1. Chapter 8
Harvesting Energy: Glycolysis and Cellular Respiration

2. Photosynthesis Provides the Energy Released by Glycolysis and Cellular Respiration
ATP
H2O O2
CO2
C6H12O6
glycolysis
photosynthesis
energy from sunlight
cellular
respiration 6
6 CO2 + 6 H2O + light energy  C6H12O6 + 6 O2
Almost all organisms, including those that photosynthesize, use glycolysis and cellular respiration to break down glucose and capture some of the energy as ATP.
Fig. 8-1

3. How Do Cells Obtain Energy?
An overview of glucose breakdown
The overall equation for the complete breakdown of glucose is
C6H12O O2  6 CO H2O + ATP + heat

4. How Do Cells Obtain Energy?
An overview of Glycolysis
The first stage of glucose breakdown is glycolysis
Splitting of glucose (a six-carbon sugar) into two molecules of pyruvate (a three-carbon sugar)
Two ATP molecules are produced
Glycolysis proceeds in the same way under aerobic (with oxygen) or anaerobic (without oxygen) conditions
Glycolysis occurs in the cytoplasm

5. How Do Cells Obtain Energy?
An overview of Cellular Respiration
The second stage of glucose breakdown is aerobic respiration and occurs when oxygen is available
Two pyruvate molecules are broken down into six carbon dioxide molecules and six water molecules
For every two pyruvate molecules, an additional 34 or 36 ATP molecules are generated
Cellular respiration occurs in mitochondria

6. How Do Cells Obtain Energy?
An overview of Aerobic fermentation
If oxygen is not available, the second stage of glucose breakdown is fermentation
Fermentation does not produce any ATP
Pyruvate remains in the cytoplasm and is converted into lactate or ethanol + CO2

7. A Summary of Glucose Breakdown
(cytoplasmic
fluid)
glucose
glycolysis 2
ATP
lactate
2 pyruvate
fermentation
ethanol +
CO2
If O2 is available
If no O2 is available 6 O2
cellular
respiration 34 or 36
ATP 6
CO2 6
H2O
mitochondrion
Fig. 8-2

8. What Happens During Glycolysis?
Glucose activation
A glucose molecule is activated when it receives two phosphates from two ATPs, becoming fructose bisphosphate
Two ATPs are converted into two low-energy adenosine diphosphate (ADP) molecules

9. What Happens During Glycolysis?
Energy harvesting
The six-carbon fructose bisphosphate is split into two, three-carbon molecules of glyceraldehyde-3-phosphate (G3P)
In a series of reactions, each of the two G3P molecules is converted into a pyruvate, generating two ATPs per conversion, for a total of four ATPs
As each G3P is converted to pyruvate, two high-energy electrons and a hydrogen ion are added to an “empty” electron-carrier nicotinamide adenine dinucleotide (NAD+) to make the high-energy electron-carrier molecule NADH

10. The Essentials of Glycolysis
Summary of Glycolysis
Each molecule of glucose is broken down to two molecules of pyruvate
A net of two ATP molecules and two NADH are produced
glucose
fructose
bisphosphate
G3P
pyruvate
NAD+
ADP
ATP 2 4
NADH
Energy harvest
Glucose activation C P 1
Fig. 8-3

11. What Happens During Cellular Respiration?
Cellular respiration in eukaryotic cells occurs in mitochondria in three stages
Pyruvate is broken down in the mitochondrial matrix,
Keep in mind that each glucose molecule produces two pyruvate molecules
High-energy electrons travel through the electron transport chain
ATP is generated by
chemiosmosis
outer membrane
inner membrane
intermembrane space
matrix

12. What Happens During Cellular Respiration?
Mitochondria matrix reactions
The formation of acetyl CoA
Pyruvate is split, forming an acetyl group and releasing CO2
The acetyl group reacts with Coenzyme A, forming acetyl CoA
During this reaction, two high-energy electrons and a hydrogen ion are transferred to NAD+, forming NADH

13. What Happens During Cellular Respiration?
Mitochondria Matrix reactions
The Krebs cycle / Citric Acid cycle
Acetyl CoA is combined with a four-carbon molecule to form six-carbon citrate, and coenzyme A is released
Enzymes in the matrix break down the acetyl group, releasing two CO2 molecules and regenerating the four-carbon molecule for use in future cycles
Each acetyl group produces one ATP, three NADH, and one FADH2

14. Reactions in the Mitochondrial Matrix1
Formation of
acetyl CoA 3
NADH 3
NAD+
FAD
FADH2 C
CO2
coenzyme A
coenzyme A
CO2 is generated as a waste product which diffuses into your blood and exhaled from lungs. C C –
CoA 2
Krebs
cycle C C C 2 C
CO2
acetyl CoA
pyruvate
NAD+
NADH
ADP
Fig. 8-5
ATP

15. What Happens During Cellular Respiration?
Membrane reactions
Electron transport chain (ETC)
10 NADH and 2 FADH for one glucose molecule
These high-energy electrons jump from molecule to molecule in the ETC, losing small amounts of energy at each step
The energy-depleted electrons are transferred to oxygen, which acts as a final electron acceptor
Energy-depleted electrons, oxygen, and hydrogen ions combine to form water
1 water molecule is produced for every 2 electrons.
Without oxygen, electrons would be unable to move through the ETC, and H+ would not be pumped across the inner membrane.
Most eukaryotic cells would die within minutes without a steady supply of oxygen.

16. What Happens During Cellular Respiration?
Chemiosmosis
This energy is harnessed to pump H+ into the intermembrane space, producing a high concentration of H+
The energy is then captured in the bonds of ATP as H+ flows down its gradient
The flow of H+ through the synthase channel provides the energy to synthesize 32 or 34 molecules of ATP for each molecule of glucose e– 2  H+
H2O O2 1
FAD
ATP
FADH2
NAD+
NADH P
ADP
(intermembrane space)
(inner
membrane)
ETC
(matrix)
synthase 3 4
Works like the ETCs of the thylakoid membranes of chloroplasts.
The newly formed ATP leaves the mitochondrion and enters the cytoplasm, where it provides the energy needed by the cell

17. Summary of Cellular Respiration in Eukaryotic cells
Krebs
cycle
electron transport chain
glucose
glycolysis
2 acetyl CoA
CoA
2 pyruvate
(cytoplasmic
fluid)
NADH 32 or 34
FADH2
ATP
total: 36 or 38 ATP
CO2 2 6 4
H2O O2
mitochondrion
Fig. 8-7
Summary of Cellular Respiration in Eukaryotic cells
Lipids and proteins can also be used by converting them to pyruvate or acetyl CoA
The reason two different numbers exist for ATP synthesis is that some cell types have to expend two ATPs to transport the two NADH molecules created during glycolysis into the mitochondrion; others are more efficient and don’t require two

18. What Happens During Fermentation?
Why is anaerobic fermentation necessary?
For glycolysis to continue, the NAD+ used to generate NADH must constantly be regenerated
Under anaerobic conditions, with no oxygen to allow the ETC to function, the cell must regenerate the NAD+ for glycolysis using fermentation in cytoplasm
If the supply of NAD+ were to be exhausted, glycolysis would stop, energy production would cease, and the organism would rapidly die

19. What Happens During Fermentation?
Why is fermentation necessary?
Organisms use one of two types of fermentation to regenerate NAD+
Lactic acid fermentation produces lactic acid from pyruvate
Alcohol fermentation generates alcohol and CO2 from pyruvate

20. What Happens During Fermentation?
Some cells ferment pyruvate to form lactate
Active muscle cells regenerate NAD+ by fermenting pyruvate to lactate, using electrons from NADH and hydrogen ions
A variety of microorganisms that lack mitochondria, including the bacteria that convert milk into yogurt, sour cream, and cheese
NADH
NAD+
glucose 2
ATP
ADP
pyruvate
lactate
(fermentation)
(glycolysis) C r n e g a t i o
When oxygen is available again, muscle cells and the liver can convert lactate into pyruvate.
Fig. 8-8

21. What Happens During Fermentation?
Some cells ferment pyruvate to form alcohol and carbon dioxide
Many microorganisms, such as yeast
During alcohol fermentation, H+ and electrons from NADH are used to convert pyruvate into ethanol and CO2; this releases NAD+, which can accept more high-energy electrons during glycolysis
NADH
NAD+
glucose 2
ATP
ADP
pyruvate
ethanol
CO2
(fermentation)
(glycolysis)
+ 2 C r n e g a t i o
As in lactic acid fermentation, the NAD+ must be regenerated to allow glycolysis to continue
Used to make wine, bread, and sauerkraut