1. E N Z Y M E S What are they? What do they do? How do they work?
What can affect how an enzyme works?
Enzyme class

2. What are enzymes? Enzymes are __________
(tertiary and quaternary structures)
proteins

3. DEFINITION An enzyme is a biological catalyst.
This means it is a protein (biological molecule) that speeds up chemical reactions (a catalyst).
A substrate is the molecule on which an enzyme acts.

4. Enzymes… Have names that usually end in -_____. -Sucrase -Lactase
-Maltase
- ase

5. ENZYME CLASS/NOMENCLATURE
Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases
Example: [EC ] an oxidoreductase

6. ENZYME CLASS/NOMENCLATURE
All enzymes will have their unique EC number.
The first three numbers are the class, sub-class and sub-subclass.
The last is the serial number for the enzyme in its subclass.
BCH3101

7. ENZYME CLASS

8. BCH3101

9. BCH3101

16. WHAT ENZYMES DO
Enzymes act in chemical reactions that build up (join simple molecules to make a bigger, complex compound) or break down (digest) big complex molecules to small simple substances.
Examples:
Amino acids are joined to make proteins (building up or anabolic reactions)
Starch is broken down to glucose (breaking down or catabolic reactions)

18. SOME TERMS TO REMEMBER
SUBSTRATE: the molecule upon which an enzyme acts.
Example: The enzyme amylase breaks down starch. So starch is the substrate for amylase.
ACTIVE SITE (of the enzyme) part of the enzyme that binds to the substrate during a chemical reaction.
PRODUCT: the molecule obtained as a result of the enzyme’s action.
RATE OF REACTION: how an enzymes works. It is measured by recording either the disappearance of substrate or the appearance of product. In other words, it records the changes in concentration of either the substrate or the product as the reaction proceeds.

19. PROPERTIES OF ENZYMES
Enzymes are specific. They will react only with a one given type of substrate.
Example: an enzyme that breaks down proteins will not break down fats
Enzymes are affected by extreme temperatures and pH. Each enzyme has an optimum pH and temperature at which it works best.

20. PROPERTIES OF ENZYMES
Enzymes are not affected by the chemical reaction they help take place.
- same enzyme can be reused again
- a small number of enzymes can carry out a great number of chemical reactions to produce a lot of products
Enzymes are affected by poisons, such as toxins and heavy metals, and by high concentrations of salts

21. HOW ENZYMES WORK
A) lock and key model: the substrate has a similar shape to the one in the active site – an enzyme-substrate complex forms – a product is obtained and the unchanged enzyme is free to start again.

22. Enzymes… are ________ for what they will catalyze.
fit with substrate like a ____ and ____.
specific
lock
key

23. B) induced fit model
The substrate does not have a similar shape to the active site in the enzyme; instead, when the enzyme approaches the substrate, the enzyme’s shape changes so that the substrate can now “fit” in the active site.

24. Characteristics of Enzymes?
speed up chemical reactions
are required in minute amounts
are highly specific in their action
are affected by temperature
are affected by pH
Some catalyse reversible reactions
Some require co-enzymes
Are inhibited by inhibitors

25. Enzymes…
…are _______. They are not consumed (used up) in the reactions they catalyze.
reusable

26. (1) Enzymes Speed up chemical reactions
Activation Energy with enzyme
Activation Energy without enzyme
Substrate
Products:
Energy
Time
By lowering the activation energy needed to start the reaction.

27. Enzymes catalyze reactions by weakening chemical bonds, which ________ activation energy.
lowering

28. (2) Enzymes are required in minute amounts
Chemically unchanged
Sucrase
Sucrose Glucose + Fructose
They remain chemically unchanged after catalysing the reactions.
The same enzyme molecules can be reused over again.
Therefore, only a small amount of enzyme is required to catalyse a large number of reactions

29. (3) Enzymes are highly specific
Starch Maltose
Amylase
Maltose Glucose + Glucose
Maltase
Each chemical reaction is catalysed by its own specific, unique enzyme.
This is due to every enzyme’s specific 3-d configuration.
How the shape of an enzyme affects its function can be explained by the “LOCK & KEY HYPOTHESIS”.

