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Shuttling Energy Sources Across a Membrane!
• Different steps occur in different locations of a cell!
• Resources need to be moved across the mitochondrial membrane
Energy Flow in the EcosystemLightenergy
ECOSYSTEM
Photosynthesisin chloroplasts
Cellular respirationin mitochondria
CO2 H2O O2
Organicmolecules
ATP powersmost cellular workATP
Heatenergy
Catabolic Pathways and ATP Production
The breakdown of organic molecules is exergonic
Fermentation partial sugar degradation without O2
Aerobic respiration consumes organic molecules and O2 and yields ATP
Cellular Respiration
AKA Aerobic Respiration = REQUIRES O2 to complete!
C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat)
-ΔG: -686kcal/mol
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
becomes oxidized(loses electron)
becomes reduced(gains electron)
The Principle of Redox: Transfer of Electrons!
•In oxidation, a substance loses electrons, or is oxidized (becomes more positive)
•In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
More Redox!
becomes oxidized
becomes reduced
Electron donor is called the reducing agent Loses Electrons Oxidized (LEO)
Electron receptor is called the oxidizing agent Gains Electrons Reduced (GER)
Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds
Redox of Methane and Oxygen Gas
Reactants Products
Energy
WaterCarbon dioxideMethane(reducing
agent)
Oxygen(oxidizing
agent)
becomes oxidized
becomes reduced
Oxidation of Organic Fuel Molecules During Cellular Respiration
Fuel (such as glucose) is oxidized, and O2 is reduced
In general lots of C-H bonds make a great fuel source
becomes oxidized
becomes reduced
Carbs: Why Are They Good Energy?Electrons are transferred in the form of H atoms.
C-H bonds are higher in energy. The more C-H bonds the more energy!
C6H12O6 CO2
O2 H2O
Loses Electrons
Gains Electrons
H is transferred from C to O, a lower energy state releases energy for ATP formation
Redox in Respiration Occur in Steps
Enzymes control release of energy by H transfer at key steps!
Not directly to O, but to coenzyme to make more energy first!
Nicotinamide(oxidized form)
NAD
(from food)
Dehydrogenase
Reduction of NAD
Oxidation of NADH
Nicotinamide(reduced form)
NADH
Nicotinamide Adenine Dinucleotide (NAD) and the Energy Harvesting
•Electrons from organic compounds are usually first transferred to NAD+, a coenzyme
•Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP
Electron Removal From Glucose
Dehydrogenase
Sugar-source NAD+
Sugar-source NADH
Released into the surrounding solution
Energy Production in the Electron Transport Chain
(a) Uncontrolled reaction (b) Cellular respiration
Explosiverelease of
heat and lightenergy
Controlledrelease ofenergy for
synthesis ofATP
Fre
e en
erg
y, G
Fre
e en
erg
y, G
H2 1/2 O22 H 1/2 O2
1/2 O2
H2O H2O
2 H+ 2 e
2 e
2 H+
ATP
ATP
ATPE
lectron
transp
ort
chain
(from food via NADH)
The Stages of Cellular Respiration: A Preview
Glycolysis (color-coded teal) glucose to pyruvate 1.
Pyruvate oxidation and the citric acid cycle(color-coded salmon) completes glucose breakdown
2.
Oxidative phosphorylation: electron transport andchemiosmosis (color-coded violet) Most ATP synthesis
3.
Glycolysis
Electronscarried
via NADH
Glycolysis
Glucose Pyruvate
CYTOSOL
MITOCHONDRION
ATP
Substrate-levelphosphorylation
Figure 9.6-2
Electronscarried
via NADH
Electrons carriedvia NADH and
FADH2
Citricacidcycle
Pyruvateoxidation
Acetyl CoA
Glycolysis
Glucose Pyruvate
CYTOSOL MITOCHONDRION
ATP ATP
Substrate-levelphosphorylation
Substrate-levelphosphorylation
Figure 9.6-3
Electronscarried
via NADH
Electrons carriedvia NADH and
FADH2
Citricacidcycle
Pyruvateoxidation
Acetyl CoA
Glycolysis
Glucose Pyruvate
Oxidativephosphorylation:electron transport
andchemiosmosis
CYTOSOL MITOCHONDRION
ATP ATP ATP
Substrate-levelphosphorylation
Substrate-levelphosphorylation
Oxidative phosphorylation
A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation
Substrate-level Phosphorylation
Substrate
Product
ADP
PATP
Enzyme Enzyme
Oxidative Phosphorylation
The sum of all the energy-releasing steps in the mitochondria accounts for almost 90% of the ATP generated
Energy Phases of Glycolysis
Energy Investment Phase
Glucose
2 ADP 2 P
4 ADP 4 P
Energy Payoff Phase
2 NAD+ 4 e 4 H+
2 Pyruvate 2 H2O
2 ATP used
4 ATP formed
2 NADH 2 H+
NetGlucose 2 Pyruvate 2 H2O
2 ATP
2 NADH 2 H+ 2 NAD+ 4 e 4 H+
4 ATP formed 2 ATP used
2 phases: Energy investmentEnergy Payoff
No Carbon released!
