1. Cellular Respiration and Fermentation

2. Overview: Life Is Work
Living cells require energy from outside sources.
Some animals, such as the chimpanzee, obtain energy by eating plants, and some animals feed on other organisms that eat plants.
Examples: assembling polymers, pumping across membrane, moving, reproducing.

3. How do these leaves power the work of life for this chimpanzee?
Energy in organic molecules in food comes from the sun. Energy is recycled.

4. Energy flows into an ecosystem as sunlight and leaves as heat.
Photosynthesis generates O2 and organic molecules, which are used in cellular respiration.
Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work.

5. Photosynthesis in chloroplasts Cellular respiration in mitochondria
Light Energy
Light energy
ECOSYSTEM
Photosynthesis in chloroplasts
 O2
Organic molecules
CO2  H2O
Cellular respiration in mitochondria
Energy flows into an ecosystem as sunlight and ultimately leaves as heat, while the chemical elements essential to life are recycled.
ATP powers most cellular work
ATP
Heat energy
Heat Energy

6. Catabolic pathways yield energy by oxidizing organic fuels
Organic compounds store energy in the arrangement of atoms.
With the help of enzymes, the cell breaks down large molecules that are rich in potential energy.
Some of this energy can be used to perform cellular activities, the rest is lost as heat.
Several processes are central to cellular respiration and related pathways.

7. Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic.
Fermentation is a partial degradation of sugars that occurs without O2.
Aerobic respiration consumes organic molecules and O2 and yields ATP.
Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2.
DEG-RA-DATION

8. C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration.
Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose.
Organic Compounds + Oxygen  Carbon Dioxide + Water + Energy
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
In eukaryotic cells, the mitochondria is home to the metabolic equipment for CR.
Breakdown of glucose is exergonic (-686 kcal/mole of glucose decomposed).
Catabolic Pathways do not directly perform work (flagella), they need energy (regenerated ATP).

9. Redox Reactions: Oxidation and Reduction
Why do the catabolic pathways that decompose glucose and other organic fuels yield energy?
The transfer of electrons during chemical reactions releases energy stored in organic molecules.
This released energy is ultimately used to synthesize ATP.
To understand how CR accomplishes the regeneration of ATP, we have to learn about redox reactions.

10. The Principle of Redox
Chemical reactions that transfer electrons between reactants are called oxidation- reduction reactions, or redox reactions.
In oxidation, a substance loses electrons, or is oxidized.
In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced).

11. becomes oxidized (loses electron) becomes reduced (gains electron)
Consider the reaction between sodium (Na) and chlorine (Cl) that forms table salt.
becomes oxidized (loses electron)
becomes reduced (gains electron)
Figure 9.UN01 In-text figure, p. 164
becomes oxidized
becomes reduced

12. The electron donor is called the reducing agent (X).
becomes oxidized
becomes reduced
The electron donor is called the reducing agent (X).
The electron receptor is called the oxidizing agent (Y).
Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds
An example is the reaction between methane and O2
Xe- becomes oxidized by losing its electron (reducing agent).
Y oxidizes X by removing its electron.
Electron transfer ALWAYS requires a donor and an acceptor, oxidation and reduction always go together.

13. Methane (reducing agent) Oxygen (oxidizing agent)
Reactants
Products
Energy
Water
Carbon dioxide
Methane (reducing agent)
Oxygen (oxidizing agent)
becomes oxidized
becomes reduced
The reaction between methane and oxygen releases energy to the surroundings.
This occurs because the electrons lose potential energy when they end up closer to electronegative atoms such as oxygen.
Electrons end up further from the Carbon atom and closer to oxygen.
The carbon atom has partially “lost” its shared electrons, thus, methane has been oxidized.
The O2 atoms share electrons, but in water, the electrons stick close to the oxygen.
OXYGEN IS ONE OF THE MOST POTENT OXIDIZING AGENTS because it is so electronegative.
Energy must be added to pull electrons away from atoms.

14. Oxidation of Organic Fuel Molecules During Cellular Respiration
The energy yielding process that is most important to us is cellular respiration.
During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced.
becomes oxidized
becomes reduced
Organic molecules that have an abundance of hydrogen are excellent fuels because their bonds are full of electrons whose energy can be released.
The oxidation of glucose produces energy that can be used to create ATP.
Carbs, and fats are packed with electrons associated with H. This H is held back by the “hump” of activation energy.
When glucose is swallowed, enzymes lower the Ea, allowing sugar to be oxidized (steps).
*The status of electrons changes as H is transferred to O, releasing energy.

15. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
In cellular respiration, glucose and other organic molecules are broken down in a series of steps.
Electrons from organic compounds (food) are usually first transferred to NAD+, a coenzyme.
As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration.
NAD+ traps electrons from glucose using the enzyme dehydrogenase.
Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP.
NAD (nicotinamide adenine dinucleotide).

16. Nicotinamide Adenine dinucleotide
Nicotinamide (oxidized form)
NAD
(from food)
Dehydrogenase
Reduction of NAD
Oxidation of NADH
Nicotinamide (reduced form)
NADH
Nicotinamide Adenine dinucleotide
NAD+
Electrons from organic compounds (food) are usually first transferred to NAD+, a coenzyme.
As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration.
NAD+ traps electrons from glucose using the enzyme dehydrogenase.
Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP.

17. NADH passes the electrons to the electron transport chain.
Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction.
O2 pulls electrons down the chain in an energy-yielding tumble.
The energy created is used to regenerate ATP

18. Food  NADH  ETC  Oxygen
(a) Uncontrolled reaction
(b) Cellular respiration
Explosive release of heat and light energy
Controlled release of energy for synthesis of ATP
Free energy, G
H2  1/2 O2
2 H 
1/2 O2
H2O
2 H+  2 e
2 e
2 H+
ATP
Electron transport chain
(from food via NADH)
ETC
Hydrogen and Oxygen combining to form water is an uncontrolled, exergonic reaction. A large amount of heat and light energy is released (explosion).
In CR, the same reaction occurs in stages. An ETC breaks the sudden reaction into a series of smaller steps and stores some released energy to make ATP (rest is released as heat).
Food  NADH  ETC  Oxygen

19. The Stages of Cellular Respiration: A Preview
Harvesting of energy from glucose has three stages:
Glycolysis (breaks down glucose into two molecules of pyruvate).
The citric acid cycle (completes the breakdown of glucose).
Oxidative phosphorylation (accounts for most of the ATP synthesis).

20. The Stages of Cellular Respiration
Glycolysis (color-coded teal throughout the chapter) 1.
Pyruvate oxidation and the citric acid cycle (color-coded salmon) 2.
Oxidative phosphorylation: electron transport and chemiosmosis (color-coded violet) 3.

21. During Glycolysis, each glucose molecule is broken down into two molecules of the compound pyruvate.
Pyruvate enters mitochondrion, where the citric acid cycle oxidizes it into carbon dioxide.
NADH and a similar coenzyme called FADH2 transfer electrons from glucose to the ETCs, which are built into the mitochondrial membrane.
During oxidative phosphorylation, ETCs convert chemical energy to a form used for ATP synthesis in a process called chemiosmosis.
The process that generates most of the ATP is oxidative phosphorylation because it is powered by redox reactions.

22. Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation.
For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 38 molecules of ATP.
Each has 7.3 kcal/mol of free energy.

23. During substrate-level phosphorylation,
Product
ADP P
ATP
Enzyme
During substrate-level phosphorylation,
some ATP is made by direct enzymatic transfer of a phosphate group from an organic substrate to ADP.

24. Check yourself!
In the following redox reaction, which compound is oxidized and which is reduced? C4H6O5 + NAD+  C4H4O5 + NADH + H+
C4H6O5 is oxidized and NAD+ is reduced.

25. Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate.
Glycolysis occurs in the cytoplasm and has ten steps and two major phases:
Energy investment phase
Energy payoff phase
Glycolysis occurs whether or not O2 is present.

26. Glycolysis: Energy Investment Phase
ATP
Glucose
Glucose 6-phosphate
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Dihydroxyacetone phosphate
Glyceraldehyde 3-phosphate
To step 6
ADP
Hexokinase
Phosphogluco- isomerase
Phospho- fructokinase
Aldolase
Isomerase 1 2 3 4 5
GLUCOSE is phosphorylated by ENZYME 1, gaining a phosphate group from ATP . The Pi group is charged and traps the sugar in the cell.
Glucose-6-phosphate is rearranged by ENZYME 2 and converted to fructose-6-phosphate.
ENZYME 3 transfers the Pi group from ATP to fructose… (using a second ATP). The sugar can now be spilt in half.
ENZYME 4 cleaves the sugar into two different 3 carbon sugars.
ENZYME 5 catalyzes the conversion between the two sugars (never reaches equilibrium because the next step in glycolysis only uses glyceraldehyde).
Glyceraldehyde moves on to the next stage of glycolysis.

