1. Cellular Respiration and Fermentation9
Cellular Respiration and Fermentation
Lecture Presentation by Cindy S. Malone, PhD, California State University Northridge

2. Please make sure to highlight all the terms in blue.

3. An Overview of Cellular Respiration
All organisms use glucose to build fats, carbohydrates, and other compounds.
Cells recover glucose by breaking down these molecules.
Glucose is used to make ATP through cellular respiration or fermentation.
Cellular respiration produces ATP from a molecule with high potential energy, usually glucose.

4. An Overview of Cellular Respiration
Each of the four steps of cellular respiration consists of:
A series of chemical reactions
A distinctive starting molecule
Characteristic set of products

5. Starch, glycogen, fats (synthesized from glucose)
Figure 9.1
Energy conversion
Photosynthesis
Energy storage
Starch, glycogen, fats (synthesized from glucose)
Energy use
Figure 9.1 Glucose Is the Hub of Energy Processing in Cells.
Cellular Respiration
Fermentation 5

6. What Happens When Glucose Is Oxidized?
Oxygen atoms in oxygen are reduced to form water:
C6H12O6  6 O2  6 CO2  6 H2O  energy
glucose oxygen carbon water
dioxide
Glucose is oxidized through a long series of carefully controlled redox reactions.
The resulting change in free energy is used to synthesize ATP from ADP and Pi.
These reactions comprise cellular respiration.

7. The Steps of Cellular Respiration
Cellular respiration is:
Any set of reactions that produces ATP
In an electron transport chain
Cellular respiration has four steps:
1. Glycolysis
Glucose is broken down to pyruvate
2. Pyruvate processing
Pyruvate is oxidized to form acetyl CoA

8. The Steps of Cellular Respiration
3. Citric acid cycle
Acetyl CoA is oxidized to CO2
4. Electron transport and chemiosmosis
Compounds reduced in steps 1–3 are oxidized in reactions leading to ATP production

9. Cellular Respiration Interacts with Metabolic Pathways
Energy and carbon:
Are two fundamental requirements of cells.
Need high-energy electrons for generating chemical energy in the form of ATP.
Are a source of carbon-containing molecules for synthesizing macromolecules.
Metabolism includes:
Thousands of different chemical reactions that are either catabolic pathways or anabolic pathways.

10. Cellular Respiration Interacts with Metabolic Pathways
Catabolic pathways
Involve the breakdown of molecules and production of ATP.
Often harvest stored chemical energy to produce ATP.
Anabolic pathways
Result in the synthesis of larger molecules from smaller components.
Often use energy in the form of ATP.

11. Catabolic Pathways Break Down a Variety of Molecules
For ATP production, cells:
First use carbohydrates, then fats and finally proteins.
Proteins, carbohydrates, and fats can all furnish substrates for cellular respiration.

12. Anabolic Pathways Synthesize Key Molecules
Molecules found in carbohydrate metabolism are used to synthesize macromolecules such as:
RNA
DNA
Glycogen or starch
Amino acids
Fatty acids
And other cell components

13. Glycolysis: Processing Glucose to Pyruvate
Glycolysis is:
A series of 10 chemical reactions
The first step in glucose oxidation
All of the enzymes needed for glycolysis are found in the cytosol.
In glycolysis:
Glucose is broken down into two molecules of pyruvate.
The potential energy released is used to phosphorylate ADP to ATP.

14. The Glycolysis Reactions
Glycolysis consists of:
An energy investment phase
An energy payoff phase

15. The Glycolysis Reactions
In the energy investment phase:
2 molecules of ATP are consumed
In the energy payoff phase:
Sugar is split to form two pyruvate molecules
2 molecules of NAD+ are reduced to NADH
4 molecules of ATP are formed by substrate-level phosphorylation (net gain of 2 ATP)

16. Feedback Inhibition Feedback inhibition occurs:
When an enzyme in a pathway is inhibited by the product of that pathway.
Cells that are able to stop glycolytic reactions when ATP is abundant.
Can conserve their stores of glucose for times when ATP is scarce.

17. Feedback Inhibition Regulates Glycolysis
During glycolysis, high levels of ATP inhibit:
The enzyme phosphofructokinase
This enzyme catalyzes one of the early reactions
Phosphofructokinase has two binding sites for ATP:
1. The active site
Where ATP phosphorylates fructose-6-phosphate
Resulting in the synthesis of fructose-1,6-bisphosphate
2. A regulatory site

18. Feedback Inhibition Regulates Glycolysis
High ATP concentrations cause:
ATP to bind at the regulatory site
Changing the enzyme’s shape
Dramatically decreasing the reaction rate at the active site
In phosphofructokinase:
ATP acts as an allosteric regulator

19. ATP at regulatory site ATP at active site
Figure 9.7
When ATP binds here, the reaction rate slows dramatically
ATP at regulatory site
Figure 9.7 Phosphofructokinase Has Two Binding Sites for ATP.
Fructose-6- phosphate at active site
ATP at active site 19

20. The Remaining Reactions Occur in the Mitochondria
Pyruvate produced during glycolysis is:
Transported from the cytosol
Into the mitochondria
Mitochondria have both inner and outer membranes.
Cristae:
Are layers of sac-like structures that fill the interior of the mitochondria.
The mitochondrial matrix:
Is inside the inner membrane
But outside the cristae

21. Inner membrane Intermembrane space Outer membrane
Figure 9.8
Cristae are sacs of inner membrane joined to the rest of the inner membrane by short tubes
Matrix
Cristae
Inner membrane
Intermembrane space
Figure 9.8 The Structure of the Mitochondrion.
Outer membrane
100 nm 21

22. Pyruvate Processing Pyruvate processing is: In the presence of O2:
The second step in glucose oxidation
Catalyzed by the enzyme pyruvate dehydrogenase in the mitochondrial matrix.
In the presence of O2:
Pyruvate undergoes a series of reactions, results in the product molecule acetyl coenzyme A (acetyl CoA)

23. Pyruvate Acetyl CoA Figure 9.9
Figure 9.9 Pyruvate Is Oxidized to Acetyl CoA.
Pyruvate
Acetyl CoA 23

24. The Citric Acid Cycle The third step of glucose oxidation:
The acetyl CoA produced by pyruvate processing enters the citric acid cycle.
Located in the mitochondrial matrix
Each acetyl CoA is oxidized to two molecules of CO2
Some of the potential energy released is used to:
1. Reduce NAD+ to NADH
2. Reduce flavin adenine dinucleotide (FAD) to FADH2
Another electron carrier
3. Phosphorylate GDP to form GTP
Later converted to ATP

25. runs twice for each glucose molecule oxidized
Figure 9.10
The two red carbons enter the cycle via acetyl CoA
All 8 reactions of the citric acid cycle occur in the mitochondrial matrix, outside the cristae
Acetyl CoA
Citrate
Isocitrate
In each turn of the cycle, the two blue carbons are converted to CO2
-Ketoglutarate
Oxaloacetate
The CITRIC ACID CYCLE
runs twice for each glucose molecule oxidized
Figure 9.10 The Citric Acid Cycle Completes the Oxidation of Glucose.
In the next cycle, this red carbon becomes a blue carbon
Succinyl CoA
Malate
Each reaction is catalyzed by a different enzyme
Succinate
Fumarate 25

26. The Citric Acid Cycle Regulation and Summary
The citric acid cycle can be turned off at multiple points via several different mechanisms of feedback inhibition.
Citric acid cycle starts with acetyl CoA and ends with CO2.
The potential energy that is released is used to produce NADH, FADH2, and ATP.
When energy supplies are high the cycle slows down.

27. This step is regulated by ATP
Figure 9.11
These steps are also regulated via feedback inhibition, by NADH and ATP
This step is regulated by ATP
Figure 9.11 The Citric Acid Cycle Is Regulated by Feedback Inhibition. 27

28. Glucose Oxidation Summary
Glucose oxidation produces:
ATP, NADH, FADH2, and CO2
Glucose is completely oxidized to:
Carbon dioxide via glycolysis
The subsequent oxidation of pyruvate
Then the citric acid cycle
In eukaryotes, glycolysis occurs in the cytosol.
Pyruvate oxidation and the citric acid cycle take place in the mitochondrial matrix.

