2. Energy in food is stored as carbohydrates (such as glucose), proteins & fats. Before that energy can be used by cells, it must be released and transferred to ATP.

3. Aerobic Cellular Respiration: the process that releases energy by breaking down food (glucose) molecules in the presence of oxygen.
Formula: C6H12O6 + 6O2 → 6CO2 + 6H2O +~ 36 ATP
Fermentation: the partial breakdown of glucose without oxygen. It only releases a small amount of ATP.
Glycolysis: the first step of breaking down glucose—it splits glucose (6C) into 2 pyruvic acid molecules (3C each)

4. The transfer of electrons during chemical reactions releases energy stored in organic compounds such as glucose.
Oxidation-reduction reactions are those that involve the transfer of an electron from one substance to another.

5. In cellular respiration, glucose is broken down in a series of steps.
As it is broken down, electrons from glucose are transferred to NAD+, a coenzyme
When it receives the electrons, it is converted to NADH.
NADH represents stored energy that can be used to make ATP

6. NADH passes the electrons to the electron transport chain, a series of proteins embedded in the inner membrane of the mitochondria.
The electrons (and the energy they carry) are transferred from one protein to the next in a series of steps.

7. Cellular respiration has three stages:
Glycolysis (breaks down glucose into two molecules of pyruvate)
The Citric Acid cycle/Kreb’s Cycle (completes the breakdown of glucose)
Electron Transport Chain and Oxidative phosphorylation (accounts for most of the ATP synthesis)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

8. An Overview of Cellular Respiration–Part 1
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
Cytosol
Figure 9.6 An overview of cellular respiration
ATP
Substrate-level
phosphorylation

9. An Overview of Cellular Respiration—Part 2
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Mitochondrion
Cytosol
Figure 9.6 An overview of cellular respiration
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation

10. An Overview of Cellular Respiration—Part 3
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Mitochondrion
Cytosol
Figure 9.6 An overview of cellular respiration
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation

11. Substrate-level phosphorylation:
Phosphate is added to ADP to make ATP by using an enzyme:
Oxidative phosphorylation:
Phosphate is added to ADP to make ATP by ATP Synthase—a protein embedded in the mitochondria membrane (requires O2)
WAY MORE EFFICIENT!! PRODUCES LOTS MORE ATP!

12. “Glyco”=sugar; “lysis”=to split
In this first series of reactions, glucose (C6) is split into two molecules of pyruvic acid (C3).
This occurs in the cytoplasm of cells and does not require oxygen.
This releases only 2 ATP molecules, not enough for most living organisms.

13. Glycolysis Energy investment phase Glucose 2 ADP + 2 P 2 ATP used
Energy payoff phase
4 ADP + 4 P
4 ATP
formed
2 NAD e– + 4 H+
2 NADH
+ 2 H+
Figure 9.8 The energy input and output of glycolysis
2 Pyruvate + 2 H2O
Net
Glucose
2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used
2 ATP
2 NAD e– + 4 H+
2 NADH + 2 H+

14. The Citric Acid Cycle (also called the Kreb’s Cycle) completes the breakdown of pyruvate and the release of energy from glucose.
It occurs in the matrix of the mitochondria.

15. In the presence of oxygen, pyruvate enters the mitochondria.
Before the pyruvate can enter the Citric Acid Cycle, however, it must be converted to Acetyl Co-A.
Some energy is released and NADH is formed.

16. Converting Pyruvate to Acetyl CoA:
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+ 2 1 3
Acetyl CoA
Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the citric acid cycle
Pyruvate
Coenzyme A
CO2
Transport protein

17. The Acetyl Co-A enters the Citric Acid Cycle in the matrix of the mitochondria.
The Citric Acid cycle breaks down the Acetyl Co-A in a series of steps, releasing CO2
It produces 1 ATP, 3 NADH, and 1 FADH2 per turn.

18. The Citric Acid Cycle
The Citric Acid cycle (also called the Krebs Cycle) has eight steps, each catalyzed by a specific enzyme
The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate (Citric Acid).
The next seven steps decompose the citrate (Citric Acid) back to oxaloacetate, making the process a cycle
Oxaloacetate + Acetyl CoA
Citric Acid

19. The Citric Acid Cycle: Acetyl CoA Oxaloacetate Malate Citrate
CoA—SH
NADH
+H+ 1
H2O
NAD+ 8
Oxaloacetate 2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle
NADH 3 7
+ H+
H2O
CO2
Fumarate
CoA—SH
-Keto-
glutarate
Figure 9.12 A closer look at the citric acid cycle 4 6
CoA—SH
FADH2 5
CO2
NAD+
FAD
Succinate P
NADH i
GTP
GDP
Succinyl
CoA
+ H+
ADP
ATP

20. Each Citric Acid Cycle only produces 1 ATP molecule
Each Citric Acid Cycle only produces 1 ATP molecule. The rest of the energy from pyruvate is in the NADH and FADH2.
The NADH and FADH2 produced by the Citric Acid cycle relay electrons extracted from food to the electron transport chain.

21. The electron transport chain is in the cristae of the mitochondrion
Most of the chain’s components are proteins, which exist in multiprotein complexes
The carriers alternate reduced and oxidized states as they accept and donate electrons
Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O
Oxygen is the final electron acceptor.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

22. The Electron Transport Chain
NADH 50 2 e–
NAD+
FADH2 2 e–
FAD
Multiprotein
complexes  40
FMN
FAD 
Fe•S
Fe•S Q

Cyt b
Fe•S 30
Cyt c1 IV
Free energy (G) relative to O2 (kcal/mol)
Cyt c
Cyt a
Cyt a3 20
Figure 9.13 Free-energy change during electron transport 10 2 e–
(from NADH
or FADH2)
2 H+ + 1/2 O2
H2O

23. Electrons are transferred from NADH or FADH2 to the electron transport chain
Electrons are passed through a number of proteins to O2
The chain’s function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts

24. Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space
H+ then moves back across the membrane, passing through channels in ATP synthase
Animation:

25. ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP
This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work

26. Chemiosmosis couples the electron transport chain to ATP synthesis
Protein complex
of electron
carriers
Cyt c V Q
 
ATP synthase 
2 H+ + 1/2O2
H2O
FADH2
FAD
NADH
NAD+
Figure 9.16 Chemiosmosis couples the electron transport chain to ATP synthesis
ADP + P
ATP i
(carrying electrons
from food) H+ 1
Electron transport chain 2
Chemiosmosis
Oxidative phosphorylation

27. During cellular respiration, most energy flows in this sequence:
glucose  NADH  electron transport chain  proton-motive force  ATP
About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP
+ 6 O2
6CO2 + 6H2O + 38 ATP

28. ATP Yield per molecule of glucose at each stage of cellular respiration:
CYTOSOL
Electron shuttles
span membrane
MITOCHONDRION
2 NADH or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
Glycolysis
Oxidative
phosphorylation:
electron transport
and
chemiosmosis 2
Pyruvate 2
Acetyl
CoA
Citric
acid
cycle
Glucose
+ 2 ATP
+ 2 ATP
+ about 32 or 34 ATP
Figure 9.17 ATP yield per molecule of glucose at each stage of cellular respiration
About
36 or 38 ATP
Maximum per glucose: