Download Document

Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
高醫 生物醫學暨環境生物學系
助理教授 張學偉
http://genomed.dlearn.kmu.edu.tw
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Energy
– Flows into an ecosystem as sunlight and
leaves as heat
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Heat
energy
• To keep working, cells must regenerate ATP
本圖補充
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Figure 9.6
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Substrate-level
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
Concept
1: Catabolic pathways yield energy by oxidizing organic fuels
2: Glycolysis harvests energy by oxidizing glucose to
pyruvate
3: The citric acid cycle completes the energy-yielding
oxidation of organic molecules
4: During oxidative phosphorylation, chemiosmosis couples
electron transport to ATP synthesis
5: Fermentation enables some cells to produce ATP without
the use of oxygen
6: Glycolysis and the citric acid cycle connect to many other
metabolic pathways
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.1: Catabolic pathways yield energy
by oxidizing organic fuels
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Catabolic Pathways and Production of ATP
Catabolic pathways (異化)
yield energy by oxidizing
organic fuels
同化作用
本圖為補充
exergonic (產能的)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
endergonic 耗能的
• One catabolic process, fermentation (發酵)
– Is a partial degradation of sugars that occurs
without oxygen
稍後再講
Conecept 5: Fermentation enables some cells to
produce ATP without the use of oxygen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cellular respiration
– Is the most prevalent and efficient catabolic
pathway
– Consumes oxygen (with O2 as the ultimate
electron acceptor) and organic molecules such
as glucose
– Yields ATP
It is called cellular respiration to distinguish it from the
respiration of breathing.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Redox Reactions: Oxidation and Reduction
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Definition of Oxidation & Reduction and its agent
• In oxidation
– A substance loses electrons, or is oxidized
Reducting Agent
• In reduction
– A substance gains electrons, or is reduced
Oxidating Agent
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
becomes reduced
(gains electron)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cl–
• Some redox reactions
– Do not completely exchange electrons
– Change the degree of electron sharing in covalent
bonds 注意 : blue ball位置
Products
Reactants
becomes oxidized
+
CH4
2O2
2 H2O
O
O
C
O
H
O
H
H
H
O
注意 : blue ball位置
H
Methane
(reducing
agent)
+
Energy
becomes reduced
H
C
+
CO2
Oxygen
(oxidizing
agent)
Figure 9.3
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Carbon dioxide
Water
Oxidation of Organic Fuel Molecules During
Cellular Respiration
•
During cellular respiration:
- Glucose is oxidized in a series of steps and oxygen is reduced
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy △G = - 686 Kcal
becomes reduced
△G < 0
1. spontaneous reaction (without an input of energy)
2. Liberating energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
NAD+ = Nicotinamide adenine dinucleotide
2 e– + 2 H+
NAD+
H
O
O–
O
O P
O
H
–
O P O HO
NH2
O
N+ Nicotinamide
(oxidized form)
H
OH
HO
CH2
O
H
HO
H
OH
N
H
H
+ 2[H]
• Nucleosides = Sugar
(from food) Oxidation of NADH
phosphate)
N
H
N
Reduction of NAD+
NH2
N
H+
NADH
• Nucleotide
= Base + Sugar
Dehydrogenase
O + Phosphate
O
C
CH2
2 e– + H+
adenine
Figure 9.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
H
C NH2
+ Base
(no
N
Nicotinamide
(reduced form)
+
H+
• Electrons from organic compounds
– Are usually first transferred to NAD+, a coenzyme
electron
2
e– +
proton
2 H+
NAD+
Dehydrogenase
O
NH2
H
C
CH2
O
O–
O
O P
O
H
–
O P O HO
O
N+ Nicotinamide
(oxidized form)
H
OH
HO
CH2
N
H
H
HO
N
H
OH
Reduction of NAD+
+ 2[H]
(from food) Oxidation of NADH
Hydrogen
atom
H O
C
H
N
H+
NADH
NH2
+
H+
Nicotinamide
(reduced form)
NH2
N
O
2 e– + H+
N
H
2H
NAD+ + H+ +2e= NAD+ + 2H
Figure 9.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
 2H+ +2e- (oxidation)
 NADH (reduction)
 NADH + H+
Ex. A
 B + 2H+ +2e- (oxidation)
(+) FAD + 2H+ +2e-  FADH2
(reduction)
=
A+ FAD <=> B+ FADH2
A+ FAD <=> B+ FADH2
A+ NAD(P) <=> B+ NAD(P)H
A is the electron donor (so it is oxidized)
FAD & NAD(P) is the electron acceptor (so it is reduced).
The products of the reaction are B (oxidized state)
FADH2 or NAD(P)H (reduced state) .
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
圖形為補充
• NADH passes the electrons to the electron transport chain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• If electron transfer is not stepwise
– A large release of energy occurs
– As in the reaction of hydrogen and oxygen to
form water
Free energy, G
H2 + 1/2 O2
Figure 9.5 A
Explosive
release of
heat and light
energy
H2O
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(a) Uncontrolled reaction
比較 The electron transport chain
2H
• Passes electrons in a
series of steps instead of
in one explosive reaction
2
O2
1/
O2
(from food via NADH)
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
Free energy, G
• Uses the energy from the
electron transfer to form
ATP
1/
+
ATP
ATP
ATP
2 e–
2
H+
H2O
Figure 9.5 B
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(b) Cellular respiration
2
• An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
1
2
Glycolsis
Pyruvate
Glucose
Cytosol
Oxidative
3phosphorylation:
electron
transport and
chemiosmosis
Mitochondrion
ATP
Figure 9.6
Citric
acid
cycle
Substrate-level
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
• Glycolysis
– Breaks down glucose into two molecules of
pyruvate
• The citric acid cycle
– Completes the breakdown of glucose
• Oxidative phosphorylation
– Is driven by the electron transport chain
– Generates ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
substrate-level phosphorylation
• generate ATP from glycolysis and TCA cycle
Enzyme
Enzyme
ADP
P
Substrate
Figure 9.7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
+
Product
ATP
• Concept 9.2: Glycolysis harvests energy by
oxidizing glucose to pyruvate
• Glycolysis
– Means “splitting of sugar”
– Breaks down glucose into pyruvate
– Occurs in the cytoplasm of the cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glycolysis
ATP
Citric
acid
cycle
Oxidative
phosphorylation
ATP
ATP
Energy investment phase
• Glycolysis consists of
two major phases
Glucose
2 ATP + 2
– Energy investment
phase
used
2 ATP
Energy payoff phase
4 ADP + 4
– Energy payoff
phase
P
4 ATP
P
formed
2 NADH
2 NAD+ + 4 e- + 4 H +
+ 2 H+
2 Pyruvate + 2 H2O
Figure 9.8
Net Rx
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H +
2 Pyruvate + 2 H2O
2 ATP
+ 2 H+
2 NADH
Net Rx: Glucose + 2ADP+ 2Pi + NAD+ 2 Pyruvate + 2ATP + 2NADH + 2 H+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
investment phase
payoff phase
Glycolysis
Citric
acid
cycle
Oxidative
phosphorylation
2
CH2 O P
1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
ADP
2 ATP
H
OH
Glucose-6-phosphate
2
Phosphoglucoisomerase
P
O CH2OH
H HO
OH
H
H
HO
Fructose-6-phosphate
CH2O
3
ATP
O C O
CHOH
1
Hexokinase
CH2O P
HH O H
OH H
OH
HO
2 Pi
2 NADH
+ 2 H+
P
ATP
6
Triose phosphate
dehydrogenase
2 NAD+
CH2OH
OH
HH
OH H
HO
OH
H OH
Glucose
Kinase
isomerase
Mutase
Aldolase
enolase
Dehydrogenase
Phosphofructokinase
ADP
O–
2
C
CHOH
CH2 O P
3-Phosphoglycerate
8
Phosphoglyceromutase
2
O–
C
O
H C O
P
CH2OH
2-Phosphoglycerate
9
Enolase
2H O
2
P
O CH2 O CH2 O
H HO
OH
H
HO
H
Fructose1, 6-bisphosphate
2
P
O–
C O
C O
4
Aldolase
Pyruvate kinase
2 ATP
5
P
O CH2
C O
CH2OH
Dihydroxyacetone
phosphate
Isomerase
H
2
C O
Figure 9.9 A
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
O–
C O
CHOH
CH2 O P
Glyceraldehyde3-phosphate
P
CH2
Phosphoenolpyruvate
2 ADP
10
C O
Figure 9.8
CH3
Pyruvate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.3: The citric acid cycle completes
the energy-yielding oxidation of organic
molecules
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The citric acid cycle
– Takes place in the matrix of the mitochondrion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Before citric acid cycle can begin
– Pyruvate must first be converted to acetyl CoA,
which links the cycle to glycolysis
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
O–
S
CoA
C
O
2
C
O
Pyruvate Oxidation
C
O
1
3
CH3
Pyruvate
Acetyle CoA
CO2
Coenzyme A
From Vit B
Transport protein
Figure 9.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CH3
• An overview of the citric acid cycle
= TCA (Tricarboxyl acid)
Pyruvate
(from glycolysis,
2 molecules per glucose)
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylatio
n
ATP
CO2
CoA
NADH
+ 3 H+ Acetyle CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD+
FADH2
FAD
3 NADH
+ 3 H+
ADP + P i
ATP
Figure 9.11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
= Krebs Cycle
A closer look at the citric acid cycle
Glycolysis
Citric
Oxidative
acid phosphorylation
cycle
S
CoA
C
O
CH3
Acetyl CoA
CoA SH
O
NADH
+ H+
C COO–
COO–
1
CH2
COO–
NAD+
8 Oxaloacetate
HO C
COO–
COO–
CH2
COO–
HO CH
H2O
CH2
CH2
2
HC COO–
COO–
Malate
HO
Citrate
CH2
COO–
Isocitrate
COO–
H2O
CH
7
COO–
CH
CO2
Citric
acid
cycle
3
NAD+
COO–
Fumarate
HC
CH2
CoA SH
6
CoA SH
COO–
FAD
CH2
CH2
COO–
C O
Succinate
4
C O
COO–
CH2
5
CH2
FADH2
COO–
+ H+
a-Ketoglutarate
CH2
COO–
NADH
Pi
S
CoA
GTP GDP Succinyl
NAD+
CO2
NADH
+ H+
CoA
ADP
ATP
Figure 9.12
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
A closer look at the citric acid cycle
Citric
Oxidative
acid phosphorylation
cycle
Glycolysis
2C
3C
pyruvate
S
CoA
C
O
CH3
NAD + CoA
NADH + CO2
Acetyl CoA
4C
O
NADH
+ H+
CoA SH
6C
C COO–
COO–
1
CH2
COO–
NAD+
8 Oxaloacetate
HO C
½ Glucose
4C
COO–
COO–
CH2
COO–
HO CH
H2O
CH2
CH2
2
HC COO–
COO–
Malate
Figure
CH2
HO
Citrate
9.12
Isocitrate
COO–
4C
CH
CO2
Citric
acid
cycle
7
3
NAD+
COO–
Fumarate
HC
CH2
CoA SH
CoA SH
COO–
FAD
CH2
CH2
COO–
C O
Succinate
4C
Pi
S
CoA
GTP GDP Succinyl
CoA
ADP
ATP
Figure 9.12
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4
C O
COO–
CH2
5
CH2
FADH2
COO–
4C
NAD+
NADH
+ H+
NADH
+ H+
a-Ketoglutarate
CH2
COO–
6
6C
COO–
COO–
H2O
CH
CO2
5C
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Energetics
DHase
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.4: During oxidative phosphorylation,
chemiosmosis couples electron transport to
ATP synthesis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Figure 9.6
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Substrate-level
phosphorylation
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
• NADH and FADH2: Donate electrons to the electron
transport chain (ETC), which powers ATP synthesis
via oxidative phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Pathway of Electron Transport
• In the ETC
NADH
50
– Electrons from
NADH and FADH2
lose energy in
several steps
FADH2
Free energy (G) relative to O2 (kcl/mol)
40
• At the end of the chain
Multiprotein
complexes
FAD
Fe•S
Fe•S
II
O
III
Cyt b
30
Fe•S
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
20
10
– Electrons are passed to
oxygen, forming water
0
Figure 9.13
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
I
FMN
2 H + + 12
O2
H2 O
Chemiosmosis: The Energy-Coupling Mechanism
• ATP synthase is the enzyme that actually
makes ATP
INTERMEMBRANE SPACE
H+
rotor
H+
H+
H+
H+
H+
H+
A
within
the
membrane spins
clockwise when
H+ flows past
it down the H+
gradient.
