Metabolism:
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