The Working Cell: Energy and Enzymes
CHAPTER 5
•Energy Concepts
• Conservation of Energy
• Entropy and Work
• Chemical Energy and Conversion
•ATP and Cellular Work
• ATP Structure
• Phosphate Transfer and Cycle
•Enzymes
• The
Powering of Chemical Reactions
• Activation Energy
•Loss of Enzyme Function
• Temperature
• Inhibitors
and pH
Energy is defined as the capacity to perform work.
•
Kinetic energy is the energy of motion
•
Potential energy is stored energy
•
Potential energy can be converted into kinetic energy, and vice versa
(but some energy is lost in conversion)
•
Energy can neither be created nor destroyed
Energy Concepts
Energy Lost in Conversion
• Energy lost during conversions is usually heat
energy
– Heat is type of kinetic energy.
• The term entropy as a measure of disorder, or
randomness.
– All energy conversions increase the entropy
(disorder) of the universe.
• Chemical potential energy (food, gasoline,
propane) is used by machines and living things to
do work.
– Not all the chemical energy is converted to work
Energy Conversions: Car and Cell
Food is a Type of Chemical Energy Used By Our Bodies
• Cellular respiration in living things
– The energy-releasing chemical breakdown of
food/fuel molecules.
– Food chemical energy is converted into usable
cellular energy
Food +
Food
Oxygen gas  Carbon dioxide + Water + Usable Cellular Energy
+
(like glucose sugar)
O2

CO2
+ H2O +
ATP
(adenosine triphosphate)
The Working Cell: Energy and Enzymes
CHAPTER 5
•Energy Concepts
• Conservation of Energy
• Entropy and Work
• Chemical Energy and Conversion
•ATP and Cellular Work
• ATP Structure
• Phosphate Transfer and Cycle
•Enzymes
• The
Powering of Chemical Reactions
• Activation Energy
•Loss of Enzyme Function
• Temperature
• Inhibitors
and pH
Usable Cellular Energy (ATP)
• ATP (adenosine triphosphate)
– The basic energy carrier is ADP (adenosine diphosphate)
– Energy is stored in ADP by adding a third phosphate using
a high-energy bond
– The chemical energy from food powers the linkage of
ADP to a third phosphate to become ATP
The Energy Stored in ATP Can Be Used to Perform Work in the Cell
• The energy released by ATP breaking down into
ADP and P can power a variety of needs in the cell
Energized ATP:
ADP
Discharged ATP:
ADP
Powering the synthesis of
molecule Z:
P
P
X
+
Y
Z
The Working Cell: Energy and Enzymes
CHAPTER 5
•Energy Concepts
• Conservation of Energy
• Entropy and Work
• Chemical Energy and Conversion
•ATP and Cellular Work
• ATP Structure
• Phosphate Transfer and Cycle
•Enzymes
• The
Powering of Chemical Reactions
• Activation Energy
•Loss of Enzyme Function
• Temperature
• Inhibitors
and pH
Chemical Reactions within a Cell
• Metabolism is the word that describes all the
chemical reactions within a cell
• Catabolism (catabolic reactions) are breakdown
reactions that liberate energy
• Anabolism (anabolic reactions) are buildup
reactions that absorb energy
Cellular Reactions Either Use or Liberate Energy
• Catabolic/Breakdown Reactions release energy
o Molecules become more disorganized or less structured
X
+
Y
+
Z
• Anabolic/Buildup Reactions absorb energy
o Molecules become more ordered and complex
o ATP needed to power endothermic reactions
A
+
B
+ ATP
C
Cellular Reactions Either Use or Liberate Energy
X + Y
Z
+
Energy Level
• Breakdown Reactions Release Energy
Activation
Z
Energy
X+Y
Time
• Buildup Reactions Absorb or Require Energy
C
+ ATP
C
Energy Level
A + B
Activation
A+ B
Time
Energy
Activation Energy
– Energy needed to allow the
reactants to form products
– Necessary for a chemical
reaction to proceed
Energy Level
• Activation energy
– Activation energy is needed
even for breakdown
reaction to get them going
•
Activation
Z
Energy
X+Y
Time
In the laboratory, we heat the reactants in order to provide
activation energy for a chemical reaction
•
Inside the cell, a different mechanism is required as heating up
the reactants is not possible
Lower the energy required for the reaction
Enzymes Lower Activation Energy and Speed Up Reactions
Figure 5.8
Enzymes Catalyze Chemical Reactions in Living Things
• Biomolecules call enzymes lower activation energy
– Enzymes are folded proteins
– Enzymes act as coordinators in a chemical
reaction, thereby speeding them up
– Enzymes are catalysts for reactions; they speed
them up
Other Aspects of Enzymes
• Each enzyme is very selective
– It has a pocket called the active site where
reactants (substrates) bind for catalysis
– Only substrates with certain shapes can bind to
the enzyme and be catalyzed
– Any particular enzyme therefore catalyzes only a
specific reaction with specific substrates
How Enzyme Catalyzes the Breakdown of Sucrose Sugar
Energy Level
Energy Level
sucrose
glucose
glucose+ +
fructose
fructose
Time
glucose-fructose
How Enzymes Work
Cannot progress because
activation energy too
formidable
The Working Cell: Energy and Enzymes
CHAPTER 5
•Energy Concepts
• Conservation of Energy
• Entropy and Work
• Chemical Energy and Conversion
•ATP and Cellular Work
• ATP Structure
• Phosphate Transfer and Cycle
•Enzymes
• The
Powering of Chemical Reactions
• Activation Energy
•Loss of Enzyme Function
• Temperature
• Inhibitors
and pH
Limitations of Enzyme Catalyzed Reactions
• Three-dimensional structure of an enzyme is key to its
functionality
– Anything which disrupts the intricate 3-D structure of the
active site ruins its ability to catalyze a reaction
– Substrates cannot bind to a distorted active site
• Environmental changes that will ruin enzyme activity
by causing denaturation (unfolding)
– Very high or very low pH
– Very high temperatures (low temps just slow things down)
– The presence of inhibitory molecules
Enzymes Become Non-Functional at pH Extremes and High Temperatures
H
H
OH-
+
+
(products formed per second)
Enzymatic rate
+
H
+
H
H
+
H
+
OH-
+
= denatured, non-functional enzyme
Enzyme within
Enzyme from
Reaction
rate is slow
a body cell
OH
at cold temperatures
hot springs
because
molecules
bacterium
OH
encounter enzyme
less often
OHOH-
H
+
H
OH-
H
+
+
OH-
H
OH-
+
H H
+
+
H
OH-
+
0
= folded, functional enzyme
2
4
6
8 10
pH (in pH units)
(products formed per second)
H
Enzyme within
a body cell
12
Enzymatic rate
Stomach
enzyme
10
20
30 40 50 60
Temperature (oC)
70
Inhibitors That Mimic the Normal Substrate
A competitive
inhibitor
Inhibitors That Bind to Other Enzyme Pockets
A non-competitive inhibitor
The Working Cell: Energy and Enzymes
CHAPTER 5
•Energy Concepts
• Conservation of Energy
• Entropy and Work
• Chemical Energy and Conversion
•ATP and Cellular Work
• ATP Structure
• Phosphate Transfer and Cycle
•Enzymes
• The
Powering of Chemical Reactions
• Activation Energy
•Loss of Enzyme Function
• Temperature
• Inhibitors
and pH