stator
A
anchored
in the membrane
holds the knob
stationary.
注意: H+& ATP的方向
rod
H+
A
(for “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
Three catalytic
sites in the
ADP
+
Pi
Figure 9.14
MITOCHONDRIAL MATRIX
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
knob
ATP
stationary
join inorganic
Phosphate to ADP
to make ATP.
• At certain steps along the electron transport
chain
– Electron transfer causes protein complexes to
pump H+ from the mitochondrial matrix to the
intermembrane space. [逆反應; 與產生ATP時
的H+運送方向相反]
目的: resulting H+ gradient
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The resulting H+ gradient
– Stores energy
– Is referred to as a proton-motive force
– Drives chemiosmosis in ATP synthase
• Chemiosmosis
– Is an energy-coupling mechanism that uses
energy in the form of a H+ gradient across a
membrane to drive cellular work
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chemiosmosis & electron transport chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane
ATP
ATP
H+
H+
H+
Intermembrane
space
Protein complex
of electron
carners
Q
I
IV
III
Inner
mitochondrial
membrane
ATP
synthase
II
FADH2
NADH+
Mitochondrial
matrix
H+
Cyt c
FAD+
NAD+
2 H+ + 1/2 O2
H2O
ADP +
ATP
Pi
(Carrying electrons
from, food)
H+
Chemiosmosis
Electron transport chain
Electron transport and pumping of protons (H+), ATP synthesis powered by the flow
which create an H+ gradient across the membrane Of H+ back across the membrane
Oxidative phosphorylation
Figure 9.15
NADH  3 ATP; FADH2  2 ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
An Accounting of ATP Production by Cellular
Respiration
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
6 NADH
Citric
acid
cycle
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
+ 2 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by substrate-level by oxidative phosphorylation, depending
on which shuttle transports electrons
phosphorylation
from NADH in cytosol
About
36 or 38 ATP
Figure 9.16
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Shuttles for transfer of reducing equivalents
from cytosol into mitochondria
補充 不考
DHAP/GA3P shuttle
Malate/Asp shuttle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glycolysis (aerobic)
Glucose +2ADP + 2Pi+ 2NAD+ 2 pyruvate +2ATP+2NADH+2H++2H2O
aerobic
Pyruvate Oxidation
1 Pyruvate + NAD+ + CoASH  1 Acetyl-CoA + 1 NADH + CO2
2 Pyruvate + 2 NAD+ + 2 CoASH  2 Acetyl-CoA + 2 NADH + 2 CO2
TCA
2 Acetyl-CoA + 4 H2O + 6 NAD+ + 2FAD + 2GDP + 2 Pi  2 CO2 + 6 NADH + 2 FADH2 + 2 CoA-SH + 2 GTP
Glycolysis 
2 ATP
2 NADH (2H)
Pyruvate Oxidation  TCA
2 (2x1) NADH
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2 (2x1) GTP/ATP
6 (2x3) NADH
2 (2x1) FADH2
Glycolysis (aerobic)
Glycolysis 
2 ATP
2 NADH (2H)
Pyruvate Oxidation  TCA
2 (2x1) NADH
2 (2x1) GTP/ATP
6 (2x3) NADH
2 (2x1) FADH2
NADH  3 ATP; FADH2  2 ATP EST & chemiosmosis
ATP 8
or (6) shuttle
6
2 + 18 + 4 = 38
= 36
• About 40% of the energy in a glucose molecule
– Is transferred to ATP during cellular respiration, making
approximately 38 ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.5: Fermentation enables some cells
to produce ATP without the use of oxygen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cellular respiration
– Relies on oxygen to produce ATP
• In the absence of oxygen [no cellular respiration]
– Cells can still produce ATP through
fermentation
• fermentation is a partial degradation of sugars that