27. After the sugar splits, every reaction is doubled!
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
2 NAD
+ 2 H
2 P i
2 ADP
1,3-Bisphospho- glycerate
3-Phospho- glycerate
2-Phospho- glycerate
Phosphoenol- pyruvate (PEP)
Pyruvate 2
2 H2O
Phospho- glycerokinase
Phospho- glyceromutase
Enolase
Pyruvate kinase 6 7 8 9 10
Triose phosphate dehydrogenase
6. ENZYME 6 oxidizes the glyceraldehyde by transferring e-’s, 2 H+, and NAD+, forming 2 NADH (redox). This is highly exergonic and the enzyme uses the energy to attach a Pi group to the substrate (storing energy)!
7. Some ATP is produced by substrate-level phosphorylation. The 2 ATP that were used in the first phase have been repaid.
8. ENZYME 7 relocates the remaining Pi group. Preparing the substrate for the next reaction.
9. ENZYME 8 causes a double bond in the substrate by extracting WATER (creating phosphoenolpyruvate PEP). Electrons in substrate are rearranged so that the Pi becomes unstable.
10. ENZYME 9 uses the last Pi group and the PEP to create another 2 ATP.
-If oxygen is present, the chemical energy in 2 pyruvate can be extracted by the citric acid cycle.
Overall, glycolysis uses 2 ATP in the first phase, but creates 4 ATP in return!

28. CHECK YOURSELF!
Glycolysis: Energy Investment Phase
ATP
Glucose
Glucose 6-phosphate
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Dihydroxyacetone phosphate
Glyceraldehyde 3-phosphate
To step 6
ADP
Hexokinase
Phosphogluco- isomerase
Phospho- fructokinase
Aldolase
Isomerase 1 2 3 4 5
During the redox reaction in glycolysis (step 6), which molecule acts as the oxidizing agent? The reducing agent?
NAD+ is the oxidizing agent, accepting electrons from glyceraldehyde
Glyceraldehyde is the reducing agent.
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
2 NAD
+ 2 H
2 P i
2 ADP
1,3-Bisphospho- glycerate
3-Phospho- glycerate
2-Phospho- glycerate
Phosphoenol- pyruvate (PEP)
Pyruvate 2
2 H2O
Phospho- glycerokinase
Phospho- glyceromutase
Enolase
Pyruvate kinase 6 7 8 9 10
Triose phosphate dehydrogenase

29. All of that only occurred here!
Glycolysis releases less than a quarter of the chemical energy stored in glucose, most remains in the pyruvate.
Net products are: 2 NADH, 2H+, 2 Pyruvate, 2 ATP, 2 H20

30. the citric acid cycle completes the energy-yielding oxidation of organic molecules
In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed.

31. Oxidation of Pyruvate to Acetyl CoA
Before the citric acid cycle can begin, pyruvate must be converted to acetyl Coenzyme A (acetyl CoA), which links glycolysis to the citric acid cycle.
This step is carried out by a multi-enzyme complex that catalyzes three reactions.

32. Pyruvate’s carboxyl group is removed and turned into CO2.
Transport protein
CYTOSOL
MITOCHONDRION
CO2
Coenzyme A
NAD
+ H
NADH
Acetyl CoA 1 2 3
Pyruvate’s carboxyl group is removed and turned into CO2.
The remaining two-carbon fragment is oxidized forming acetate and the electrons are transferred to NAD+  NADH.
Coenzyme A is attached, forming an acetyl group, which is highly reactive.

33. The Citric Acid Cycle
The citric acid cycle, also called the Krebs cycle, completes the break down of pyruvate to CO2
The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn.

34. The Citric Acid Cycle
The citric acid 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.
The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle.
The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain.

35. The Citric Acid Cycle Citric acid cycle Acetyl CoA Oxaloacetate Malate
CoA-SH
NADH
+ H 1
H2O
NAD
Oxaloacetate 8 2
Malate
Citrate
Isocitrate
NAD
Citric acid cycle
NADH 3 7
+ H
H2O
CO2
Fumarate
CoA-SH
-Ketoglutarate
Acetyl CoA adds a 2 carbon acetyl group to starting molecule, producing citrate.
Water is added and extracted to form isocitrate from citrate.
Loses a CO2 and then reduces NAD+ to NADH.
Loses another CO2 and reduces NAD+ to NADH again. Attaches to acetyl CoA (unstable).
CoA displaced by phosphate group, ultimately forming ATP.
2 Hydrogens attach to FAD forming FADH2.
Addition of water rearranges bonds.
Oxidation of NAD+ to NADH, regenerates the original molecule. 4 6
CoA-SH 5
FADH2
CO2
NAD
FAD
Succinate
P i
NADH
GTP
GDP
Succinyl CoA
+ H
ADP
ATP

36. Section Questions
In which molecules is most of the energy form the citric acid cycle's redox reactions conserved? How will these molecules convert their energy to a form that can be used to make ATP?
What cellular processes produce the carbon dioxide that you exhale?
NADH and FADH2; will donate their electrons to the ETC.
CO2 is removed from pyruvate, which is produced by glycolysis, and CO2 is produced by the citric acid cycle.

