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Energy Use in Cells
Glycolysis, Krebs’s Cycle, Electron Transport, Fermentation &
Metabolism
Glycolysis
– a single molecule of glucose is enzymatically cut in half through a series of steps,
– two molecules of pyruvate are produced,– two molecules of NAD+ are reduced to two
molecules of NADH, and– a net of two molecules of ATP is produced.
Figure 6.7A
Glucose
2 Pyruvate
2 ADP
2 P2 NAD
2 NADH
2 HATP2
Figure 6.7Ca_s2Glucose
Glucose 6-phosphate
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Glyceraldehyde3-phosphate (G3P)
ENERGYINVESTMENT
PHASE
PP
P P
P
P
ADP
ADP
ATP
ATP
StepSteps – A fuelmolecule is energized,using ATP.
Step A six-carbonintermediate splitsinto two three-carbonintermediates.
4
4
3
3
2
1
1
Figure 6.7Cb_s2
6 6 6
5 5 5
9
9 9
8 8
7 7
Step A redox reactiongenerates NADH.
Steps – ATP and pyruvateare produced.
ENERGYPAYOFFPHASE
1,3-Bisphospho-glycerate
3-Phospho-glycerate
2-Phospho-glycerate
Phosphoenol-pyruvate (PEP)
Pyruvate
NADH NADH
NADNAD
H H
ADP ADP
ADP ADP
ATP ATP
ATP ATP
H2O H2O
P P
P
P P
P
P
P
P
P P
P
P
P
The Krebs Cycle Releases Carbon Dioxide and Generates Energy Carriers• Pyruvate entering the mitochondrion must be
broken down into acetyl CoA before entering the Krebs Cycle
• Through a series of reactions, the Krebs cycle produces ATP, NADH, and FADH2, energy carriers that will be used in the final stage of cellular respiration
Figure 6.8
Pyruvate
Coenzyme A
Acetyl coenzyme A
NAD NADH H
CoA
CO2
3
2
1
Figure 6.9AAcetyl CoA
Citric Acid Cycle
CoA
CoA
CO22
3
3
NAD
3 H
NADH
ADPATP P
FAD
FADH2
The Krebs’s Cycle
• Remember that the citric acid cycle processes two molecules of acetyl CoA for each initial glucose.
• Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is– 2 ATP,– 6 NADH, and– 2 FADH2.
Oxidative Phosphorylation Uses Oxygen to Produce ATP in Quantity• Oxidative phosphorylation produces the
largest amount of ATP during cellular respiration
• Oxidative phosphorylation is the last stage of cellular respiration and takes place in the many folds (cristae) of the inner mitochondrial membrane
Oxidative Phosphorylation Uses Oxygen to Produce ATP in Quantity
• Energy carriers produced during the Krebs cycle donate their high-energy electrons to the electron transport chain (ETC), which releases energy as it passes electrons down the chain
• The energy released from the ETC is used to create a proton gradient
Oxidative Phosphorylation Uses Oxygen to Produce ATP in Quantity
• The movement of protons through the ATP synthase channel activates enzymes that catalyze the phosphorylation of ADP to from ATP
• Electrons that travel down the ETC are eventually accepted by O2 and H+ to make water
• Cellular respiration has a net yield of about 30 to 32 ATP molecules per molecule of glucose
Figure 6.12
NADH
FADH2
NADH FADH2NADH
orNADH
MitochondrionCYTOPLASM
Electron shuttlesacross membrane
Glycolysis
Glucose2
Pyruvate
PyruvateOxidation2 Acetyl
CoA
Citric AcidCycle
OxidativePhosphorylation
(electron transportand chemiosmosis)
Maximumper glucose:
by substrate-levelphosphorylation
by substrate-levelphosphorylation
by oxidativephosphorylation
2
2
2
2
6 2
ATP 2 about
28 ATP AboutATP32
ATP 2
Fermentation Facilitates ATP Production Through Glycolysis When Oxygen Is Absent
• Glycolysis does not require oxygen; it is an anaerobic process
• During fermentation, the pyruvate and NADH produced by glycolysis remain in the cytosol
• Postglycolytic reactions convert pyruvate and NADH into other molecules, such as alcohol or lactic acid
Fermentation Facilitates ATP Production Through Glycolysis When Oxygen Is Absent
• Fermentation by anaerobic yeasts converts pyruvate into an ethanol, releasing CO2 gas
• Lactic acids forms in severely taxed muscle cells as a result of ATP production in the absence of oxygen
Figure 6.13B
2 NAD
2 NADH
2 NAD
2 NADH
2 Ethanol
2 Pyruvate
Glucose
2 ADP
2 ATP
2 P
Gly
coly
sis
2 CO2
p. 101
Figure 6.13A
2 NAD
2 NADH
2 NAD
2 NADH
2 Lactate
2 Pyruvate
Glucose
2 ADP
2 ATP
2 P
Gly
coly
sis
Figure 6.15_1
Sugars GlycerolFatty acids Amino acids
Aminogroups
OxidativePhosphorylation
CitricAcidCycle
PyruvateOxidationAcetyl CoA
Glucose G3P Pyruvate
Glycolysis
Carbohydrates
ATP
Fats Proteins
Food
Figure 6.16_1
CarbohydratesFatsProteins
Cells, tissues, organisms
Amino acids Fatty acidsGlycerol Sugars
Aminogroups
CitricAcidCycle
PyruvateOxidationAcetyl CoA
ATP neededto drivebiosynthesis
ATP
Glucose SynthesisPyruvate G3P Glucose