1. Cellular Respiration: Harvesting Chemical Energy
BioA-Ch9-106
Cellular Respiration: Harvesting Chemical Energy
生物及解剖學科
藍心婕
18705

2. 9.0 Overview: Life Is Work
Living cells require transfusions of energy from outside sources to perform their many tasks
Some animals, such as the giraffe, obtain energy by eating plants, and some animals feed on other organisms that eat plants

3. Energy flows into an ecosystem as sunlight and leaves as heat

4. Muscle cells carrying out
Breathing O2
CO2
Lungs
CO2 O2
Bloodstream
Figure 6.2 The connection between breathing and cellular respiration.
Muscle cells carrying out
Cellular Respiration
Glucose + O2
CO2 + H2O + ATP

5. Catabolic pathways and production of ATP
9.1: Catabolic pathways異化作用yield energy by oxidizing organic fuels
Catabolic pathways and production of ATP
The breakdown of organic molecules is exergonic釋能的.
Catabolic process:
Fermentation發酵作用(anaerobic respiration): a partial degradation of sugars that occurs without oxygen.
Cellular respiration呼吸作用(aerobic respiration): consumes oxygen and organic molecules such as glucose to yields ATP
C6H12O6 ＋ 6O2  6CO2 ＋ H2O ＋ energy (ATP ＋ heat)
Free energy (ΔG)= kcal /mol

6. To keep working cells must regenerate ATP
ATP transfers phosphate groups to various substrates, priming them to do work.

7. B. Redox氧化還原反應reactions: reduction and oxidation
Catabolic pathways yield energy due to the transfer of electrons
The principle of redox
Redox reactions: transfer electrons from one reactant to another by oxidation and reduction.
Oxidation氧化: substance loses electrons, or is oxidized.
Reduction還原: substance gains electrons, or is reduced.
oxidation oxidation
Na ＋ Cl  Na＋ ＋ Cl－ Xe－ ＋ Y  X ＋ Ye－
reduction reduction
Some redox reactions do not completely exchange electrons but change the degree of electron sharing in covalent bonds

8. becomes oxidized becomes reduced
Reactants
Products
Methane
(reducing
agent)
Oxygen
(oxidizing
Carbon dioxide
Water
becomes oxidized
becomes reduced
becomes oxidized
becomes reduced

9. Oxidation of organic fuel molecules during cellular respiration
During cellular respiration, glucose is oxidized and oxygen is reduced
Stepwise energy harvest via NAD+ and the electron transport chain
Cellular respiration oxidizes glucose in a series of steps
Electrons from organic compounds are usually first transferred to NAD+, than passes the electrons to the electron transport chain電子傳遞鏈.
NAD+: a coenzyme輔酶; NADH: the reduced form of NAD+
NAD+
2 e− + 2 H+
2[H]
(from food)
Nicotinamide
(oxidized form)
Reduction of NAD+
2 e− + H+
NADH
(reduced form)
Oxidation of NADH H+
Dehydrogenase

10. If electron transfer is not stepwise, a large release of energy occurs as in the reaction of hydrogen and oxygen to form water.
Electron transport chain: passes electrons in a series of steps and uses the energy from the electron transfer to form ATP. H2 +
½ O2
2 H
2 H+
2 e−
H2O
Controlled
release of
energy
Electron transport
chain
ATP
Explosive
release
Cellular respiration
Uncontrolled reaction
(a)
(b)
Free energy, G

11. The Stages of Cellular Respiration: A Preview
Respiration has three metabolic stages: glycolysis醣解作用, citric acid cycle 檸檬酸循環 and oxidative phosphorylation氧化磷酸化
Glycolysis (Glyco = sweet, sugar; lysis = to split): breaks down glucose into two molecules of pyruvate丙酮酸
Electrons
via NADH
GLYCOLYSIS
Glucose
Pyruvate
CYTOSOL
MITOCHONDRION
ATP
Substrate-level

12. Citric acid cycle: completes the breakdown of glucose
Oxidative phosphorylation: driven by the electron transport chain and generates ATP.
Electrons
via NADH
and FADH2
ATP
CYTOSOL
MITOCHONDRION
Substrate-level
Oxidative
GLYCOLYSIS
PYRUVATE
OXIDATION
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron transport
and chemiosmosis)
Acetyl CoA
Glucose
Pyruvate

