LE 8-8
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Transcript of LE 8-8
LE 8-8
Phosphate groups
Ribose
Adenine
Using Hydrolysis to
break the phosphate bond
LE 8-9
Adenosine triphosphate (ATP)
Energy
P P P
PPP i
Adenosine diphosphate (ADP)Inorganic phosphate
H2O
+ +
How ATP Performs Work• ATP drives endergonic reactions by
phosphorylation, transferring a phosphate group to some other molecule, such as a reactant
• The recipient molecule is now phosphorylated• The three types of cellular work (mechanical,
transport, and chemical) are powered by the hydrolysis of ATP
LE 8-11
NH2
Glu
P i
P i
P i
P i
Glu NH3
P
P
P
ATPADP
Motor protein
Mechanical work: ATP phosphorylates motor proteins
Protein moved
Membraneprotein
Solute
Transport work: ATP phosphorylates transport proteins
Solute transported
Chemical work: ATP phosphorylates key reactants
Reactants: Glutamic acidand ammonia
Product (glutamine)made
+ +
+
LE 9-2
ECOSYSTEM
Lightenergy
Photosynthesisin chloroplasts
Cellular respirationin mitochondria
Organicmolecules+ O2
CO2 + H2O
ATP
powers most cellular work
Heatenergy
Several processes are central to cellular respiration and related pathways
Production of ATP• The breakdown of organic molecules is
exergonic• Fermentation is a partial degradation of sugars
that occurs without oxygen• Cellular respiration consumes oxygen and
organic molecules and yields ATP• Although carbohydrates, fats, and proteins are all
consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:
C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP + heat)
• The transfer of electrons during chemical reactions releases energy stored in organic molecules
• This released energy is ultimately used to synthesize ATP
• During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced:
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
becomes oxidized
becomes reduced
the Electron Transport Chain• In cellular respiration, glucose and other
organic molecules are broken down in a series of steps
• Electrons from organic compounds are usually first transferred to NAD+, a coenzyme
• As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration
• Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP
• 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
• Oxygen pulls electrons down the chain in an energy-yielding tumble
• The energy yielded is used to regenerate ATP
LE 9-5
2 H+ + 2 e–
2 H
(from food via NADH)
Controlledrelease ofenergy for
synthesis ofATP ATP
ATP
ATP
2 H+
2 e–
H2O
+ 1/2 O21/2 O2H2 +
1/2 O2
H2O
Explosiverelease of
heat and lightenergy
Cellular respirationUncontrolled reaction
Fre
e en
erg
y, G
Fre
e en
erg
y, G
Electro
n tran
spo
rt chain
The Stages of Cellular Respiration: A Preview
• Cellular respiration has three stages:– Glycolysis (breaks down glucose into two
molecules of pyruvate)
– Kreb’s cycle
– Electron Transport System
• The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
LE 9-6_1
Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
LE 9-6_2
Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
ATP
Substrate-levelphosphorylation
Kreb’sCycle
LE 9-6_3
Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
ATP
Substrate-levelphosphorylation
Krebscycle
ATP
Oxidativephosphorylation
Oxidativephosphorylation:electron transport
andchemiosmosis
Electronscarried
via NADH
Electrons carriedvia NADH and
FADH2
• Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration (electron transport system)
• A small amount of ATP is formed in glycolysis and the Krebs cycle
Glycolysis harvests 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
LE 9-8
Energy investment phase
Glucose
2 ATP used2 ADP + 2 P
4 ADP + 4 P 4 ATP formed
2 NAD+ + 4 e– + 4 H+
Energy payoff phase
+ 2 H+2 NADH
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
Net
Glycolysis Citricacidcycle
Oxidativephosphorylation
ATPATPATP
LE 9-9a_1
Glucose
ATP
ADP
Hexokinase
ATP ATP ATP
Glycolysis Oxidationphosphorylation
Citricacidcycle
Glucose-6-phosphate
LE 9-9a_2
Glucose
ATP
ADP
Hexokinase
ATP ATP ATP
Glycolysis Oxidationphosphorylation
Citricacidcycle
Glucose-6-phosphate
Phosphoglucoisomerase
Phosphofructokinase
Fructose-6-phosphate
ATP
ADP
Fructose-1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
LE 9-9b_1
2 NAD+
Triose phosphatedehydrogenase
+ 2 H+
NADH2
1, 3-Bisphosphoglycerate
2 ADP
2 ATPPhosphoglycerokinase
Phosphoglyceromutase
2-Phosphoglycerate
3-Phosphoglycerate
LE 9-9b_2
2 NAD+
Triose phosphatedehydrogenase
+ 2 H+
NADH2
1, 3-Bisphosphoglycerate
2 ADP
2 ATPPhosphoglycerokinase
Phosphoglyceromutase
2-Phosphoglycerate
3-Phosphoglycerate
