1. NOTES: Ch 9 Cellular Respiration: Harvesting Chemical Energy Part 1: The Overview

2. Overview: Life Is Work
● Living cells require energy from outside sources
● Some animals, such as the giant panda, obtain energy by eating plants; others feed on organisms that eat plants

4. ● Energy flows into an ecosystem as sunlight and leaves as heat
● Photosynthesis generates oxygen and organic molecules, which are used in cellular respiration
● Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work

5. Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Organic
molecules
+ O2
Cellular respiration
in mitochondria
ATP
powers most cellular work
Heat
energy

6. 9.1 - Catabolic Pathways & Production of ATP:
● The breakdown of organic molecules is EXERGONIC
● Fermentation is a partial degradation of sugars that occurs without oxygen
● Cellular respiration consumes oxygen and organic molecules and yields ATP

7. Principles of Energy Harvest
● Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:
Chemical Equation:
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
(ATP + heat)

8. Recall: the ATP cycle

9. Redox Reactions: Oxidation and Reduction
● The transfer of electrons during chemical reactions releases energy stored in organic molecules
● This released energy is ultimately used to synthesize ATP

10. ● REDOX REACTIONS: involve electron transfers from 1 substance to another

11. The Principle of Redox ● OXIDATION: loss of electrons
(“energy releasing”)
● REDUCTION: gain of electrons
(“energy storing”)

12. Example of Redox: Na + Cl  Na+ + Cl- Oxidation (loss of electrons)
Reduction
(gain of electrons)

13. ● The electron donor is called the reducing agent
● The electron receptor is called the oxidizing agent

14. Example of Redox: Na + Cl  Na+ + Cl- Na is oxidized;
it is the reducing agent
Na Cl  Na Cl-
Cl is reduced;
it is the oxidizing agent

15. Oxidation of Organic Fuel Molecules During Cellular Respiration:
● During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced:

16. Respiration: C6H12O6 + 6O2  6CO2 + 6H2O
oxidized
C6H12O O2  CO H2O
*the transfer of electrons from 1 element to another, more electronegative element (e.g. from H to O) releases stored potential energy - - this chemical energy can be put to work!
reduced

17. ● Glucose & other fuels are broken down gradually, in a series of steps
● at key steps, H atoms are stripped from glucose and passed to a coenzyme: NAD+
(this is performed by enzymes: dehydrogenase)
NAD H  NADH + H+ H+

18. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
● As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration
● Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP

19. NADH NAD+ 2 e– + 2 H+ 2 e– + H+ H+ Dehydrogenase + 2[H] + H+
(from food) + H+
Nicotinamide
(reduced form)
Nicotinamide
(oxidized form)

20. ● Respiration uses an ELECTRON TRANSPORT CHAIN to break the fall of electrons into several energy-releasing steps (instead of one explosive reaction) e-

21. ● NADH passes the electrons to the electron transport chain
● Oxygen pulls electrons down the chain in an energy-yielding tumble
● The energy yielded is used to regenerate ATP

22. Electron transport chain+
1/2 O2
2 H +
1/2 O2
(from food via NADH)
Controlled
release of
energy for
synthesis of
ATP
2 H+ + 2 e–
ATP
Explosive
release of
heat and light
energy
ATP
Free energy, G
Free energy, G
Electron transport chain
ATP
2 e–
1/2 O2
2 H+
H2O
H2O
Uncontrolled reaction
Cellular respiration

23. ELECTRON TRANSPORT CHAIN:
● consists of molecules, mostly proteins, built into the inner membrane of mitochondria
● NADH carries the electrons to the “top” of the chain

25. ● oxygen captures electrons at the “bottom” of the chain and combines with H+, forming water.
Reduction of
oxygen!

26. SUMMARY OF ENERGY FLOW IN THE CELL:
Food  NADH  E.T.C.  oxygen
(glucose)
**oxygen is the final electron acceptor!

27. The Stages of Cellular Respiration: A Preview
● Cellular respiration has three stages:
1) Glycolysis (breaks down glucose into two molecules of pyruvate)
2) The Citric Acid Cycle, a.k.a. Krebs Cycle (completes the breakdown of glucose)
3) E.T.C. & Oxidative phosphorylation (accounts for most of the ATP synthesis)

28. Glycolysis
Glucose
Pyruvate
Cytosol
Mitochondrion
ATP
Substrate-level
phosphorylation

29. Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Cytosol
Mitochondrion
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation

30. Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Cytosol
Mitochondrion
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation

31. ATP Synthesis:
● The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
● Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration

32. ATP Synthesis:
● A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

33. Enzyme
Enzyme
ADP P
Substrate +
ATP
Product