1. Chapter 6
Metabolism

2. Two Laws of Thermodynamics
Biology, 9th ed,Sylvia Mader
Chapter 06
Two Laws of Thermodynamics
Metabolism
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

3. 6.2 Metabolic Reactions and Energy Transformations
Biology, 9th ed,Sylvia Mader
Chapter 06
6.2 Metabolic Reactions and Energy Transformations
Metabolism
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)

4. Biology, 9th ed,Sylvia Mader
Chapter 06
ATP: Energy for Cells
Metabolism
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

5. The ATP Cycle 5 Metabolism Biology, 9th ed,Sylvia Mader Chapter 06
Slide #5
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
adenosine triphosphate
ATP is unstable and has
a high potential energy. P P P
Exergonic Reaction:
• Creation of ATP from
ADP and Prequires
input of energy from
Other sources.
ATP
• Has positive delta G.
• Example: cellular
respiration
ADP + P
Endergonic 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 P + P 5
adenosine diphosphate +
phosphate
ADP is more stable and has lower potential energy than ATP.

6. 6.3 Metabolic Pathways and Enzymes
Biology, 9th ed,Sylvia Mader
Chapter 06
6.3 Metabolic Pathways and Enzymes
Metabolism
Reactions usually occur in a sequence
Products of an earlier reaction become reactants of a later reaction
Such linked reactions form a metabolic pathway
Begins with a particular reactant, proceeds through several intermediates, and terminates with a particular end product
AB C D E FG
“A” is Initial Reactant
B, C, D, E, and F
are Intermediates
“G” is End Product

7. 6.3 Metabolic Pathways and Enzymes
Biology, 9th ed,Sylvia Mader
Chapter 06
6.3 Metabolic Pathways and Enzymes
Metabolism
Enzyme
Protein molecules that function as catalysts
The reactants of an enzymatically catalyzed reaction are called substrates
Each enzyme accelerates a specific reaction
Each reaction in a metabolic pathway requires a unique and specific enzyme
The end product will not be formed unless ALL enzymes in the pathway are present and functional
E1 E2 E3 E4 E5 E6
A  B  C  D  E  F  G

8. Biology, 9th ed,Sylvia Mader
Chapter 06
Energy of Activation
Metabolism
Molecules frequently do not react with one another unless they are activated in some way
Energy must be added to at least one reactant to initiate the reaction
Energy of activation
Enzyme Operation:
Enzymes operate by lowering the energy of activation
Accomplished by bringing substrates into contact with one another

9. Biology, 9th ed,Sylvia Mader
Chapter 06
Energy of Activation
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
energy of
activation
(Ea)
energy of
reactant
energy of
activation
(Ea)
Free Energy
energy of
product
enzyme not present
enzyme present
Progress of the Reaction

10. Enzyme-Substrate Complex
Biology, 9th ed,Sylvia Mader
Chapter 06
Enzyme-Substrate Complex
Metabolism
The active site complexes with the substrates
Causes the active site to change shape
Shape change forces substrates together, initiating bond
Induced fit model
Enzyme is induced to undergo a slight alteration to achieve optimum fit for the substrates

11. Enzyme-Substrate Complex
Biology, 9th ed,Sylvia Mader
Chapter 06
Enzyme-Substrate Complex
Metabolism
Degradation:
Enzyme complexes with a single substrate molecule
Substrate is broken apart into two product molecules
Synthesis:
Enzyme complexes with two substrate molecules
Substrates are joined together and released as a single product molecule

12. Biology, 9th ed,Sylvia Mader
Enzymatic Actions
Chapter 06
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
products
enzyme
substrate
enzyme-substrate
complex
active site
Degradation
The substrate is broken down
to smaller products. a.
enzyme
product
enzyme
substrates
enzyme-substrate
complex
active site
Synthesis
The substrates are combined
to produce a larger product. b.
enzyme

13. Factors Affecting Enzymatic Speed
Biology, 9th ed,Sylvia Mader
Chapter 06
Factors Affecting Enzymatic Speed
Metabolism
Substrate concentration
Enzyme activity increases with substrate concentration due to more frequent collisions between substrate molecules and the enzyme
Temperature
Enzyme activity increases with temperature
Warmer temperatures cause more effective collisions between enzyme and substrate
However, hot temperatures can denature and destroy enzymes pH
Most enzymes are optimized for a particular pH

