BIOLOGY FORM 4 CHAPTER 4 - CHEMICAL COMPOSITION OF THE CELL PART2

1. BIOLOGY FORM 4
CHAPTER 4 PART 2
CHEMICAL COMPOSITION OF THE
CELL
ENZYMES

3. The compound on which an enzyme acts
is the substrate.

4. 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.

5. Explain why life cannot exist
without enzymes.
Reactions would be too slow to
sustain life

8. Synthesized by
ribosomes &
modified by the
Golgi Apparatus

10. DNA –
contains codes
to make protein
mRNA is
synthesised
according to the
instruction of DNA
mRNA leaves
the nucleus and
moves to
ribosome
Ribosomes acts
as a workbench
for mRNA
PRODUCTION OF
INTRACELLULAR ENZYMES
Specific protein is
synthesised using
this information
Protein is
release into the
cytoplasm

12. The production of extracellular
enzymes
DNA carries
the
information
for the
synthesis of
enzymes
Proteins that are
synthesised at the
ribosomes are
transported through
the space within the
rough ER
Proteins are
wrapped in vesicles
that are bud off from
the membranes of
the rough ER
Vesicles fuse with the
membrane of the golgi
apparatus which empty
their contents into the
membranous space

13. Proteins are
modified during
their transport in
the golgi
apparatus
Secretory vesicle
containing proteins
bud off from the golgi
apparatus and travel
to the plasma
membrane
Vesicle then fuse with
the plasma membrane
before releasing the
proteins outside the cell
as enzymes

14. Labelling Exercise

17. 1 Substrate enters active site 2 An enzyme-substrate complex forms
Products form and leave active site
Reaction occurs
4 3

19. BOND FORMATION

20. BOND BREAKING

21. REVERSIBLE REACTION

22. ACTIVE SITE OF AN ENZYME
• Enzymes have a specific site called an active site.
• The active site has a specific shape & charges to
which only a specific substrate will fit.

23. Active site:
very small
(3-12 amino acids)
Active
Sites
• It only allows substrates with a
COMPLEMENTARY shape and charge to bind with
it to form an Enzyme-Substrate Complex

26. 4. Not destroyed by the reactions they catalyse.
5. Needed in small quantities.

27. Enzymes are highly specific
Amylase
Starch Maltose
Maltose Maltase
Glucose + Glucose
• 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”.

28. 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. 6 Factors affecting enzyme activity
1) Temperature
2) pH
3) Substrate Concentration
4) Enzyme Concentration
5) Cofactors
6) Inhibitors

30. 1.
Factors which affect enzyme action:

33. Enzyme activity is affected by temperature
• Enzymes can function
over a range of
temperatures.
• But all enzymes have
their own optimum
temperature.

35. Optimum temperature
• The optimum temperature is the temperature at which
the enzyme is most active, catalysing the largest
number of reactions per second.
• Different enzymes have different optimum temperature
• Example:
most enzymes in the human body
functions best at about 37- 40oC, near body
temperature.
Enzymes of thermophilic bacteria that live
in hotsprings will have very high optimum
temperatures.

38. How enzyme activity is affected by temperature
Increasing temp up to optimum temp.
• At low temperature, enzymes are INACTIVE.
• As temperature rises, the rate of enzyme activity
increases (usually 2x as active for every 10oC
rise).
• Enzyme reaching maximum rate of activity at OT
NOTE:
Describe the
enzyme activity with
respect to the Rate-
Temperature Graph
• Raising the temperature increases the
kinetic energy supplied to the substrate
and enzyme molecules.
• This increases the no. of collisions
between enzyme and substrate molecules.
• Increasing the rate of formation of enzyme-substrate
complex.
• Rate of formation of the products increases
up till the optimum temperature

39. How enzyme activity is affected by temperature
Increasing temp beyond optimum temp.
• Beyond the optimum temperature, rate of
enzyme activity deceases.
• Until it is completely denatured by the extreme
heat
NOTE:
Describe the
enzyme activity with
respect to the Rate-
Temperature Graph
• Increase in temperature increases the
vibrations of the atoms in the enzymes.
• Beyond the OT, the vibrations are so
violent that they break the hydrogen bonds
that hold the 3-D structrure in place.
• The enzyme loses its shape and active site
• The enzyme is DENATURED.