13. Two mechanisms of ATP generation
Cells use the energy released by “falling” electrons to pump H+ ions across a membrane
The energy of the gradient is harnessed to make ATP by the process of chemiosmosis
High H+ concentration
ATP synthase uses gradient energy to make ATP
Membrane
Electron transport chain
ATP synthase
Energy from
Low H+ concentration
Figure 6.7A

14. substrate-level phosphorylation 受質階層磷酸化
Both glycolysis and the citric acid cycle can generate ATP by
substrate-level phosphorylation 受質階層磷酸化
Enzyme
Substrate
Product
ATP
ADP P

15. Energy Investment Phase
9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate
Energy Investment Phase
Glycolysis: splitting of sugar, breaks down glucose into pyruvate, occurs in the cytoplasm of the cell.
Glycolysis consists of two major phases:
energy investment phase
耗能階段;
energy payoff phase
產能階段
Glucose 2
ATP
used
2 ADP + 2 P
Energy Payoff Phase 4
ADP + 4 P 4
ATP
formed 2
NAD+ +
4 e− +
4 H+ 2
NADH +
2 H+ 2
Pyruvate + 2
H2O
Net
Glucose 2
Pyruvate + 2
H2O 4
ATP formed − 2
ATP used 2
ATP 2
2 NAD+ + 4 e− + 4 H+ 2
NADH + 2 H+

16. 1 2 Glucose Fructose ATP 6-phosphate ADP
Figure 9.9a
GLYCOLYSIS: Energy Investment Phase
Glucose
6-phosphate
ATP
ADP
Hexokinase
Phosphogluco-
isomerase
Fructose 1 2
Figure 9.9 A closer look at glycolysis.
Figure 9.9 A closer look at glycolysis.

17. 5 4 3 Glyceraldehyde 3-phosphate (G3P) ATP Fructose 6-phosphate
Figure 9.9b
GLYCOLYSIS: Energy Investment Phase 3 4 5
Fructose
6-phosphate
ATP
ADP
Glyceraldehyde
3-phosphate (G3P)
1,6-bisphosphate
Dihydroxyacetone
phosphate (DHAP)
Phospho-
fructokinase
Aldolase
Isomerase
Figure 9.9 A closer look at glycolysis.

18. 4 5 6 7 GLYCOLYSIS: Energy Payoff Phase Glyceraldehyde
Figure 9.9c
GLYCOLYSIS: Energy Payoff Phase 4
Glyceraldehyde
3-phosphate (G3P)
Dihydroxyacetone
phosphate (DHAP)
Aldolase
Isomerase 5 6 7
Triose
phosphate
dehydrogenase
2 NAD+
2 H+
NADH 2
2 ADP
1,3-Bisphospho-
glycerate
3-Phospho-
Phospho-
glycerokinase
ATP
Figure 9.9 A closer look at glycolysis.

19. 8 9 10 GLYCOLYSIS: Energy Payoff Phase 3-Phospho- glycerate 2-Phospho-
Figure 9.9d 8 9 10
Phospho-
glyceromutase
3-Phospho-
glycerate
2-Phospho- 2
Enolase
Phosphoenol-
pyruvate (PEP)
Pyruvate
kinase
ATP
ADP
H2O
GLYCOLYSIS: Energy Payoff Phase
Figure 9.9 A closer look at glycolysis.

20. Transport protein NAD+ H+ NADH +
9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules
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 multienzyme complex that catalyses three reactions
CYTOSOL
Pyruvate
Transport protein
MITOCHONDRION
Acetyl CoA
NAD+ H+
NADH +
CO2
Coenzyme A 1 2 3

22. An overview of the citric acid cycle
PYRUVATE OXIDATION
Pyruvate (from glycolysis,
2 molecules per glucose)
NADH
NAD+
CO2
CoA
+ H+
CITRIC
ACID
CYCLE
FADH2
FAD
ATP
ADP + P i
3 H+ 3 2
Acetyl CoA
An overview of 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

