1. Figure 9.1 How do these leaves power the work of life for the giant panda?

2. Energy flows into an ecosystem as sunlight and leaves as heat
Photosynthesis makes O2 and organic molecules (like sugars and proteins), which are used in cellular respiration
Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work
The process by which cells break down organic molecules (food) to make ATP is called cellular respiration
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3. Organic molecules Cellular respiration in mitochondria
Fig. 9-2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
molecules
CO2 + H2O
+ O2
Cellular respiration
in mitochondria
Figure 9.2 Energy flow and chemical recycling in ecosystems
ATP
ATP powers most cellular work
Heat
energy

4. Catabolic Pathways and Production of ATP
The breakdown of organic molecules such as glucose is exergonic (releases free energy used to power ADP + Pi  ATP)
Aerobic respiration breaks down organic molecules completely with the help of O2 and generates lots of energy for making ATP
Fermentation is a partial breakdown of sugars that occurs without O2 and makes only a small amount of ATP
Aerobic exercise makes you breathe hard- you’re using up a lot of oxygen!
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5. Cellular respiration technically includes both aerobic and anaerobic respiration but usually refers to aerobic respiration
Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy
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6. Redox Reactions: Oxidation and Reduction
The transfer of electrons during chemical reactions releases energy stored in organic molecules
This released energy is ultimately used to synthesize ATP
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7. 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 (its charge becomes reduced, more negative)
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8. becomes oxidized (loses electron) becomes reduced (gains electron)
Fig. 9-UN1
becomes oxidized
(loses electron)
becomes reduced
(gains electron)

9. An example is the reaction between methane and O2
The reactant that gives away electrons is called the reducing agent (because it reduces the charge of whatever it gives the electrons to)
The electron receptor is called the oxidizing agent (it increases the charge of whatever it gives electrons to)
Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds
An example is the reaction between methane and O2
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10. Fig. 9-3
A molecule can also be considered oxidized or reduced when its electrons move closer to or farther away from the central atom.
Reactants
Products
becomes oxidized
becomes reduced
Figure 9.3 Methane combustion as an energy-yielding redox reaction
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Water

11. Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced:
becomes oxidized
becomes reduced
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12. Transferring electrons can release energy
Fig. 2-8
Transferring electrons can release energy
Third shell (highest energy
level)
Second shell (higher
energy level)
Energy
absorbed
First shell (lowest energy
level)
Energy
lost
Atomic
nucleus
(b)
When an electron moves to a more electronegative atom, it is held closer to the nucleus of that atom, so it loses potential energy.

13. 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 (like sugars) are usually first transferred to NAD+, an electron carrier
When 2 electrons and 2 H+ are added to NAD+, it becomes NADH (H+ always travels with the electrons)
NAD+ + 2e- + H+  NADH
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14. NADH passes the electrons to the electron transport chain where their energy is harvested
The electron transport chain passes electrons in a series of small steps instead of one explosive reaction
The energy yielded is used to power the endergonic reaction ADP + Pi  ATP
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15. The Stages of Cellular Respiration: A Preview
Cellular respiration has three stages:
Glycolysis (breaks down glucose into two molecules of pyruvate)
In between step: Conversion of Pyruvate into Acetyl CoA
The citric acid cycle (completes the breakdown of glucose)
Oxidative phosphorylation (accounts for most of the ATP synthesis)
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16. Electrons carried via NADH ATP Substrate-level phosphorylation
Fig
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
Cytosol
Figure 9.6 An overview of cellular respiration
ATP
Substrate-level
phosphorylation

17. Electrons carried via NADH Electrons carried via NADH and FADH2
Fig
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

18. Electrons carried via NADH Electrons carried via NADH and FADH2
Fig
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

19. BioFlix: Cellular Respiration
The process that generates most (~ 90%) of the ATP is called oxidative phosphorylation because it is powered by redox reactions
Oxidative = things are being oxidized
Phosphorylation = Phosphate groups are being added to ADP to make ATP
BioFlix: Cellular Respiration
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20. 1st stage: 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 two major phases:
Energy investment phase
Energy payoff phase
Glucose + 2ATP + 2 NAD+  2 Pyruvate+ 4 ATP + 2NADH
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21. Energy investment phase
Fig. 9-8
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+

22. Glucose ATP 1 Hexokinase ADP Glucose-6-phosphate Fig. 9-9-1
Figure 9.9 A closer look at glycolysis
Glucose-6-phosphate

