
Enhance enzyme activity - “helper”
change enzyme active site shape
make active site more reactive

36. Examples of Inorganic Cofactors
Mg in Chlorophyll
Fe in heme group of hemoglobin

37. Organic Cofactors Active site Coenzymes e.g., NAD Prosthetic group
(perm. attached)
Active site
Enzyme
Coenzyme
(detaches)
Prosthetic Groups
e.g., FAD

38. Important Organic Cofactors
Nicotinamide Adenine Dinucleotide (NAD)
coenzyme derived from vitamin B3
carries and transfers electrons and functions as oxidizing agent in redox reactions
Active site
Enzyme
Coenzyme
(detaches)
e.g., NAD

39. Important Organic Cofactors
Flavin Adenine Dinucleotide (FAD)
prosthetic group
like NAD, FAD functions as a reducing agent in cellular respiration and donates electrons to the electron transport chain
Active site
Enzyme
Prosthetic group
(perm. attached)
Prosthetic Group
e.g., FAD

40. Covalent Modulation
Enzymes can be activated or inactivated by covalent modification.
A common example is phosphorylation of an enzyme (addition of a phosphate group to the amino acids serine, threonine, or tyrosine) mediated by another enzyme called a kinase .
The phosphorylation is reversible, and other enzymes called phosphatases typically catalyze the removal of the phosphate group from the enzyme.

41. Enzyme Inhibitors Types of Inhibitors Enzymes may become deactivated
Temporarily or Permanently
Types of Inhibitors
Reversible Inhibitors
Irreversible Inhibitors

42. Reversible Inhibitors
Used to control enzyme activity
Involves the substrate or the end product of the reaction
For example: a build up of the end product – called feedback inhibition

43. Competitive Inhibitors
Competitive Inhibitors have a similar shape as the substrate
Compete with the substrate to bind to the active site, but no reaction occurs
Block the active site so no substrate can fit

44. Competitive Inhibition

45. Non-Competitive Inhibitors
Binds to a different site on the enzyme
Does not compete with the substrate to bind to the active site
Two ways to non-competitively inhibit the enzyme:
1. slow down the reaction or
2. changes the shape of the active site (allosteric inhibition)
Which of the following diagrams represents allosteric inhibition?

46. Substrate active site enzyme Inhibitor site enzyme active site
(a) Reaction
Substrate
active
site
enzyme
Inhibitor
site
Substrate binds with the active site of enzyme
Reaction occurs and product molecules are produced
(b) Inhibition
enzyme
active
site
Inhibitor
site
Inhibitor
Inhibitor binds with the inhibitor site of the enzyme
Substrate may still bind with the enzyme but the reaction rate is reduced

47. Substrate active site enzyme Substrate active site Inhibitor
(a) Reaction
Substrate
active
site
enzyme
Substrate binds with the active site of enzyme
Reaction occurs and product molecules are produced
(b) Inhibition
Substrate
active
site
enzyme
Inhibitor
Inhibitor binds with the inhibitor site of the enzyme and changes the structure of the active site
Inhibitor prevents binding of the substrate by changing the active site shape

48. Substrate active site enzyme Substrate active site Inhibitor
(a) Reaction
Substrate
active
site
enzyme
Substrate binds with the active site of enzyme
Reaction occurs and product molecules are produced
(b) Inhibition
Substrate
active
site
enzyme
Inhibitor
Inhibitor binds with the inhibitor site of the enzyme and changes the structure of the active site
Inhibitor prevents binding of the substrate by changing the active site shape

49. Substrate active site enzyme Inhibitor site enzyme active site
(a) Reaction
Substrate
active
site
enzyme
Inhibitor
site
Substrate binds with the active site of enzyme
Reaction occurs and product molecules are produced
(b) Inhibition
enzyme
active
site
Inhibitor
site
Inhibitor
Inhibitor binds with the inhibitor site of the enzyme
Substrate may still bind with the enzyme but the reaction rate is reduced

50. Check for Understanding
Q#2 – Distinguish between competitive and non-competitive inhibition
Competitive
inhibitor competes with the substrate for binding to the active site of the enzyme and prevents reaction
Non-competitive
inhibitor does not compete for the active site,
binds to a different site,
either slows down or completely prevents reaction.

51. Check for Understanding
Q#2 – Explain how allosteric inhibitors differ from other non-competitive inhibitors:
 While non-competitive inhibitors reduce enzyme activity and slow down the reaction rate, allosteric inhibitors block the active site altogether and prevent its functioning completely

52. Irreversible Inhibitors
Also called poisons
For example: certain heavy metals
E.g., cadmium, lead, mercury
Retained in the body and lost slowly
Cyanide is a poison that prevents the activity of cytochrome C oxidase, an enzyme in the electron transport chain in the cell. It therefore inhibits ATP production and cellular respiration.

53. Cytochrome c oxidase

54. Why are enzymes so tightly regulated by co-factors and inhibitors?

55. Control of Metabolism
Biochemical reactions are controlled in part by the specificity of substrate biding, but the human body could not function if all enzymes were present together and all operating maximally with no regulation.
There would be biochemical chaos with substances being synthesized and degraded at the same time.
Instead, the body tightly regulates enzymes through metabolic pathways and by controlling specific enzymes within a pathway.
This approach allows an entire pathway to be turned on or off by simply regulating one or a few enzymes.
Metabolic pathways can also be regulated by switching specific genes on or off.

56. Why is it important to know how enzymes are regulated?
Enzymes play a critical role in everyday life. Many heritable genetic disorders occur because there is a deficiency or total absence of one or more enzymes.
Other disease conditions (e.g., cancer) result because there is an excessive activity of one or more enzymes.
Routine medical tests monitor the activity of enzymes in the blood, and many of the prescription drugs (e.g., penicillin,) exert their effects through interactions with enzymes.
Enzymes and their inhibitors can be important tools in medicine, agriculture, and food science.

57. Test study tip:
Create a concept map that summarizes the regulation of enzyme activity
Include the following terms:
temperature
Active site
Co-factors pH
Enzyme inhibitors
Co-enzymes
Enzyme concentration
Competitive inhibitor
Allosteric inhibitor
Substrate concentration
Non-competitive inhibitor
Irreversible inhibitors
denature
Inhibitor site
Enzyme reation rates
Reversible inhibitors