37. During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food.
These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation.

38. The Pathway of Electron Transport
The electron transport chain is in the inner membrane (cristae) of the mitochondrion.
Most of the chain’s components are proteins, which exist in multi-protein 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.

39. The Pathway of Electron Transport
NADH 50
2 e
NAD
FADH2
2 e
FAD
Multiprotein complexes I 40
FMN II
FeS
FeS Q
III
The Pathway of Electron Transport
Cyt b 30
FeS
Cyt c1 IV
Free energy (G) relative to O2 (kcal/mol)
Cyt c
Cyt a
Cyt a3 20
Overall energy drop (ΔG) for electrons is 53 kcal/mol.
Broken up into a series of smaller “falls” in the ETC.
For every 2 NADH molecules, I O2 molecule is reduced to 2 H2O) 10
2 e
(originally from NADH or FADH2)
2 H + 1/2 O2
H2O

40. The Pathway of Electron Transport
Electrons are transferred from NADH or FADH2 to the electron transport chain.
Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2.
The electron transport chain generates no ATP directly.
It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts.

41. Chemiosmosis: The Energy-Coupling Mechanism
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 the proton, ATP synthase.
ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP.
Chemiosmosis is the use of energy in a H+ gradient to drive cellular work.

42. Chemiosmosis: The Energy-Coupling Mechanism
INTERMEMBRANE SPACE H
Chemiosmosis: The Energy-Coupling Mechanism
Stator
Rotor
Internal rod
Functions as a mill, powered by the flow of H+.
Found in the membranes of mitochondria and chloroplast of eukaryotes and in plasma membrane of prokaryotes.
Each of the 4 parts are made up of polypeptide subunits.
Catalytic knob
ADP +
P i
ATP
MITOCHONDRIAL MATRIX

43. Oxidative phosphorylation
Protein complex of electron carriers H
Cyt c IV Q
III I
ATP synth- ase II
2 H + 1/2O2
H2O
FADH2
FAD
The ETC located inside the mitochondrial membrane.
Yellow: traces the path of electrons, forms water.
H+ pumped into intermembrane space.
Flow back through ATP Synthase, forms ATP
Ox. Phos. Combines ETC and Chemiosmosis.
NAD
NADH
ADP  P i
ATP
(carrying electrons from food) H 1
Electron transport chain 2
Chemiosmosis
Oxidative phosphorylation
Oxidative phosphorylation

44. Oxidative phosphorylation
The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis.
The H+ gradient is referred to as a proton- motive force, emphasizing its capacity to do work

45. An Accounting of ATP Production by Cellular Respiration
During cellular respiration, most energy flows in this sequence:
glucose  NADH  electron transport chain  proton-motive force  ATP
About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32 ATP.
There are several reasons why the number of ATP is not known exactly.
The numbers are not whole numbers.
ATP yield varies depending on electron transport.
Amount of proton-motive force varies.

46. Oxidative phosphorylation: electron transport and chemiosmosis
Electron shuttles span membrane
MITOCHONDRION
2 NADH or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
Oxidative phosphorylation: electron transport and chemiosmosis
Glycolysis
Pyruvate oxidation
Citric acid cycle
Glucose
2 Pyruvate
2 Acetyl CoA
4 ATP produced by glycolysis and ABOUT 26 or 28 by oxidative phosphorylation.
 2 ATP
 2 ATP
 about 26 or 28 ATP
About 30 or 32 ATP
Maximum per glucose:
CYTOSOL
ATP Yield per Molecule of Glucose

47. Section questions
What would occur if O2 was not present in this picture?
In the absence of O2, what do you think would happen if you decreased the pH of the intermembrane space of the mitochondria? Explain.
Ox. Phos. Would stop and no ATP would be produced. Electrons wouldn’t be pulled down the ETC, H+ wouldn’t be pumped, and chemiosmosis would not occur.
Decreasing pH (adding H+) would establish a proton gradient without ETC. ATP synthase would function and create ATP.

48. Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen
Most cellular respiration requires O2 to produce ATP.
Without O2, the electron transport chain will cease to operate.
In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP.

49. CREATING ATP WITHOUT THE USE OF OXYGEN
Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example sulfate.
Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP
Anaerobic: an means “without” and aer means “air”.