29. Figure 9.12
Figure 9.12 Glucose Oxidation Produces ATP, NADH, FADH2, and CO2.
Cytosol
Mitochondrial matrix 29

30. Free Energy Changes, NADH, and FADH2
Each glucose molecule that is oxidized to 6 CO2:
Reduces 10 molecules of NAD+ to NADH
2 molecules of FAD to FADH2
Produces 4 molecules of ATP
By substrate-level phosphorylation
The ATP can be used directly for cellular work.
Most of glucose’s original energy is contained in:
The electrons transferred to NADH and FADH2
Which then carry them to oxygen, the final electron acceptor.

31. Free-energy change relative to glucose (kcal/mol)
Figure 9.13
GLYCOLYSIS
PYRUVATE PROCESSING
CITRIC ACID CYCLE
Free-energy change relative to glucose (kcal/mol)
In each of these drops, energy is transferred to energy-storing molecules ATP, NADH, GTP, or FADH2
Figure 9.13 Free Energy Changes as Glucose Is Oxidized.
Oxidation of glucose  31

32. The Electron Transport Chain
During the fourth step in cellular respiration:
The high potential energy of the electrons carried by NADH and FADH2 is gradually decreased as they move through a series of redox reactions.
The proteins involved in these reactions make up:
An electron transport chain (ETC)
O2 is the final electron acceptor
The transfer of electrons along with protons to oxygen forms water.

33. Free-energy change relative to O2 (kcal/mol)
Figure 9.14
Complex I
Complex II
ETC reactions
take place in the inner membrane and cristae of the mitochondrion
Complex III
Free-energy change relative to O2 (kcal/mol)
Complex IV
Figure 9.14 A Series of Reduction–Oxidation Reactions Occur in an Electron Transport Chain.
FMN: flavin-containing prosthetic group in flavoprotein
FeS: protein with an iron–sulfur cofactor
Cyt: protein with a heme prosthetic group
Q: ubiquinone, a nonprotein coenzyme
Reduction-oxidation reactions  33

34. ATP Yield from Cellular Respiration
The vast majority of the “payoff” from glucose oxidation occurs via oxidative phosphorylation.
ATP synthase produces:
25 of the 29 ATP molecules
Produced per glucose molecule during cell respiration

35. Figure 9.19
Electron transport chain
Oxidative phosphorylation
Electrons
Figure 9.19 ATP Yield during Cellular Respiration.
Maximum yield of ATP per molecule of glucose: 29
Cytosol
Mitochondrial matrix 35

36. Aerobic and Anaerobic Respiration
All eukaryotes and many prokaryotes use:
Oxygen as the final electron acceptor
Of electron transport chains in aerobic respiration
Some prokaryotes:
Especially those in oxygen-poor environments
Use other electron acceptors in anaerobic respiration

37. Fermentation Cellular respiration cannot occur without oxygen.
Metabolic pathway that regenerates NAD+ from NADH
Glycolysis can produce ATP in the absence of oxygen
Fermentation occurs:
When pyruvate or a molecule derived from pyruvate
Accepts electrons from NADH
This transfer of electrons oxidizes NADH to NAD+:
Glycolysis can continue to produce ATP
Via substrate-level phosphorylation

38. Different Fermentation Pathways
In lactic acid fermentation:
Pyruvate produced by glycolysis
Accepts electrons from NADH
Lactate and NAD+ are produced
Lactic acid fermentation occurs in muscle cells
In alcohol fermentation:
Pyruvate is enzymatically converted to acetaldehyde and CO2
Acetaldehyde accepts electrons from NADH
Ethanol and NAD+ are produced
Alcohol fermentation occurs in yeast

39. Please make sure to read the corresponding textbook chapter.