23. CITRIC OXIDATIVE PYRUVATE ACID PHOSPHORYL- GLYCOLYSIS OXIDATION CYCLE
Figure 9.UN08
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYL-
ATION
PYRUVATE
OXIDATION
GLYCOLYSIS
Figure 9.UN08 In-text figure, mini-map, citric acid cycle, p. 171
ATP
ATP

24. CITRIC ACID CYCLE Acetyl CoA Oxaloacetate Citrate -Ketoglutarate
H2O
+ H+
Oxaloacetate
CoA-SH
Citrate
-Ketoglutarate
NAD+
CO2
NADH
Succinyl
CoA
ATP
ADP
GTP
GDP
Succinate
FAD
FADH2
Fumarate
Malate
CITRIC
ACID
CYCLE P i
Isocitrate 1 2 5 6 4 3 7 8

25. 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(OAA), 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

26. 1 2 H2O Acetyl CoA Oxaloacetate Citrate Isocitrate CoA-SH Figure 9.12a
Figure 9.12 A closer look at the citric acid cycle.

27. 3 4 Isocitrate -Ketoglutarate Succinyl CoA CO2 NAD+ NADH + H+
Figure 9.12b 3 4
-Ketoglutarate
CO2
NAD+
NADH
+ H+
CoA-SH
Isocitrate
Succinyl
CoA
Figure 9.12 A closer look at the citric acid cycle.

28. 6 5 FADH2 FAD GTP GDP ADP ATP P Fumarate Succinate Succinyl CoA CoA-SH
Figure 9.12c
Succinyl
CoA 6 5
Fumarate
FADH2
FAD
Succinate
GTP
GDP
ADP
ATP P i
CoA-SH
Figure 9.12 A closer look at the citric acid cycle.

29. 8 7 NADH H2O + H+ NAD+ Oxaloacetate Malate Fumarate Figure 9.12d
Figure 9.12 A closer look at the citric acid cycle.

30. CITRIC ACID CYCLE Acetyl CoA Oxaloacetate Citrate -Ketoglutarate
H2O
+ H+
Oxaloacetate
CoA-SH
Citrate
-Ketoglutarate
NAD+
CO2
NADH
Succinyl
CoA
ATP
ADP
GTP
GDP
Succinate
FAD
FADH2
Fumarate
Malate
CITRIC
ACID
CYCLE P i
Isocitrate 1 2 5 6 4 3 7 8

32. 1953年英國醫博士 Sir Hans Krebs 發表了一篇“the citric acid cycle”簡稱TCA cycle ( 檸檬酸周期循環 )榮獲諾貝爾獎，於次年受聘為牛津大學生化系主任，並受英國皇室冊封為爵士 以表彰其對人類生化研究上之偉大貢獻。
Professor Sir Hans Krebs FRS, , biochemist, Nobel laureate

33. 青蒿素(Artemisinin)
阿維菌素（Avermectins)
大村智
屠呦呦

34. 東京工業大學教授大隅良典 （Yoshinori Ohsumi）
細胞自噬作用（Autophagy）

35. GLYCOLYSIS
CITRIC
ACID
CYCLE
PYRUVATE
OXIDATION
ATP
OXIDATIVE
PHOSPHORYL-
ATION
9.4: During oxidative phosphorylation, chemiosmosis couples electron transport
to ATP synthesis
NADH and FADH2: donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation
The Pathway of Electron Transport
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
Multiproteins including cytochromes (each with an iron atom)

36. Chemiosmosis: The Energy-Coupling Mechanism 能量偶合機制
The electron transport chain generates no ATP directly
Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space
H+ then moves back across the membrane, passing through the protein complex, ATP synthase
ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP

37. ATP Synthase 3-D Structure
Top View
Side View

38. The H+ gradient is referred to as a proton-motive force 質子驅動力, emphasizing its capacity to do work
Protein
complex
of electron
carriers
(carrying
electrons
from
food)
ATP
synthase
Electron transport chain
Chemiosmosis
Oxidative phosphorylation
2 H+ + ½ O2
H2O
ADP + P i H+
Cyt c Q I II
III IV
FAD
FADH2
NADH
NAD+ 1 2

