1. Fundamentals of cellular
energetics
I. Principles of energetics
A. Reaction coupling and ATP
B. Cellular use of energy
C. Redox
II. Oxidation of glucose to CO2
III. ATP synthesis
IV. Photosynthesis

2. Principles of cellular energetics
• Life requires work (organisms perform
work to live, grow, and replicate)
• All organisms use energy for biological
work
• Energy transformations in cells follow the
laws of thermodynamics

3. Reaction coupling review
• An energetically unfavorable reaction
(ΔG˚´>0) can proceed forward if it is
coupled to an energetically favorable
(ΔG˚´<0) reaction
• The hydrolysis of ATP is usually used to
drive reactions forward
ATPADP + Pi
ΔG˚´ = –7.3 kcal/mol (–30.5 kJ/mol)

4. Energy currency of the cell

5. ATP as energy currency
• Cells obtain free energy from either
chemical oxidation or sunlight
• Cells use energy to synthesize ATP
• Cells spend ATP on unfavorable processes
What types of unfavorable processes do
cells spend their hard-earned ATP on?

6. Cellular use of energy
• Biosynthesis (making biomolecules and
biological structures)
• Transport across membranes (against
concentration gradient)
• Movement

7. Redox review (again)
• Oxidation: loss of an electron
• Reduction: gain of an electron
Redox (oxidation-reduction) reactions always
occur in pairs

8. Redox and cellular energetics
• Electrons are transferred and energy is
transduced as chemicals are oxidized
• Energy from oxidation does biological work
• Source of electrons are reduced molecules
like glucose (a sugar) and fatty acids
• Final electron acceptor is O2
• Electron flow produces proton gradient
across a membrane, which is used to
synthesize ATP

9. Electron carriers
NAD+ + 2 e– (+ H+) –> NADH
FAD + 2 e– (+ 2H+) –> FADH2
Cofactors in redox reactions

10. Overview of cellular oxidation
Glycolysis
Citric acid
cycle
Oxidative
phosphorylation
Glucose
CO2
NADH
FADH2
CO2
ADP
NAD+
ATP
NADH
NAD+
FAD
NADH
FADH2
ADP
O2
NAD+
FAD
ATP
H2O

11. Fundamentals of cellular
energetics
I. Principles of energetics
II. Oxidation of glucose to CO2
A. Glycolysis
B. Pyruvate fate
C. Citric acid cycle
III. ATP synthesis
IV. Photosynthesis

12. Glycolysis
• Universal pathway conserved throughout
evolution for producing energy
• Releases chemical energy in glucose
• Forms 2 ATP, 2 NADH, and 2 pyruvate
• Ten enzyme-catalyzed reactions
• Occurs in cytosol

14. Fate of pyruvate
• Oxidation to enter citric acid cycle
Results in complete oxidation of glucose to CO2
Requires O2 as final electron acceptor
• Lactate fermentation (anaerobic)
Muscle during sprint
Yogurt and cheese production by bacteria
• Alcohol fermentation (anaerobic)
Yield ethanol and CO2
Beer, wine, and bread production by yeast

15. Citric acid cycle
• Central pathway in oxidation of fuels
• Eight enzyme-catalyzed reactions
• Product is starting material: cycle
• Each turn yields 2 CO2, 3 NADH, and 1
FADH2 (two turns per glucose)
• Occurs in mitochondria
• (Also called tricarboxylic acid cycle or
Krebs cycle)

17. Energetic accounting
One glucose yields:
• 2 ATP in glycolysis
• 2 NADH in glycolysis
• 2 NADH as pyruvate enters citric acid cycle
• 2 ATP in citric acid cycle
• 6 NADH in citric acid cycle
• 2 FADH2 in citric acid cycle

18. Energetic yield
• Each NADH can produce ~3 ATP and each
FADH2 can produce ~2 ATP when O2 is
present as final electron acceptor
• One glucose completely oxidized to CO2
yields up to ~38 ATP

19. Fundamentals of cellular
energetics
I. Principles of energetics
II. Oxidation of glucose to CO2
III. ATP synthesis
A. Mitochondria
B. Electron transport
C. Oxidative phosphorylation
IV. Photosynthesis

20. Mitochondria
• Power plants of
eukaryotic cells
• Site of citric acid
cycle, electron
transport, and
ATP synthesis

22. Electron transport
• Electrons from NADH and FADH2 are
passed to O2
– Regenerate NAD+ and FAD
– Form H2O
– Release energy
• Electron flow is coupled to pumping of
protons (H+) across inner mitochondrial
membrane (10 H+ per NADH)
• Creates proton gradient across membrane

24. Oxidative phosphorylation
• Proton gradient is used to synthesize ATP
(concentration gradients across a membrane
are a form of energy that can be converted
to chemical energy)
• Catalyzed by ATP synthase (also called
F1F0-ATPase)

25. ATP synthase
• Catalyzes ATP synthesis as protons flow
down their concentration gradient across the
inner mitochondrial membrane
• Two functional components:
– F0 is a transmembrane proton channel
– F1 catalyzes ATP synthesis
• Mechanism involves conformational
changes (H+ translocation powers rotation)