Does not depend on oxygen!
Figure 9.9-2
Glycolysis: Energy Investment Phase
ATPGlucose Glucose 6-phosphate Fructose 6-phosphate
ADP
Hexokinase Phosphogluco-isomerase
12
Figure 9.9-3
Glycolysis: Energy Investment Phase
ATP ATPGlucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate
ADP ADP
Hexokinase Phosphogluco-isomerase
Phospho-fructokinase
12 3
Figure 9.9-4
Glycolysis: Energy Investment Phase
ATP ATPGlucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate
Dihydroxyacetonephosphate
Glyceraldehyde3-phosphate
Tostep 6
ADP ADP
Hexokinase Phosphogluco-isomerase
Phospho-fructokinase
Aldolase
Isomerase
12 3 4
5
Figure 9.9-5
Glycolysis: Energy Payoff Phase
2 NADH
2 NAD + 2 H
2 P i
1,3-Bisphospho-glycerate6
Triosephosphate
dehydrogenase
Figure 9.9-6
Glycolysis: Energy Payoff Phase
2 ATP2 NADH
2 NAD + 2 H
2 P i
2 ADP
1,3-Bisphospho-glycerate
3-Phospho-glycerate
2
Phospho-glycerokinase
67
Triosephosphate
dehydrogenase
Figure 9.9-7
Glycolysis: Energy Payoff Phase
2 ATP2 NADH
2 NAD + 2 H
2 P i
2 ADP
1,3-Bisphospho-glycerate
3-Phospho-glycerate
2-Phospho-glycerate
2 2
Phospho-glycerokinase
Phospho-glyceromutase
67 8
Triosephosphate
dehydrogenase
Figure 9.9-8
Glycolysis: Energy Payoff Phase
2 ATP2 NADH
2 NAD + 2 H
2 P i
2 ADP
1,3-Bisphospho-glycerate
3-Phospho-glycerate
2-Phospho-glycerate
Phosphoenol-pyruvate (PEP)
2 2 2
2 H2O
Phospho-glycerokinase
Phospho-glyceromutase
Enolase
67 8
9
Triosephosphate
dehydrogenase
Figure 9.9-9
Glycolysis: Energy Payoff Phase
2 ATP 2 ATP2 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 ADP2 2 2
2 H2O
Phospho-glycerokinase
Phospho-glyceromutase
Enolase Pyruvatekinase
67 8
910
Triosephosphate
dehydrogenase
Glycolysis
Glycolysis: Energy Investment Phase
ATPGlucose Glucose 6-phosphate
ADP
Hexokinase
1
Fructose 6-phosphate
Phosphogluco-isomerase
2
Adds a phosphate = energizing the glucose
Isomerizes the sugar!
Glycolysis: Energy Investment Phase
ATPFructose 6-phosphate
ADP
3
Fructose 1,6-bisphosphate
Phospho-fructokinase
4
5
Aldolase
Dihydroxyacetonephosphate
Glyceraldehyde3-phosphate
Tostep 6Isomerase
Glycolysis
Second energy investment
Cuts the sugar in half!
Switches the 3C sugar between 2 forms
Glycolysis: Energy Payoff Phase
2 NADH2 ATP
2 ADP 2
2
2 NAD + 2 H
2 P i
3-Phospho-glycerate
1,3-Bisphospho-glycerate
Triosephosphate
dehydrogenase
Phospho-glycerokinase
67
Glycolysis
Removes 2 H to make an NADH and H+
Removes a phosphate to make ATP!