39. 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

40. Electron shuttles span membrane CYTOSOL MITOCHONDRION 2 NADH or
Figure 9.16
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
GLYCOLYSIS
PYRUVATE
OXIDATION
2 Acetyl CoA
OXIDATIVE
PHOSPHORYLATION
(Electron transport
and chemiosmosis)
CITRIC
ACID
CYCLE
Glucose 2
Pyruvate
+ 2 ATP
+ 2 ATP
+ about 26 or 28 ATP
Figure 9.16 ATP yield per molecule of glucose at each stage of cellular respiration
About
30 or 32 ATP
Maximum per glucose:

41. Cellular respiration relies on oxygen to produce ATP
9.5 Fermentation and anaerobic respiration enables some cells to produce ATP without the use of oxygen
Cellular respiration relies on oxygen to produce ATP
In the absence of oxygen cells can still produce ATP through fermentation
Glycolysis can produce ATP with or without oxygen, in aerobic or anaerobic conditions, and couples with fermentation to produce ATP
glucose
glycolysis
no O O2
pyruvate
reduced to ethanol or lactate oxidized to acetyl CoA
& &
NAD＋is recycled as NADH is oxidize oxidation continues in Krebs cycle

42. Types of Fermentation
Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysis
Alcohol 酒精fermentation: pyruvate is converted to ethanol in two steps, one of which releases CO2.
Lactic acid 乳酸fermentation: pyruvate is reduced directly to NADH to form lactate as a waste product
2 ADP + 2 P i 2
ATP
Glucose
NAD+
NADH
+ 2 H+
2 Pyruvate
CO2
2 Ethanol
(a)
Alcohol fermentation
2 Acetaldehyde
2 Lactate
Lactic acid fermentation
GLYCOLYSIS
Pyruvate
(b)

43. Fermentation and Cellular Respiration Compared
Both fermentation and cellular respiration use glycolysis to oxidize glucose and other organic fuels to pyruvate
Fermentation and cellular respiration differ in their final electron acceptor
Cellular respiration produces more ATP
Pyruvate is a key juncture in catabolism
Glucose
Glycolysis
CYTOSOL
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
Ethanol,
lactate, or
other products
MITOCHONDRION
Acetyl CoA
CITRIC
ACID
CYCLE
The Evolutionary Significance of Glycolysis
Glycolysis occurs in nearly all organisms, probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

44. The Versatility of Catabolism多功能的異化作用
9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways
The Versatility of Catabolism多功能的異化作用
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration
The catabolism of various molecules from food
Biosynthesis (Anabolic Pathways同化作用)
The body uses small molecules to build other substances
These small molecules may come directly from food or through glycolysis or the citric acid cycle
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
GLYCOLYSIS
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Acetyl CoA
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION

45. ATP needed to drive biosynthesis Cells, tissues, organisms
Biosynthesis of macromolecules from intermediates in cellular respiration
ATP needed to drive biosynthesis
GLUCOSE SYNTHESIS
Citric acid cycle
Acetyl CoA
pyruvate
G3P
Glucose
Amino groups
Amino acids
Fatty acids
Glycerol
Sugars
Proteins
Fats
Polyscaccharides
Cells, tissues, organisms
Figure 6.17

46. Regulation 調節of Cellular Respiration via Feedback回饋Mechanisms

47. The control of cellular respiration:
phosphofructokinase is allosteric enzyme, citrate and ATP are
allosteric inhibitors抑制物of phosphofructokinase,
ADP and AMP are allosteric activators活化物 for phosphofructokinase
Glucose
AMP
Stimulates
GLYCOLYSIS
Fructose 6-phosphate
Phosphofructokinase
Fructose 1,6-bisphosphate
Inhibits
Citrate
Pyruvate
Acetyl CoA
ATP
CITRIC
ACID
CYCLE
Oxidative
phosphorylation

48. You should now be able to:
Explain in general terms how redox reactions are involved in energy exchanges.
Name the three stages of cellular respiration; for each, state the region of the eukaryotic cell where it occurs and the products that result
In general terms, explain the role of the electron transport chain in cellular respiration
Explain where and how the respiratory electron transport chain creates a proton gradient
Distinguish between fermentation and anaerobic respiration
Distinguish between obligate and facultative anaerobes