occurs without oxygen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Glycolysis
– Can produce ATP with or without oxygen, in
aerobic or anaerobic conditions
• Fermentation consists of
– Glycolysis + reactions that regenerate NAD+, which can be
reused by glyocolysis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Types of Fermentation
2 ADP + 2
P1
2 ATP
• alcohol fermentation
O–
C O
Glucose
Glycolysis
C O
3C
CH3
2 Pyruvate
2 NADH
2 NAD+
H
2 CO2
– Pyruvate is converted to
ethanol in two steps, one of
which releases CO2
H
H C OH
C O
CH3
2C
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2
Glucose
P1
• lactic acid fermentation
2 ATP
Glycolysis
O–
C O
C O
O
2
NAD+
2 NADH
3C
CH3
C O
3C
H
C OH
CH3
2 Lactate
Figure 9.17
(b) Lactic acid fermentation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Pyruvate is reduced directly
to NADH to form lactate as a
waste product
• Anaerobic metabolism
Electrons
carried
via NADH 2
3x2
2x2
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
lactate
Or
ethanol
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Mitochondrion
2 ATP
Figure 9.6
Electrons carried
via NADH and
FADH2
Substrate-level
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1x2 ATP
Substrate-level
phosphorylation
32-34 ATP
Oxidative
phosphorylation
• Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Acetyl CoA
Citric
acid
cycle
Summaries of Glycolysis
1. anaerobic
Glucose -> 2 Lactate + 2 ATP (lactic acid fermentation)
Glucose -> 2 Ethanol + 2 ATP (alcoholic fermentation)
2. aerobic
Glucose -> 2 Pyruvate + 2ATP + 2NADH (aerobic subtotal)
註: 2 NADH -> 6 ATP (aerobic conversion: 氧化磷酸化)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fermentation and Cellular Respiration Compared
• 相同點
Use glycolysis to oxidize glucose and other
organic fuels to pyruvate
•
相異點
1.Differ in their final electron acceptor
Fermentation by acetylaldehyde (ethanol ferment.); by
pyruvate (lactate ferment.)
Cellular Respiration by O2
2.Cellular respiration produces more ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Evolutionary Significance of Glycolysis
• Glycolysis
– Occurs in nearly all organisms
– Probably evolved in ancient prokaryotes before
there was oxygen in the atmosphere
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.6: Glycolysis and the citric acid
cycle connect to many other metabolic
pathways
The Versatility of Catabolism
• Catabolic pathways
– Funnel electrons from many kinds of organic
molecules into cellular respiration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The catabolism of various molecules from food
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Figure 9.19
Oxidative
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
b-oxidation
Biosynthesis (Anabolic Pathways)
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Regulation of Cellular Respiration via Feedback
Mechanisms
• Cellular respiration is controlled by allosteric
enzymes (e.g., Phosphofructokinase) at key
points in glycolysis and the citric acid cycle
Allosteric regulation (see glossary)
The binding of a molecule to a protein that affects the function of the
protein at a different site.
補充圖
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The control of cellular respiration
Glucose
Glycolysis
Fructose-6-phosphate
–
Inhibits
AMP
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
Citrate
ATP
Acetyl CoA
Citric
acid
cycle
Figure 9.20
Oxidative
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• ATP  AMP + ppi