Glycolysis: Energy Payoff Phase
2 ATP
2 ADP2222
2 H2O
PyruvatePhosphoenol-pyruvate (PEP)
2-Phospho-glycerate
3-Phospho-glycerate
89
10
Phospho-glyceromutase
Enolase Pyruvatekinase
Glycolysis
Shuffles the phosphate to a different carbon
Pulls off water
Makes more ATP
Oxidation of Pyruvate to Acetyl CoA
This step is carried out by a multienzyme complex that catalyses three reactions to bring pyruvate into the mitochondria
Pyruvate
Transport protein
CYTOSOL
MITOCHONDRION
CO2 Coenzyme A
NAD + HNADH Acetyl CoA
1
2
3
The Citric Acid 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
REMEMBER 2 pyruvate per Glucose!
Pyruvate
NAD
NADH
+ HAcetyl CoA
CO2
CoA
CoA
CoA
2 CO2
ADP + P i
FADH2
FAD
ATP
3 NADH
3 NAD
Citricacidcycle
+ 3 H
• 8 steps, each catalyzed by a specific enzyme
• Acetyl combines with oxaloacetatecitrate
• The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle
Overview: Citric Acid Cycle
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
Citricacidcycle
NADH+ H
NAD
H2O
3
2
CoA-SH
CO2
Oxaloacetate
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
SuccinylCoA
Citricacidcycle
NADH
NADH
+ H
+ H
NAD
NAD
H2O
3
2
4
CoA-SH
CO2
CoA-SH
CO2
Oxaloacetate
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
SuccinylCoA
Succinate
Citricacidcycle
NADH
NADH
ATP
+ H
+ H
NAD
NAD
H2O
ADP
GTP GDP
P i
3
2
4
5
CoA-SH
CO2
CoA-SH
CoA-SH
CO2
Oxaloacetate
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
SuccinylCoA
Succinate
Fumarate
Citricacidcycle
NADH
NADH
FADH2
ATP
+ H
+ H
NAD
NAD
H2O
ADP
GTP GDP
P i
FAD
3
2
4
5
6
CoA-SH
CO2
CoA-SH
CoA-SH
CO2
Oxaloacetate
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
SuccinylCoA
Succinate
Fumarate
Malate
Citricacidcycle
NADH
NADH
FADH2
ATP
+ H
+ H
NAD
NAD
H2O
H2O
ADP
GTP GDP
P i
FAD
3
2
4
5
6
7
CoA-SH
CO2
CoA-SH
CoA-SH
CO2
Oxaloacetate
NADH
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
SuccinylCoA
Succinate
Fumarate
Malate
Citricacidcycle
NAD
NADH
NADH
FADH2
ATP
+ H
+ H
+ H
NAD
NAD
H2O
H2O
ADP
GTP GDP
P i
FAD
3
2
4
5
6
7
8
CoA-SH
CO2
CoA-SH
CoA-SH
CO2
Oxaloacetate
Acetyl CoA
Oxaloacetate
CitrateIsocitrate
H2O
CoA-SH
1
2
Acetyl group (What’s left of the pyruvate) combines with Oxaloacetate to make Citrate
Citrate is isomerized by removing water and then adding it back
Isocitrate
-Ketoglutarate
SuccinylCoA
NADH
NADH
NAD
NAD
+ H
CoA-SH
CO2
CO2
3
4
+ H
Isocitrate is oxidized (Loses 2 H) and reduces NAD+A second reaction occurs, removing CO2
More CO2 is lost, and another NAD+ is reduced. Coenzyme A makes another appearance
Fumarate
FADH2
CoA-SH6
SuccinateSuccinyl
CoA
FAD
ADP
GTP GDP
P i
ATP
5
A phosphate group replaces CoA. The Phosphate is then transferred to GDP to make GTP
Succinate is oxidized by FAD to make FADH2
Oxaloacetate8
Malate
Fumarate
H2O
NADH
NAD
+ H
7 Water molecule added to rearrange bonds
Another redox to make NADH and oxaloacetate
The Pathway of Electron Transport
Occurs in the inner membrane (cristae) of the mitochondrion
Most of the chain’s components are proteins, which exist in multiprotein complexes
The carriers alternate reduced and oxidized states as they accept and donate electrons
NADH
FADH2
2 H + 1/2 O2
2 e
2 e
2 e
H2O
NAD
Multiproteincomplexes
(originally from NADH or FADH2)
III
III
IV
50
40
30
20
10
0
Fre
e e
ner
gy
(G)
rela
tiv
e to
O2 (
kcal
/mo
l)
FMN
FeS FeS
FAD
Q
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
FeS
Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2
no ATP directly generated
Release energy in small steps
NADH and FADH2 Bring electrons to the ETC
Oxidative Phosphorylation and the ETC
Proteincomplexof electroncarriers
(carrying electronsfrom food)
Electron transport chain
Oxidative phosphorylation
Chemiosmosis
ATPsynth-ase
I
II
III
IVQ
Cyt c
FADFADH2
NADH ADP P i
NAD
H
2 H + 1/2O2
H
HH
21
H
H2O
ATP
Electron transfer is coupled with H+ pumping into intermembrane space of mitchondria
Chemiosmosis: Energy-Coupling Mechanism
Using H+ Gradient to do Work
INTERMEMBRANE SPACE
Rotor
StatorH
Internalrod
Catalyticknob
ADP+P i ATP
MITOCHONDRIAL MATRIX
The H+ gradient is referred to as a proton-motive force
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
H+ generated by ETC coupled with ATP synthesis!
