Cellular Respiration: Harvesting Chemical Energy
Energy Flows through the Ecosystem
CO2
H2O
Glucose
O2
ATP
ECOSYSTEM
Sunlight energy
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
(for cellular work)
Heat energy
+! +!
Energy enters the ecosystem in form of solar energy
Photosynthesis converts solar energy to chemical energy. Glucose and O2 are produced from CO2 and H2O Cellular respiration converts chemical energy from food to ATP. Glucose is oxidized to CO2 and H2O
With each conversion of energy, some energy gets lost as heat
Redox Reactions (oxidation and reduction simultaneously occur in a chemical reaction)
The human body uses energy from ATP for all its activities
Cells need ATP
! ATP powers • active transport • Mechanical work (movement) • Anabolic (endergonic) reactions
Cellular Respiration
Oxidative phosphorylation
Substrate-level phosphorylation
Substrate-level phosphorylation
Glycolysis Glucose and other
fuel molecules
Pyruvate
Pyruvate oxidation
Acetyl-CoA
Citric acid cycle
Electrons carried by NADH and FADH2
Electron transfer system and oxidative
phosphorylation
Mito
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Cellular Respiration occurs in three stages
Citric acid cycle
Glycolysis
Pyruvate oxidation
Oxidative phosphorylation
ATP
ATP
ATP
Cytosol
Glucose
2 Pyruvate
Oxidation
In glycolysis, glucose is oxidized to pyruvate.
The electrons from that reaction reduce NAD+ to NADH.
NADH carries the electrons to be used in the oxidative phosphorylation
In Glycolysis and the Citric Acid Cycle, ATP is produced by Substrate Level Phosphorylation
Enzyme
ADP
P
Substrate
Product
Enzyme
ATP +
Substrate
Product
The Electron Carrier NAD+ can pick up 2 electrons
Pyruvate is transported into the mitochondrial matrix as Acetyl-CoA
Acetyl CoA (acetyl coenzyme A)
Coenzyme A
Pyruvate
CO2
NAD+ NADH H+
CoA
+
Glycolysis
NADH must be recycled
! For glycolysis to continue, NADH must be recycled to NAD+ by either:
1. Aerobic respiration • Oxygen is available as the final electron
acceptor • Produces significant amount of ATP
2. Fermentation • Occurs when oxygen is not available • Organic molecule is the final electron acceptor
Summary Glycolysis
! Converts 1 glucose (6 carbons) to 2 pyruvate (3 carbons)
! 10-step biochemical pathway ! Occurs in the cytoplasm ! Net production of 2 ATP molecules by substrate-
level phosphorylation ! 2 NADH produced by the reduction of NAD+
The Pyruvate needs “grooming” for the next step
Citric acid cycle
Glycolysis
Pyruvate oxidation
Oxidative phosphorylation
Mitochondrial matrix
Pyruvate is transported into the mitochondrial matrix as Acetyl-CoA
Pyruvate
Acetyl-CoA
Mitochondria, Sites of Cellular Respiration Acetyl-CoA
Summary of Krebs Cycle (Citric Acid Cycle) Reactions
! For each Acetyl-CoA entering the Krebs Cycle: • 2 molecules of CO2 are released
• 3 NAD+ are reduced to 3 NADH
• 1 FAD (electron carrier) is reduced to FADH2 • • 1 ATP is produced
• The initial acceptor molecule Oxaloacetate is regenerated
Pyruvate
Acetyl-CoA
Citric acid cycle
The last step of Cellular Respiration: Oxidative Phosphorylation
Citric acid cycle
Glycolysis
Pyruvate oxidation
Oxidative phosphorylation
Inner mitochondrial membrane
Oxidative Phosporylation consists of the Electron transport chain and Chemiosmosis
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Electron Transport Chain
! ETC is a series of membrane-bound electron carriers
! Embedded in the inner mitochondrial membrane ! Electrons from NADH and FADH2 are transferred
to complexes of the ETC ! Each complex • A proton pump creating proton gradient • Transfers electrons to next carrier
Why Electron Transport?
2 H+ + 2 e–
2 H
(from food via NADH)
Controlled release of energy for
synthesis of ATP
ATP
ATP
ATP
2 H+
2 e–
H2O
+ 1/2 O2
1/2 O2
Cellular respiration
Free
ene
rgy,
G Electron transport chain
1/2 O2 H2
+
H2O
Explosive release of
heat and light energy
Uncontrolled reaction
Free
ene
rgy,
G
H2 + ! O2 2 H + ! O2
2 H+
2 e!
2 e! 2 H+ +
H2O
! O2
Controlled release of
energy
Electron transport
chain
ATP
ATP
ATP
Explosive release
Cellular respiration Uncontrolled reaction (a) (b)
Free
ene
rgy,
G
Free
ene
rgy,
G
H2O
Chemiosmosis
! Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion
! Membrane relatively impermeable to ions ! Most protons can only reenter matrix through
ATP synthase • Uses energy of gradient to make ATP from ADP +
Pi
Overview Cellular Respiration Inhibitors of the Electron Transport Chain
H+
H+
H+
H+
H+
H+ H+ H+ H+
H+
H+
H+ H+
O2
H2O P ATP
NADH NAD+
FADH2 FAD
ATP Synthase
+! 2
ADP +!
Electron Transport Chain Chemiosmosis
1 2
Rotenone Cyanide, carbon monoxide
Oligomycin
DNP
Summary: Glycolysis, Citric Acid Cycle and Oxidative Phosphorylation
CYTOSOL Electron shuttles span membrane 2 NADH
or
2 FADH2
MITOCHONDRION
Oxidative phosphorylation: electron transport
and chemiosmosis
2 FADH2 2 NADH 6 NADH
Citric acid
cycle
2 Acetyl CoA
2 NADH
Glycolysis
Glucose 2
Pyruvate
+ 2 ATP
by substrate-level phosphorylation
+ 2 ATP
by substrate-level phosphorylation
+ about 32 or 34 ATP
by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol
About 36 or 38 ATP Maximum per glucose:
The actual yield is about 30 ATP per molecule of glucose due to leaky membranes
The Fate of Pyruvate is Dependent on Oxygen Availability
Fermentation occurs when oxygen is not available
Glucose
Pyruvate
Glycolysis
Lactate
Alcoholic Fermentation
Glucose
Pyruvate
Glycolysis
Ethanol
Fermentation replenishes NAD+ to further drive Glycolysis
Cells use many kinds of organic molecules as fuel for cellular respiration (catabolic processes)
OXIDATIVE PHOSPHORYLATION
(Electron Transport and Chemiosmosis)
Food, such as peanuts
Carbohydrates Fats Proteins
Sugars Glycerol Fatty acids Amino acids
Amino groups
Glucose G3P Pyruvate Acetyl CoA
CITRIC ACID
CYCLE
ATP
GLYCOLYSIS
Food molecules provide raw materials for biosynthesis (anabolic processes)
ATP needed to drive biosynthesis
ATP
CITRIC ACID
CYCLE
GLUCOSE SYNTHESIS
Acetyl CoA
Pyruvate G3P Glucose
Amino groups
Amino acids Fatty acids
Glycerol Sugars
Carbohydrates Fats Proteins
Cells, tissues, organisms