2 ADP
2 ATPPyruvate kinase
2 H2OEnolase
Phosphoenolpyruvate
Pyruvate
The Krebs cycle completes the energy-yielding oxidation of
organic molecules
• Before the Krebs cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis
LE 9-10
CYTOSOL
Pyruvate
NAD+
MITOCHONDRION
Transport protein
NADH + H+
Coenzyme ACO2
Acetyl Co A
• The Krebs cycle, takes place within the mitochondrial matrix
• The cycle oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH2 per turn
LE 9-11Pyruvate(from glycolysis,2 molecules per glucose)
ATP ATP ATP
Glycolysis Oxidationphosphorylation
CitricacidcycleNAD+
NADH
+ H+
CO2
CoA
Acetyl CoACoA
CoA
Krebscycle CO2
2
3 NAD+
+ 3 H+
NADH3
ATP
ADP + P i
FADH2
FAD
• The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain
• Following glycolysis and the Krebs 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
The Pathway of Electron Transport
• The electron transport chain is in the 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
• Electrons drop in free energy as they go down the chain and are finally passed to O2, forming water
• The electron transport chain 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
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 channels in ATP synthase
• ATP synthase uses the flow of H+ to drive phosphorylation of ATP
• This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work
LE 9-14
INTERMEMBRANE SPACE
H+ H+
H+H+
H+
H+
H+
H+
ATP
MITOCHONDRAL MATRIX
ADP+
Pi
A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient.
A stator anchored in the membrane holds the knob stationary.
A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob.
Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.
LE 9-15
Protein complexof electroncarriers
H+
ATP ATP ATP
GlycolysisOxidative
phosphorylation:electron transportand chemiosmosis
Citricacidcycle
H+
Q
IIII
II
FADFADH2
+ H+NADH NAD+
(carrying electronsfrom food)
Innermitochondrialmembrane
Innermitochondrialmembrane
Mitochondrialmatrix
Intermembranespace
H+
H+
Cyt c
IV
2H+ + 1/2 O2 H2O
ADP +
H+
ATP
ATPsynthase
Electron transport chainElectron transport and pumping of protons (H+),
Which create an H+ gradient across the membrane
P i
ChemiosmosisATP synthesis powered by the flow
of H+ back across the membrane
Oxidative phosphorylation
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 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP
LE 9-16
CYTOSOL Electron shuttlesspan membrane 2 NADH
or
2 FADH2
MITOCHONDRION
Oxidativephosphorylation:electron transport
andchemiosmosis
2 FADH22 NADH 6 NADH
Citricacidcycle
2AcetylCoA
2 NADH
Glycolysis
Glucose2
Pyruvate
+ 2 ATP
by substrate-levelphosphorylation
+ 2 ATP
by substrate-levelphosphorylation
+ about 32 or 34 ATP
by oxidation phosphorylation, dependingon which shuttle transports electronsform NADH in cytosol
About36 or 38 ATPMaximum per glucose:
Fermentation enables some cells to produce ATP without the use
of oxygen
• Cellular respiration requires O2 to produce ATP
• Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)
• In the absence of O2, glycolysis couples with fermentation to produce ATP
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
• 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
LE 9-17a
CO2
+ 2 H+
2 NADH2 NAD+
2 Acetaldehyde
2 ATP2 ADP + 2 P i
2 Pyruvate
2
2 Ethanol
Alcohol fermentation
Glucose Glycolysis
• 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
LE 9-17b
CO2
+ 2 H+
2 NADH2 NAD+
2 ATP2 ADP + 2 P i
2 Pyruvate
2
2 Lactate
Lactic acid fermentation
Glucose Glycolysis
Fermentation and Cellular Respiration Compared
• Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate
• The processes have different final electron acceptors: an organic molecule (such as pyruvate) in fermentation and O2 in cellular respiration
• Cellular respiration produces much more ATP
LE 9-18
Pyruvate
Glucose
CYTOSOL
No O2 presentFermentation
Ethanolor
lactate
Acetyl CoA
MITOCHONDRION
O2 present Cellular respiration
Citricacidcycle
Concept 9.6: Glycolysis and the citric acid cycle connect to many
other metabolic pathways
• Gycolysis and the Krebs cycle are major intersections to various catabolic and anabolic pathways
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• Fats are digested to glycerol (used in glycolysis)
and fatty acids (used in generating acetyl CoA) • An oxidized gram of fat produces more than twice
as much ATP as an oxidized gram of carbohydrate
LE 9-19
Citricacidcycle
Oxidativephosphorylation
Proteins
NH3
Aminoacids
Sugars
Carbohydrates
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
Fattyacids
Glycerol
Fats