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 32-36 ATP
There are several reasons why the number of ATP is not known exactly
Figure 9.16
Electron shuttlesspan membrane
MITOCHONDRION2 NADH
2 NADH 2 NADH 6 NADH
2 FADH2
2 FADH2
or
2 ATP 2 ATP about 26 or 28 ATP
Glycolysis
Glucose 2 Pyruvate
Pyruvate oxidation
2 Acetyl CoACitricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
CYTOSOL
Maximum per glucose:About
30 or 32 ATP
Anaerobic Respiration
Oxygen is not used or may be poisonous!
Certain fungi and bacteria undergo Glycolysis coupled to an electron transport chain but use other molecules as final electron acceptors like sulfate!
Fermentation: Anaerobic Respiration Using Substrate Level Phosphorylation
Fermentation consists of glycolysis plus reactions that regenerate NAD+
Without NAD+ Glycolysis couldn’t happen
Fermentation
2 ADP 2 ATP
Glucose Glycolysis
2 Pyruvate
2 CO22
2 NADH
2 Ethanol 2 Acetaldehyde
(a) Alcohol fermentation (b) Lactic acid fermentation
2 Lactate
2 Pyruvate
2 NADH
Glucose Glycolysis
2 ATP2 ADP 2 Pi
NAD
2 H
2 Pi
2 NAD
2 H
In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2
In lactic acid fermentation, pyruvate is reduced to NADH, forming lactate with no release of CO2
2 ADP 2 P i 2 ATP
Glucose Glycolysis
2 Pyruvate
2 CO22 NAD
2 NADH
2 Ethanol 2 Acetaldehyde
(a) Alcohol fermentation
2 H
Figure 9.17a
(b) Lactic acid fermentation
2 Lactate
2 Pyruvate
2 NADH
Glucose Glycolysis
2 ADP 2 P i 2 ATP
2 NAD
2 H
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt, and human muscles when O2 is scarce
Importance of Pyruvate
Glucose
CYTOSOLGlycolysis
Pyruvate
No O2 present:Fermentation
O2 present: Aerobic cellular respiration
Ethanol,lactate, or
other products
Acetyl CoA
MITOCHONDRION
Citricacidcycle
Obligate anaerobes – Oxygen is poisonous!
Facultative anaerobes – can go either way
CarbohydratesProteins
Fattyacids
Aminoacids
Sugars
Fats
Glycerol
Glycolysis
Glucose
Glyceraldehyde 3- P
NH3 Pyruvate
Acetyl CoA
Citricacidcycle
Oxidativephosphorylation
Catabolism of Various Food
Sources
Glycolysis accepts a wide range of carbohydrates
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
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
Feedback Mechanisms and Cell Respiration
Phosphofructokinase
Glucose
GlycolysisAMP
Stimulates
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Pyruvate
Inhibits Inhibits
ATP Citrate
Citricacidcycle
Oxidativephosphorylation
Acetyl CoA
•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
Fermentation vs. Anaerobic vs. Aerobic Respiration
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
Figure 9.UN07
Inputs Outputs
2 Pyruvate 2 Acetyl CoA
2 OxaloacetateCitricacidcycle
2
26
8ATP NADH
FADH2CO2
Figure 9.UN08
Protein complexof electroncarriers
(carrying electrons from food)
INTERMEMBRANESPACE
MITOCHONDRIAL MATRIX
H
HH
2 H + 1/2 O2 H2O
NAD
FADH2 FAD
Q
NADH
I
II
III
IV
Cyt c