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Lesson 7: Harvesting of Energy “Cellular Respiration”

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1 Lesson 7: Harvesting of Energy “Cellular Respiration”
March 2, 2015

2 Where Is Our Energy Derived????
Resources of Energy

3 Photosynthesis vs Cellular Respiration
Organisms can be classified based on how they obtain energy: Autotrophs Able to produce their own organic molecules through photosynthesis Heterotrophs Live on organic compounds produced by other organisms ALL organisms use cellular respiration to extract energy from organic molecules

4 Cellular Respiration Cellular respiration—the set of metabolic reactions and processes in the cells of organisms that convert biochemical energy from nutrients into ATP Cycles between redox reactions Oxidations – loss of electrons Reductions—gain of electrons Dehydrogenations – lost electrons are accompanied by protons A hydrogen atom is lost (1 electron, 1 proton)

5 Redox During redox reactions, electrons carry energy from one molecule to another Nicotinamide adenosine dinucleotide (NAD+) An electron carrier NAD+ accepts 2 electrons and 1 proton to become NADH Reaction is reversible


7 Overview of Cellular Respiration
During the cellular energy harvest Dozens or redox reactions take place Number of electron acceptors including NAD+ In the end, high-energy electrons from initial chemical bonds have lost much of their energy Transferred to a final electron acceptor Final electron acceptor is dependent on the organism

8 Final Electron Acceptors
Aerobic respiration Final electron receptor is oxygen (O2) Anaerobic respiration Final electron acceptor is an inorganic molecule (not O2) Sulfur Iron (Fe) Fermentation Final electron acceptor is an organic molecule Ethanol fermentation

9 Aerobic respiration C6H12O6 + 6O2 6CO2 + 6H2O
DG = -686kcal/mol of glucose This large amount of energy must be released in small steps rather than all at once.


11 Electron Carriers Many types of protein carriers are used
Soluble, membrane-bound, move within membrane All carriers can be easily oxidized and reduced Some carry only electrons; others carry both electrons and protons NAD+ acquires 2 electrons and a proton to become NADH


13 ATP Cells use ATP to drive endergonic reactions
2 mechanisms for synthesis of ATP Substrate-level phosphorylation Transfer phosphate group directly to ADP During glycolysis stage of cellular respiration Oxidative phosphorylation ATP synthase uses energy from a proton gradient to generate ATP

14 Oxidation of Glucose The complete oxidation of glucose proceeds in stages: 1. Glycolysis 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain & chemiosmosis


16 Play Animation From Beginning through Glycolysis

17 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+



20 NADH Must Be Recycled For glycolysis to continue, NADH must be recycled to NAD+ by either: Aerobic respiration Oxygen is available as the final electron acceptor Produces significant amount of ATP Fermentation Occurs when oxygen is not available Organic molecule is the final electron acceptor EtOh

21 Play Animation Citric Acid Cycle (Krebs Cycle)

22 Fate of Pyruvate Depends on oxygen availability.
When oxygen is present, pyruvate is oxidized to acetyl-CoA which enters the Krebs cycle Aerobic respiration Without oxygen, pyruvate is reduced in order to oxidize NADH back to NAD+ Fermentation


24 Pyruvate Oxidation In the presence of oxygen, pyruvate is oxidized
Occurs in the mitochondria in eukaryotes Multi-enzyme complex called pyruvate dehydrogenase catalyzes the reaction Occurs at the plasma membrane in prokaryotes

25 Products of Pyruvate Oxidation
For each 3 carbon pyruvate molecule: 1 CO2 Decarboxylation by pyruvate dehydrogenase 1 NADH 1 acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A Acetyl-CoA proceeds to the Krebs cycle


27 Krebs Cycle Oxidizes the acetyl group from pyruvate
Occurs in the matrix of the mitochondria Biochemical pathway of 9 steps in three segments Acetyl-CoA + oxaloacetate → citrate Citrate rearrangement and decarboxylation Regeneration of oxaloacetate


29 Krebs Cycle For each Acetyl-CoA entering: Release 2 molecules of CO2
Reduce 3 NAD+ to 3 NADH Reduce 1 FAD (electron carrier) to FADH2 Produce 1 ATP Regenerate oxaloacetate


31 At This Point….. Glucose has been oxidized to: 6 CO2 4 ATP 10 NADH
2 FADH2 These electron carriers proceed to the electron transport chain

32 Play Animation Electron Transport Chain to the end.

33 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


35 Chemiosmosis Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion Membrane “relatively” impermeable to ions Most protons can only re-enter matrix through ATP synthase Uses energy of gradient to make ATP from ADP + Pi



38 Energy Yield of Respiration
Theoretical energy yield 38 ATP per glucose for bacteria 36 ATP per glucose for eukaryotes Actual energy yield ≈30 ATP per glucose for eukaryotes Reduced yield is due to “Leaky” inner membrane Use of the proton gradient for purposes other than ATP synthesis


40 Glucose’s Role in Diabetes
Glucose Uptake Into Cells

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