30. FACTORS AFFECTING ENZYME-CONTROLLED REACTIONS
Temperature pH
Cofactors and coenzymes
(these increase the rate of reaction if present, they are necessary for the enzyme to work; e.g. vitamins)
Concentration of substrate
Concentration of enzymes
Inhibitors

31. Factors That Influence Enzyme Activity
Temperature pH
Cofactors & Coenzymes
Inhibitors

32. HOW TEMPERATURE AFFECTS ENZYMES
At low temperatures, enzymes are inactive or work very slowly.
As the temperature increases, enzymes become more active and the rate of reaction increases until the optimum temperature, when the highest rate of reaction is achieved.
At higher temperatures, the enzymes are denatured (destroyed) so they can no longer bind to the substrate and no reaction takes place.
HOW TEMPERATURE AFFECTS ENZYMES

33. Very high or very low pH affects how enzymes work, as extreme pH will denature the enzyme.
Remember each type of enzyme has its own optimum pH at which it works best.
HOW pH AFFECTS ENZYMES

34. pH and temperature of different enzymes

35. Substrate concentration
The rate of an enzyme-controlled reaction increases as the substrate concentration increases, until the enzyme is working at full capacity
At this point, the enzyme molecules reach their turnover number and assuming that all other conditions such as temperature are ideal, the only way to increase the speed of the reaction even more is to add more enzymes

36. Enzyme concentration
In any reaction catalyzed by an enzyme, the number of enzyme molecules present is very much smaller than the number of substrate molecules.
When an abundant supply of substrate is available, the rate of reaction is limited by the number of enzyme molecules present.
In this situation, increasing the enzyme concentration increases the rate of reaction.

37. Inhibitors

38. Co-factor and co-enzyme Michaelis-Menten and Lineweaver-Burke Plot

39. Apoenzyme
An enzyme that requires a cofactor but does not have one bound
An apoenzyme is an inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor

40. Holoenzyme An apoenzyme together with its cofactor
A holoenzyme is complete and catalytically active

41. cofactor
non-protein chemical compound that is bound to a protein and is required for the protein's biological activity.

42. Cofactor Examples of some enzymes that require metal ions
as cofactors is shown in the table below
 cofactor
 enzyme or protein
 Zn++
 carbonic anhydrase
 alcohol dehydrogenase
 Fe+++ or Fe++
 cytochromes, hemoglobin
 ferredoxin
 Cu++ or Cu+
 cytochrome oxidase
 K+ and Mg++
 pyruvate phosphokinase

43. Coenzymes
coenzymes are organic molecules that are required by certain enzymes to carry out catalysis
They bind to the active site of the enzyme and participate in catalysis but are not considered substrates of the reaction.

44. coenzymes in group transfer reactions
 abbreviation
 entity transfered
 nicotine adenine dinucelotide
 NAD - partly composed of niacin
 electron (hydrogen atom)
 nicotine adenine dinucelotide phosphate
 NADP -Partly composed of niacin
 flavine adenine dinucelotide
 FAD - Partly composed of riboflavin (vit. B2)
 coenzyme A
 CoA
 Acyl groups 
 coenzymeQ
 CoQ
 electrons (hydrogen atom)
 thiamine pyrophosphate
 thiamine (vit. B1)
 aldehydes
 pyridoxal phosphate
 pyridoxine (vit B6)
 amino groups
 biotin
 carbon dioxide
 carbamide coenzymes
 vit. B12
 alkyl groups

46. Michaelis-Menten

47. Enzyme Kinetics Equation

48. The Michaelis-Menten Equation
Enzyme catalyzed reactions can be described mathematically
At high concentration of substrate, the E is saturated with S and the reaction rate is independent of the substrate concentration (zero order with respect to S). The maximum velocity is vmax
At low concentrations of substrate - the reaction is first order with respect to S and first order with respect to E)

49. BCH3101

50. Michaelis-Menten: Equation

51. Lineweaver–Burk plot
The y-intercept of such a graph is equivalent to the inverse of Vmax
The x-intercept of the graph represents −1/Km
Quick, visual impression of the different forms of enzyme inhibition
Lineweaver, H and Burk, D. (1934). "The Determination of Enzyme Dissociation Constants". Journal of the American Chemical Society 56 (3): 658–666.

52. Michaelis-Menten vs Lineweaver–Burk plot
Where:-
 V is the reaction velocity (reaction rate)
Km is the Michaelis–Menten constant
Vmax is the maximum reaction velocity
[S] is the substrate concentration

53. Inhibitors

57. Michaelis-Menten : Inhibitors

58. Lineweaver–Burk : Inhibitors

59. Lineweaver–Burk : Inhibitors

60. Non-competitive Inhibitors
uncompetitive Inhibitors

62. Enzyme Activity
Specific Activity is the number of units of activity per amount of total protein.
Ex. A crude cell lysate might have a specific activity of 0.2 units/mg or ml protein upon which purification may increase to 10 units/mg or ml protein.
One unit would be the rate formation of one μmol product per minute at a specific pH and temperature with a substrate concentration much greater than the value of Km.