14. The Effect of Temperature on Rate of Reaction
Biology, 9th ed,Sylvia Mader
Chapter 06
The Effect of Temperature on Rate of Reaction
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(product per unit of time)
Rate of Reaction
Temperature C
Rate of reaction as a function of
temperature
b. Body temperature of ectothermic animals
often limits rates of reactions.
c. Body temperature of endothermic animals
promotes rates of reactions.
b: © James Watt/Visuals Unlimited; c: © Creatas/PunchStock

15. The Effect of pH on Rate of Reaction
Biology, 9th ed,Sylvia Mader
Chapter 06
The Effect of pH on Rate of Reaction
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pepsin
trypsin
(product per unit of time)
Rate of Reaction 1 2 3 4 5 6 7 8 9 10 1 1 12 pH

16. Factors Affecting Enzymatic Speed
Biology, 9th ed,Sylvia Mader
Chapter 06
Factors Affecting Enzymatic Speed
Metabolism
Cells can regulate the presence/absence of an enzyme
Cells can regulate the concentration of an enzyme
Cells can activate or deactivate some enzymes
Enzyme Cofactors
Molecules required to activate enzyme
Coenzymes are nonprotein organic molecules
Vitamins are small organic compounds required in the diet for the synthesis of coenzymes

17. Cofactors at Active Site
Biology, 9th ed,Sylvia Mader
Chapter 06
Slide #17
Cofactors at Active Site
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cofactor
active
site
substrate a. b. 17

18. Biology, 9th ed,Sylvia Mader
Chapter 06
Enzyme Inhibition
Metabolism
Reversible enzyme inhibition
A substance known as an inhibitor binds to an enzyme and decreases its activity
Competitive inhibition – the substrate and the inhibitor are both able to bind to active site
Noncompetitive inhibition – the inhibitor does not bind at the active site, but at an allosteric site

19. Noncompetitive Inhibition of an Enzyme
Biology, 9th ed,Sylvia Mader
Noncompetitive Inhibition of an Enzyme
Chapter 06
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A E
allosteric site 1
enzymes
substrates E 1 E 2 E 3 E 4 E 5 F A B C D E
(end
product) 1
Metabolic pathway produces F, the end product. F
active site E
(end
product) 1 2
F binds to allosteric site and the active site of E1 changes shape. F A E
(end
product) 1 3
A cannot bind to E1; the enzyme has been inhibited by F.

20. Enzyme Inhibitors Can Spell Death
Biology, 9th ed,Sylvia Mader
Chapter 06
Enzyme Inhibitors Can Spell Death
Metabolism
Materials that irreversibly inhibit an enzyme are known as poisons
Cyanide inhibits enzymes required for ATP production
Sarin inhibits an enzyme located at the neuromuscular junction.
Warfarin inhibits an enzyme responsible for the blood clotting process

21. 6.4 Organelles and the Flow of Energy
Biology, 9th ed,Sylvia Mader
Chapter 06
6.4 Organelles and the Flow of Energy
Metabolism
Oxidation-reduction (redox) reactions
Electrons pass from one molecule to another
Oxidation - loss of an electron
Reduction – gain of an electron
Both take place at same time
One molecule accepts the electron given up by the other

22. Photosynthesis and Cellular Respiration
Biology, 9th ed,Sylvia Mader
Chapter 06
Photosynthesis and Cellular Respiration
Metabolism

23. Electron Transport Chain
Biology, 9th ed,Sylvia Mader
Chapter 06
Electron Transport Chain
Metabolism
Consists of membrane-bound carrier proteins found in mitochondria and chloroplasts
Physically arranged in an ordered series
Starts with high-energy electrons
Pass electrons from one carrier to another
Electron energy used to pump hydrogen ions (H+) to one side of membrane
Establishes an electrochemical gradient across the membrane
The electrochemical gradient is used to make ATP from ADP – Chemiosmosis
Ends with low-energy electrons and high-energy ATP

24. ElectronTransport Chain
Biology, 9th ed,Sylvia Mader
ElectronTransport Chain
Chapter 06
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. e–
high-energy
electrons
High-energy electrons
are unstable and have
high potential energy.
This energy is released
in stages, as kinetic
energy, during the
electron transport chain.
energy for
Synthesis of
ATP
electron
transport chain
As energy is released,
the electrons become
more stable and have
less potential energy.
low-energy
electrons e-

25. Chemiosmosis 25 High H+ concentration H+ H+ H+ pump in electron
Biology, 9th ed,Sylvia Mader
Chemiosmosis
Chapter 06
Slide #25
Metabolism
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
High H+ concentration H+ H+
H+ pump in electron
transport chain H+ H+ H+
ATP
ADP + P
ATP
synthase
complex
ADP + P
NADH
NAD + H+
ATP H+
Low H+ concentration 25