50. Types of Fermentation
Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis.
Two common types are:
Alcohol Fermentation
Lactic Acid Fermentation

51. Types of Fermentation
In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2
Alcohol fermentation by yeast is used in brewing, winemaking, and baking

52. Types of Fermentation i i   2 ATP  2 ATP Glucose Glycolysis Glucose
2 ADP  2 P i
2 ATP
2 ADP  2 P i
2 ATP
Glucose
Glycolysis
Glucose
Glycolysis
2 Pyruvate 2
NAD 
2 NADH
2 CO2 2
NAD 
2 NADH 
2 H 
2 H
2 Pyruvate
Produces ethanol
Produces lactate (ionized form of lactic acid)
2 Ethanol
2 Acetaldehyde
2 Lactate
(a) Alcohol fermentation
(b) Lactic acid fermentation

53. Types of Fermentation
In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate as an end product, with no release of CO2.
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt.
Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce.
The lactate that accumulates may cause muscle fatigue and pain.
Lactate is converted back to pyruvate by liver cells.

54. Fermentation Cellular Respiration
1. Produces 2 ATP per Glucose Molecule
2. Pyruvate/Acetaldehyde (final electron acceptor)
Cellular Respiration
1. Produces 32 ATP per Glucose Molecule
2. O2
(final electron acceptor)
Glycolysis
NAD+
(oxidizing agent)
All use glycolysis (net ATP = 2) to oxidize glucose and harvest chemical energy of food.
In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis.
The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration
Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule
COMPARING FERMENTATION & CELLULAR RESPIRATION

55. Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2.
Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration.
In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes.

56. Ethanol, lactate, or other products
Glucose
Glycolysis
CYTOSOL
Pyruvate
No O2 present: Fermentation
O2 present: Aerobic cellular respiration
MITOCHONDRION
Ethanol, lactate, or other products
Acetyl CoA
The “fork” in the road after glycolysis occurs.
Citric acid cycle

57. The Evolutionary Significance of Glycolysis
Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere.
Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP.
Glycolysis is a very ancient process.

58. Section Questions
What is the final acceptor for NADH’s electrons during fermentation? What is the final acceptor for its electrons during respiration?
If a glucose fed yeast cell is moved from an aerobic environment to an anaerobic one, how would its rate of glucose consumption need to change?
Acetaldehyde or Pyruvate, oxygen
It would need to consume glucose at a much faster pace because only 2 ATP are made during fermentation.

59. Glycolysis and the citric acid cycle connect to many other metabolic pathways
Glycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways

60. The Versatility of Catabolism
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration.
Glycolysis accepts a wide range of carbohydrates.
Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle.

61. The Versatility of Catabolism
Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA).
Fatty acids are broken down by beta oxidation and yield acetyl CoA.
An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate.

62. Oxidative phosphorylation
Proteins
Carbohydrates
Fats
Amino acids
Sugars
Glycerol
Fatty acids
Glycolysis
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Acetyl CoA
All 3 can be used as fuel for CR.
Monomers enter glycolysis or citric acid cycle at different points.
Called “funnels” through which electrons” fall” to oxygen.
Citric acid cycle
The Versatility of Catabolism
Oxidative phosphorylation

63. Biosynthesis (Anabolic Pathways)
The body uses small molecules to build other substances.
These small molecules may come directly from food, from glycolysis, or from the citric acid cycle.
They can be converted by cells to other types of molecules.
If we eat more food than we need, we store excess fat.
Metabolism is adaptable.

64. Regulation of Cellular Respiration via Feedback Mechanisms
Feedback inhibition is the most common mechanism for control.
If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down.
Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway.

65. The control of cellular respiration
Glucose
AMP
Glycolysis
Fructose 6-phosphate
Stimulates 
Phosphofructokinase  
Fructose 1,6-bisphosphate
Inhibits
Inhibits
The control of cellular respiration
Pyruvate
ATP
Citrate
Acetyl CoA
Inhibitors and activators help set the pace of glycolysis and the CAC.
One enzyme, phosphofructokinase (step 3 in glycolysis) is stimulated by AMP (from ADP) but inhibited by ATP and citrate.
This adjusts the rate of respiration as the cell’s demands change.
Citric acid cycle
Oxidative phosphorylation

66. Section questions
Compare the structure of a fat with that of a carbohydrate. What features make fat a much better fuel?
Under what circumstances might your body synthesize fat molecules?
What will happen to a muscle cell that has used up its supply of oxygen and ATP?
Fat has many CH2 units, In carb molecules, some of the electrons are already oxidized (bound to oxygen)
Consuming more food than needed. Fat synthesis occurs to store energy for later.
The cell will convert pyruvate to lactate, to make ATP.