23. Glucose-6-phosphate 2 Phosphogluco- isomerase Fructose-6-phosphate
Fig
Glucose
ATP 1
Hexokinase
ADP
Glucose-6-phosphate
Glucose-6-phosphate 2
Phosphoglucoisomerase 2
Phosphogluco-
isomerase
Fructose-6-phosphate
Figure 9.9 A closer look at glycolysis
Fructose-6-phosphate

24. Fructose- 1, 6-bisphosphate
Fig
Glucose
ATP 1 1
Hexokinase
ADP
Fructose-6-phosphate
Glucose-6-phosphate 2 2
Phosphoglucoisomerase
ATP 3
Phosphofructo-
kinase
Fructose-6-phosphate
ATP 3 3
ADP
Phosphofructokinase
ADP
Figure 9.9 A closer look at glycolysis
Fructose-
1, 6-bisphosphate
Fructose-
1, 6-bisphosphate

25. Aldolase Isomerase Fructose- 1, 6-bisphosphate 4 5 Dihydroxyacetone
Fig
Glucose
ATP 1
Hexokinase
ADP
Glucose-6-phosphate 2
Phosphoglucoisomerase
Fructose-
1, 6-bisphosphate 4
Fructose-6-phosphate
Aldolase
ATP 3
Phosphofructokinase
ADP
Figure 9.9 A closer look at glycolysis 5
Isomerase
Fructose-
1, 6-bisphosphate 4
Aldolase 5
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate

26. Glyceraldehyde- 3-phosphate
Fig
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2 2
1, 3-Bisphosphoglycerate
Glyceraldehyde-
3-phosphate
2 NAD+ 6
Triose phosphate
dehydrogenase 2 P 2
NADH i
+ 2 H+
Figure 9.9 A closer look at glycolysis 2
1, 3-Bisphosphoglycerate

27. 2 2 ADP 2 ATP 2 3-Phosphoglycerate 1, 3-Bisphosphoglycerate 7
Fig
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2
1, 3-Bisphosphoglycerate
2 ADP 7
Phosphoglycerokinase
2 ATP 2
1, 3-Bisphosphoglycerate
2 ADP 2
3-Phosphoglycerate 7
Phosphoglycero-
kinase
2 ATP
Figure 9.9 A closer look at glycolysis 2
3-Phosphoglycerate

28. 2 3-Phosphoglycerate 8 Phosphoglycero- mutase 2 2-Phosphoglycerate
Fig
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2
1, 3-Bisphosphoglycerate
2 ADP 7
Phosphoglycerokinase
2 ATP 2
3-Phosphoglycerate 2
3-Phosphoglycerate 8
Phosphoglyceromutase 8
Phosphoglycero-
mutase 2
2-Phosphoglycerate
Figure 9.9 A closer look at glycolysis 2
2-Phosphoglycerate

29. 2 2-Phosphoglycerate Enolase 2 H2O 2 Phosphoenolpyruvate 9 Fig. 9-9-8
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2
1, 3-Bisphosphoglycerate
2 ADP 7
Phosphoglycerokinase
2 ATP 2
2-Phosphoglycerate 2
3-Phosphoglycerate 8
Phosphoglyceromutase 9
Enolase
2 H2O 2
2-Phosphoglycerate 9
Figure 9.9 A closer look at glycolysis
Enolase
2 H2O 2
Phosphoenolpyruvate 2
Phosphoenolpyruvate

30. 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 Pyruvate
Fig
2 NAD+ 6
Triose phosphate
dehydrogenase 2
NADH 2 P i
+ 2 H+ 2
1, 3-Bisphosphoglycerate
2 ADP 7
Phosphoglycerokinase
2 ATP 2
Phosphoenolpyruvate
2 ADP 2
3-Phosphoglycerate 8 10
Phosphoglyceromutase
Pyruvate kinase
2 ATP 2
2-Phosphoglycerate 9
Figure 9.9 A closer look at glycolysis
Enolase
2 H2O 2
Phosphoenolpyruvate
2 ADP 10
Pyruvate kinase
2 ATP 2
Pyruvate 2
Pyruvate

31. In between step: pyruvate is converted into Acetyl-CoA.
If O2 is present, pyruvate enters the mitochondrion
Before the citric acid cycle (also called the Kreb’s cycle) can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis
In- between step turning pyruvate into Acetyl-CoA:
2 Pyruvate + 2NAD+  2 Acetyl Co-A + 2 NADH + 2Co2
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32. CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 3 Acetyl CoA Pyruvate
Fig. 9-10
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

