Cellular respiration involves the breakdown of glucose to release energy through a series of redox reactions. There are four stages: glycolysis, the preparatory reaction, the Krebs cycle, and the electron transport chain. These stages occur in both the cytoplasm and mitochondria, with oxygen as the final electron acceptor. The process generates approximately 38 ATP per glucose molecule through oxidative phosphorylation. When oxygen is limited, fermentation allows limited ATP production without oxygen.

1. Chapter 7
Pathways of Cellular Respiration

2. Glucose breakdown releases
energy
Cellular respiration is a redox reaction that requires C 6H12O6
and O2
• Oxidation
– Removal of H+
• Reduction
– Addition of H+
• Glucose is oxidized to CO2
• Oxygen is reduced to H2O
• Oxidation of glucose to CO2 releases energy, which is
then used for ATP production

3. • NAD+ (nicotinamide adenine dinucleotide) and
FAD (flavin adenine dinucleotide) are coenzmes
that aid in glucose oxidation
• (NAD+) + (2e-) + (H+)  NADH
• (FAD) + (2e-) + (2H+)  FADH2
• The high energy electrons in NADH and FADH2
are taken to the electron transport chain within a
mitochondrion
• O2 picks up electrons at the end of the chain,
then takes on H+ to become H2O
• NAD+ and FAD return to pick up more electrons

4. Cellular respiration involves the
cytoplasm and mitochondria
4 stages of cellular respiration
• Glycolysis
– In cytoplasm
– No oxygen required
(anaerobic)
• Preparatory reaction
– In mitochondria matrix
– Requires oxygen (aerobic)
• Krebs cycle
– In mitochondria matrix
– Requires oxygen (aerobic)
• Electron transport chain (ETC)
– In mitochondria cristae
– Requires oxygen (aerobic)
A: intermembrane space
In aerobic phases, oxygen is the
final acceptor of electrons B: matrix
C: cristae

5. Oxidation of glucose
• Glycolysis
– Glucose is broken into 2 molecules of pyruvate
– NADH produced
– Net 2 ATP produced
• Preparatory reaction
– Pyruvate oxidized (loses H+) releasing CO2
– NADH produced
– End product – 2, 2 carbon acetyle groups
• Krebs cycle (citric acid cycle)
– Oxidation of glucose products
– NADH and FADH2 result
– CO2 released
– 2 ATP produced per glucose molecule

6. Production of most ATP
• Electron transport chain
– NADH and FADH2 bring high energy electrons
– As electrons go down chain, energy is
released and captured
– O2 accepts electrons at the end of the chain,
which then combines with H+ to form H2O

7. The chemical energy of glucose
becomes the chemical energy of ATP
Glycolysis: Glucose breakdown begins
• Occurs in cytoplasm
• No oxygen required
Energy investment steps
• 2 ATP breaks glucose into 2 G3P
molecules

8. Energy harvesting steps
• G3P oxidized (H+ removed)
• H+ combines with NAD+ to create NADH
– 2 high energy electrons on NADH
• P attaches to the oxidized G3P
• P is added to ADP to create ATP
• ATP synthesis occurs again
• 2 pyruvate and 2 ATP are final products

10. The preparatory reaction occurs
before the Krebs cycle
• The preparatory reactions
– In mitochondria matrix
– Pyruvate is oxidized (H+ removed) creating an acetyl group
– H+ taken up by NAD+ to form NADH
– Acetyl group combines with CoA and goes to the Krebs cycle
– NADH goes to electron transport chain
– CO2 leaves the body

11. The Krebs cycle generates much
NADH
• In matrix
• Acetyle group removed from CoA
• Acetyl group joins a 4-carbon group to create citrate
• Citrate oxidized (H+ removed)
– NADH created
– CO2 created
• 2 ATP formed
• FAD oxidized to form FADH2
• 4 CO2, 6 NADH, 2 FADH2, and 2 ATP are final products
• FADH2 and NADH goes to electron transport chains

13. The electron transport chain
captures energy for ATP production
• In mitochondria cristae
• NADH and FADH2 release electrons and H+
– Electrons energy electron transport chain
– NAD+ and FAD result
• Electrons release energy as they go down chain,
which is used to make ATP
• Electrons combine with O2 and H+ to form H2O
• 3 ATP produced per NADH (30 ATP total)
• 2 ATP produced per FADH2 (4 ATP total)

14. The ATP synthase complex
produces ATP
• Hydrogen pumped to intermembrane space from NADH
and FADH2 creating a concentration gradient
• Hydrogen then moves down the gradient into matrix via
H+ channel protein
• ATP synthase enzyme is attached to H+ channel protein
and produces ATP as H+ passes through protein
• ATP leaves mitochondria to go to where it is needed

15. The ATP payoff can be calculated
• In the cytoplasm
– Glycolysis
• 2 ATP
• In the mitochondria
– Preparatory reaction
• No ATP produced
– Krebs cycle
• 2 ATP
– Electron transport chain
• 32 or 34 ATP
• 3 ATP per NADH
• 2 ATP per FADH2
• In many animals NADH formed in glycolysis cannot cross inner
mitochondrial membrane so 1 ATP per NADH is used to move them
across
Glucose breakdown results in 36 or 38 ATP
39% of available energy in glucose is transferred to ATP,
the rest of the energy is lost as heat

16. http://media.pearsoncmg.com/bc/bc_0media_bio/bioflix/bioflix.htm?cc5respiration

17. Fermentation is inefficient
When oxygen is in short supply,
the cell switches to
fermentation
• 2 ATP produced per glucose
molecule
• In animals: pyruvate accepts
electrons and is reduced to
lactate
• In other organisms: alcohol
and CO2 are produces

18. • Benefits versus drawbacks of fermentation
– Can occur without oxygen
– Provide quick bursts of energy (important for
muscle cells)
– Products are toxic to cells
• Yeast produces alcohol, but it kills them (wine)
• Lactate builds up in muscle cells, which changes
the cell pH and causes the “burn”
– The liver can convert lactate back to pyruvate
so cellular respiration can produce the
remaining ATP

19. Metabolic pathways cross at
particular substrates
Organic molecules can be broken down and
synthesized as needed
• Catabolism – breaking down of molecules
– Fats are a glycerol (can enter glycolysis) and 3 fatty
acids (can convert to acetyl CoA and energy the
Krebs cycle)
– Carbon skeleton of amino acids can enter glycolysis,
be converted to acetyle CoA, or enter the Krebs cycle
directly
• Anabolism – building up of molecules
– G3P from glycolysis can be converted to glycerol,
acetyl groups from the preparatory reactions can be
joined to form fatty acids, fat synthesis follows, which
can lead to weight gain

20. Essential Amino Acids
• Plants are able to produce all the amino
acids they need
• Animals can only produce 11 of 20
essential amino acids because they lack
some enzymes for synthesis of the other 9
amino acids. These amino acids are
required in the diet of animals or protein
deficiency will result.