40. At Temperatures above the Optimum:
 molecules vibrate and twist so rapidly that
some of their hydrogen bonds and
hydrophobic interactions BREAK
molecule loses the secondary & tertiary
structure

41. Functional
protein
Denatured
protein

42. Over a range of 0-40°C,
the rate of an enzyme
controlled reaction is
doubled for every rise of
10°C
More collisions = More ES
complexes and thus more product

43. Question:
A decrease in temperature decreases
the kinetic energy of molecules in a
solution. Explain how a decrease in
temperature decreases the rate of an
enzyme-controlled reaction. (2)
Less collisions = fewer ES complexes
and thus less product

44. 2.
Factors which affect enzyme action:

45. Most enzymes work at
pH values from 6 to 8.
Narrow pH
optimum
1 2 3 4 5 6 7 8 9

47. What happens to the enzyme
structure if pH changes?
Disruption of ionic bonds:
Tertiary Structure of enzyme changes

48. How enzyme activity is affected by pH
At extreme pH conditions
• Enzymes are DENATURED
• Extreme changes in the pH causes:
 A change in the charges at the active sites which
repels the substrate molecules, preventing them from
binding.
 The irreversible alteration to the bonds that holds the
shape of the enzyme. Enzyme thus loses its original
3-D structure. The active site loses its shape.

49. Factors which affect enzyme action:
3. Substrate Concentration
Vmax

50. Explain the part of the graph
indicated:

51. Explain the part of
the graph indicated:

52. Explain the part of the graph
indicated:

53. Explain the part of
the graph indicated:

55. Point
X

56. • Independent Variable: Substrate concentration
From 0 to Point X
Description Explanation
As the [substrate] increases,
the rate of reaction increases
until Point X when rate of
reaction reaches its maximum.
At any [substrate] before Point
X, there are more enzyme
molecules than substrate
molecules
At Point X, all the enzyme
active sites are occupied by
substrate molecules
• LIMITING FACTOR IS  Substrate concentration

57. • Independent Variable: Substrate concentration
Beyond Point X
Description Explanation
Graph remains constant
/ becomes a plateau
after Point X.
Maximum rate of
reaction
After point X, the rate of reaction does not
increase even when [substrate] increases.
This is because all the enzyme molecule’s
active sites are being occupied at any one
time. That is, all the enzyme molecules
are saturated.
Amount of products formed per unit time
remains constant
• LIMITING FACTOR IS  Enzyme concentration

58. Factors which affect enzyme action:
4. Enzyme Concentration
Rate of
reaction
Enzyme concentration
[unlimited substrate]

59. 2. Enzyme Concentration

60. THE EFFECT OF ENZYME
CONCENTRATION ON ENZYME ACTION
 Assuming that the
amount of substrate is
not limiting, an
increase in enzyme
concentration
causes an increase
in the reaction rate.

61. Substrate Concentration Versus Rate of
0.4moldm-3 Enzyme
0.2moldm-3 Enzyme
Rate of Reaction
(B)
(A)
X Y
Reaction
Substrate Concentration / Arbitrary Units

62. • Independent Variable: Substrate concentration
From 0 to Point Y
Description Explanation
Rate of reaction
increases as [Substrate]
increases for both
Graphs A and B.
At any [Substrate] before Point Y, there
are more enzymes than substrate
molecules.
At Point X, all the enzyme active sites are
occupied by substrate molecules
Rate of reaction of (B) is
double that of (A)
There are double the number of enzyme
molecules in (B). Double the frequency of
collision between Enzyme and Substrate
molecules in (B)
LIMITING FACTOR  Substrate Concentration

63. • Independent Variable: Enzyme concentration
Beyond Point Y
Description Explanation
Graph remains
constant /
becomes a
plateau after
Point X.
Maximum rate
of reaction
After point X, the rate of reaction does not increase
even when [substrate] increases.
This is because all the enzyme molecule’s active sites
are being occupied at any one time. That is, all the
enzyme molecules are saturated.
Amount of products formed per unit time remains
constant
Rate of reaction
of (B) is double
that of (A)
Double the number of enzyme molecules in (B).
Double the number of E-S complex formed per unit
time. Therefore, double the amount of products formed
LIMITING FACTOR  Enzyme Concentration

64. Factors which affect enzyme action:
5. COFACTORS
 essential to the catalytic activity of some enzymes.
may alter the shape of enzymes slightly to make the active
sites functional or to complete the reactive site.
 Eg. coenzymes (organic molecules) or activating ions (eg.
Na+, K+..)
 Eg Vitamins eg. Vit B1, Vit B6
NAD
(nicotinamide
adenine dinucleotide)

65. Question:
Suggest an explanation for the following
observation:
a)Some vitamins are required for efficient
enzyme action. (2)
To form coenzymes that help enzymes
function.