33. Remember the parts of the mitochondrion?

34. 2 Acetyl CoA  2ATP + 6NADH + 2FADH2 + 4CO2
The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix
Each time you add an Acetyl CoA, the cycle turns once, generating 1 ATP, 3 NADH, and 1 FADH2 per turn
Since each glucose molecule generates 2 pyruvates, and thus 2 Acetyl CoAs, the cycle turns twice for each glucose molecule.
2 Acetyl CoA  2ATP + 6NADH + 2FADH2 + 4CO2
FADH2 is an electron carrier that can hold 2 electrons, very similar to NADH. When it’s not holding electrons, it is called FAD (like NAD+)
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35. Pyruvate CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle 2
Fig. 9-11
Pyruvate
CO2
NAD+
CoA
NADH
+ H+
Acetyl CoA
CoA
CoA
Citric
acid
cycle 2
CO2
Figure 9.11 An overview of the citric acid cycle
FADH2
3 NAD+
FAD 3
NADH
+ 3 H+
ADP + P i
ATP

36. The citric acid cycle has 8 steps, each catalyzed by a specific enzyme
The acetyl part of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate (the CoA part is removed)
The next seven steps change the citrate back to oxaloacetate, making the process a cycle
The carbons that originally came from glucose are turned into CO2 during the cycle
NADH and FADH2 carry electrons to the last stage
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37. Citric acid cycle Succinyl CoA
Fig
Acetyl CoA
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
Figure 9.12 A closer look at the citric acid cycle
-Keto-
glutarate 4 6
CoA—SH
FADH2 5
CO2
NAD+
FAD
Succinate P
NADH i
GTP
GDP
Succinyl
CoA
+ H+
ADP
ATP

38. During oxidative phosphorylation, electron transport creates an H+ concentration gradient, which generates ATP
Most of the energy from glucose is still stored inside the electrons that are being carried by NADH and FADH2
These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis in the oxidative phosphorylation stage of cellular respiration
For the Cell Biology Video ATP Synthase 3D Structure — Side View, go to Animation and Video Files.
For the Cell Biology Video ATP Synthase 3D Structure — Top View, go to Animation and Video Files.
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39. The Pathway of Electron Transport
The electron transport chain is in the cristae of the mitochondrion
Most of the chain’s components are proteins
Each protein is more electronegative than the last
Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O
Image from:
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40. Figure 9.13 Free-energy change during electron transport
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 e– 10 2
(from NADH
or FADH2)
2 H+ + 1/2 O2
H2O

41. The electron transport chain itself generates no ATP
Electrons are transferred from NADH or FADH2 to the electron transport chain
Electrons are passed through a number of proteins and finally to O2 (which came from breathing)
The electron transport chain itself generates no ATP
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 that can be used to do work
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42. The Energy-Coupling Mechanism
Electron transfer in the electron transport chain releases energy, causing proteins to pump H+ from the mitochondrial matrix to the intermembrane space by active transport
H+ then moves back across the membrane, passing through channels in ATP synthase
ATP synthase is like a turbine. The energy released by H+ as it flows through the synthase is added onto ADP and Pi to allow them to form ATP.
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43. INTERMEMBRANE SPACE H+ ADP + P ATP MITOCHONDRIAL MATRIX i Fig. 9-14
Figure 9.14 ATP synthase, a molecular mill
ADP + P
ATP i
MITOCHONDRIAL MATRIX

44. Each NADH makes about 2.5 ATP
As the H+ ions go down their concentration gradient through the ATP synthase, ATP synthase turns and phosphorylates ADP, making ATP.
Each NADH makes about 2.5 ATP
Each FADH2 makes about 1.5 ATP, because FADH2 donates its electrons in the middle of the electron transport chain, not at the beginning, so not as many H+ are pumped across the membrane for each FADH2
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45. Electron transport chain 2 Chemiosmosis
Fig. 9-16 H+ H+ H+ H+
Protein complex
of electron
carriers
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

46. An Accounting of ATP Production by Cellular Respiration
During cellular respiration, most energy flows with the electrons, which move in this order:
glucose  NADH  electron transport chain  H+ gradient force  ATP
About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32 ATP
What happens to the rest of the energy from glucose?
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47. Fig. 9-17
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 26 or 28 ATP
Figure 9.17 ATP yield per molecule of glucose at each stage of cellular respiration
About
30 or 32 ATP
Maximum per glucose:

48. Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen
Most cellular respiration requires O2 to produce ATP
Glycolysis can produce its 2 ATP with or without O2 (in aerobic or anaerobic conditions)
In the absence of O2, glycolysis is used to make ATP, followed by fermentation or anaerobic respiration
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49. Anaerobic respiration uses an electron transport chain with an electron acceptor other than O2, for example sulfate
Mostly used by bacteria that live in oxygen-free environments
Fermentation uses glycolysis, but not the citric acid cycle or electron transport chain, to make ATP
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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 and lactic acid fermentation
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51. Pyruvate + NADH  Alcohol + CO2 + NAD+
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
Pyruvate + NADH  Alcohol + CO2 + NAD+
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52. (a) Alcohol fermentation
Fig. 9-18a
2 ADP + 2 P
2 ATP i
Glucose
Glycolysis
2 Pyruvate
2 NAD+
2 NADH 2
CO2
+ 2 H+
Figure 9.18a Fermentation
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation

53. Pyruvate + NADH  Lactate + NAD+
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
Pyruvate + NADH  Lactate + NAD+
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54. (b) Lactic acid fermentation
Fig. 9-18b
2 ADP + 2 P
2 ATP i
Glucose
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 Pyruvate
Figure 9.18b Fermentation
2 Lactate
(b) Lactic acid fermentation

55. Why do fermentation? Why not just keep making ATP through glycolysis?
Without oxygen, pyruvate builds up and all the NAD+ carriers get full of electrons.
Eventually glycolysis will stop!
Fermentation regenerates the NAD+ carriers so glycolysis can continue.
NAD+

56. Fermentation and Aerobic Respiration Compared
Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate
Aerobic respiration uses O2; fermentation doesn’t.
Aerobic respiration produces ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule
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57. Ethanol or lactate Citric acid cycle
Fig. 9-19
Glucose
Glycolysis
CYTOSOL
Pyruvate
O2 present:
Aerobic cellular
respiration
No O2 present:
Fermentation
MITOCHONDRION
Ethanol or
lactate
Acetyl CoA
Figure 9.19 Pyruvate as a key juncture in catabolism
Citric
acid
cycle

58. Glucose is not the only fuel for respiration
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration, including carbohydrates, fats, and proteins
These molecules may be partially broken down before entering glycolysis or the citric acid cycle
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59. Citric acid cycle Oxidative phosphorylation
Fig. 9-20
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Figure 9.20 The catabolism of various molecules from food
Citric
acid
cycle
Oxidative
phosphorylation

60. CARBOHYDRATES SUPPLY ENERGY
Remember ! Why do we need carbohydrates?
CARBOHYDRATES SUPPLY ENERGY
Cells burn GLUCOSE
for their energy needs (easier than burning fats or proteins)
Images from:

61. EXERCISE and ENERGY (Short term energy) Cells normally contain small
EXERCISE and ENERGY
(Short term energy)
Cells normally contain small
amounts of ATP produced by
glycolysis &
cellular respiration (only enough for a few seconds of activity)
Once this ATP is used up, lactic acid
fermentation can provide enough ATP
to last about 90 seconds of intense exercise.

62. EXERCISE and ENERGY (Short term energy)
Once the race is over, lactic acid
must be broken down using oxygen.
A quick sprint builds up an
oxygen debt that
must be repaid by
heavy breathing.
Image from:

63. EXERCISE and ENERGY
(LONGER term energy)
For exercise longer than 90 seconds
Aerobic respiration is the only
way to make enough ATP.
Cellular respiration releases energy
more slowly than fermentation and requires plenty of oxygen.
Well conditioned athletes must pace themselves during a long race.

64. What happens in a long race when the body’s glucose is all used up?
Animal cells store
glucose as
glycogen
to use later.
Image from:

65. EXERCISE and ENERGY
(LONGER term energy)
Muscle cells store glycogen which can be broken down into glucose to supply energy for minutes
of activity.

66. EXERCISE and ENERGY (LONGER term energy)
After glycogen stores are used up the body breaks down fat. That’s why aerobic exercise must continue for longer than 20 minutes if you want to
lose fat!

67. ALL CELLS NEED ENERGY All eukaryotes (including plant and animal cells) have mitochondria for cellular respiration
All prokaryotes (bacteria and archaea)
have their electron transport enzymes
attached to their
cell membranes

68. How do cells control how much ATP is produced?
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 cellular respiration is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway
ATP can act as an inhibitor for these enzymes
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69. Figure 9.21 The control of cellular respiration
Glucose
AMP
Glycolysis
Fructose-6-phosphate
Stimulates +
Phosphofructokinase – –
Fructose-1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Figure 9.21 The control of cellular respiration
Citric
acid
cycle
Oxidative
phosphorylation