Energy and Enzymes
Ch. 6
1
6.1 Cells and the Flow of
Energy
• Energy – The ability to do work or bring about a change
Kinetic energy
• Energy of motion
• Mechanical
Potential energy
• Stored energy
• Chemical energy
2
Flow of Energy
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solar energy heat
heat
heat
heat
Chemical
energy
Mechanical energy
3
Two Laws of
Thermodynamics
• First law:
Law of conservation of energy
Energy cannot be created or destroyed, but can be changed from one form to another
• Second law:
Law of entropy
When energy is changed from one form to another, there is a loss of usable energy
Waste energy goes to increase disorder
4
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heat
CO2
sun
H2O carbohydrate solar energy
producer
Carbohydrate Metabolism
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heat
carbohydrate
uncontracted muscle
contracted muscle
6
Cells and Entropy
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H2O
C6H12O6
CO2
Glucose
Carbon dioxide and water
• more organized
kinetic
• more potential energy
• less organized
• less potential energy
energy
• less stable (entropy)
• more stable (entropy)
a.
+
H
+
H
channel protein
+
H
+
H
+
H
+
H
+
H
+
H
+
H
Unequal distribution of hydrogen ions
• more organized
b.
+
H
+
H
+
H
+
H
+
H
+
H
+
H
+
H
+
H
Equal distribution of hydrogen ions
• less organized
• more potential energy
• less potential energy
• less stable (entropy)
• more stable (entropy)
7
6.2 Metabolic Reactions and Energy
Transformations
• Metabolism
Sum of cellular chemical reactions in cell
Reactants participate in a reaction
Products form as result of a reaction
• Free energy is the amount of energy available to perform work
Exergonic Reactions - Products have less free energy than reactants (release energy)
Endergonic Reactions - Products have more free energy than reactants (require energy input)
8
• Exergonic
CH4 + 2O2 CO2 + 2H2O
• Endergonic
Solar en + 6CO2 + 6H2O C6H12O6 + 6O2
9
ATP: Energy for Cells
• Adenosine triphosphate (ATP)
High energy compound used to drive metabolic reactions Constantly being generated from adenosine diphosphate (ADP)
• Composed of:
Adenine, ribose (together = adenosine), and three phosphate groups
• Coupled reactions
Energy released by an exergonic reaction captured in ATP
ATP is used to drive an endergonic reaction
10
The ATP Cycle
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adenosine triphosphate
ATP is unstable and has a high potential energy.
P
P
P
ATP
11
The ATP Cycle
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adenosine triphosphate
ATP is unstable and has a high potential energy.
P
P
P
Endergonic Reaction:
• Creation of ATP from
ADP and Prequires input of energy from
Other sources.
ATP
• Has positive delta G.
• Example: cellular respiration ADP
+
P
Exergonic Reaction:
• The hydrolysis of ATP releases
Previously stored energy, allowing the change in free energy to do work and drive other processes.
• Has negative delta G.
• Examples: protein synthesis, nerve conduction, muscle contraction
P
adenosine diphosphate
+
P
+
phosphate
ADP is more stable and has lower potential energy than ATP.
P
12
Coupled Reactions
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1
2
Myosin assumes its
3
ATP splits into ADP
Release of ADP and
resting shape when
and p , causing
p cause myosin to
It combines with ATP.
myosin to change its
again change shape
shape and allowing it
and pull against actin,
to attach to actin.
generating force and motion. actin
P myosin ATP
ADP