66. Factors which affect enzyme action:
6. Enzyme activity is slowed/stopped by
inhibitors eg. heavy metals like lead, mercury

67. SUMMARY: ENZYMES
1. Enzymes work very rapidly and help to speed up
biological reactions.
2. Enzymes can be used multiple times (however they
do degrade eventually).
3. Enzymes can work in both directions of a chemical
reaction.
4. Enzymes have optimal temperatures and pH that they
will operate. Beyond these optimum ranges they will
either not work or become denatured
(unfolded/breakdown).
5. Enzymes are usually specific to one particular
substrate.

68. ENZYMES IN DAILY LIFE
State the use of enzyme in:
 Food production
 Dairy industry
 Biological detergent
 Textile industry
 Leather industry
 Paper industry

70. ENZYMES IN CLOTHES/DISHWASHER DETERGENTS
 People use biological detergents to remove stains.
 Biological washing powders contain proteases and
lipases.
 These enzymes break down proteins and fats in the
stain.
Advantages
Enzymes give you a
cleaner wash.
Work at lower
temperatures-this
means you use less
electricity.
Disadvantages
If water too hot,
enzymes become
denatured.

72. ENZYMES IN BABY FOOD
Proteases are used to make baby food.
 Proteases ‘pre-digest’ some of the protein in
the food.
Advantages
Make it easier for a baby’s
digestive system to cope
with.

73. USE OF ENZYMES
Pineapple (Ananas comosus,
right) contains the enzyme
papain which is used in meat
tenderization processes and
also medically as an anti-inflammatory
agent.

74. Meat Tenderizer
Papain
Protease found in papaya
as meat tenderizer

75. STARCH(HFCS)
Carbohydrases are used to convert starch
into sugar (glucose) syrup.
Did You Know?
HFC stands for High
Fructose Corn
Syrup.

76. Rennet -
• Produced from stomach of cows
enzyme rennin obtained either from calf stomach or
microorganism.
• Cut casein proteins in milk into smaller pieces
• solidify milk

77. Protease Usage in Dairy
Products
• Make creamier yogurt products
• Hydrolyze whey proteins -- dairy products less
allergic

78. Lactose intolerance
Lactose intolerance people
No digestion of lactose
Remain in digestive system
Fermented by bacteria
GI symptoms
Tablet of lactase
nausea, cramps, bloating,
gas,& diarrhea -- within 4h

79. Reaction
Substrate: Lactose
Lactose + H2O
-galactosidase
Glucose + Galactose
hydrolysis
Enzymes
Lactase=β- Galactosidase
Application :-
Production of low-lactose dairy product
Lactose-intolerant people
Ice-cream -- creamier, minimize crystallinization & sweeter-tasting

80. Lipases
Source-
Animal --kid, calf, lamb
Plant– mucor meiheri
Milk fat
Lipase
Free fatty acids (flavour production)
hydrolyse
Enhancement of
cheese flavor

81. Fruit juices are extracted using an
enzyme called pectinase.
• Pectin is a substance which helps to stick plant cells
together. Fruits like apple or orange contain a lot of
pectin. The breaking down of pectin makes it much
easier to squeeze juice from the fruit.

82. Cellulase
• Hydrolysis (breaking down) of
cellulose
• Breaks down the surface
cellulose fibers of jeans. Thus
the dye particles are released
from the surface of the jeans,
producing this “faded” affect.
• cellulase helps in the processing of
coffee beans

83. Leather Industry
• Proteases are used in
removing hair from animal
hides.
• Lipases are used in the to
hydrolyze fat particles in the
skin
• Amylases are used to soften
skin.

84. ENZYMES IN SLIMMING AIDS
 The enzyme, isomerase, is used to change glucose
syrup to fructose syrup. Glucose and fructose
contain exactly the same amount of energy.
Fortunately fructose is sweeter than glucose . Much
smaller amounts are needed to make food taste
sweet.
 Fructose is widely used in slimming foods. This is
because the food tastes sweet but contains
fewer calories.

92. To Investigate the Effect of pH on the
activity of Pepsin