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Transcript of Energy metabolism Photosynthesis –Uses light as source of energy to make organic molecules from CO...
![Page 1: Energy metabolism Photosynthesis –Uses light as source of energy to make organic molecules from CO 2 and H 2 O Respiration –Uses organic molecules and.](https://reader036.fdocuments.net/reader036/viewer/2022062518/56649dbc5503460f94aadddb/html5/thumbnails/1.jpg)
Energy metabolism
Photosynthesis– Uses light as source of energy to make
organic molecules from CO2 and H2O
Respiration – Uses organic molecules and O2 as source
of energy, producing CO2 and H2O
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These pathways involve redox (reduction- oxidation) reactions
• Remember OIL RIG oxidation is loss of electrons, reduction is gain
• When electrons leave an atom, it is "oxidized“.
• When they approach an atom,it is "reduced“.
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Electronegativity
• Some elements attract shared electrons more strongly than others
• The most stable (low energy) covalent bonds are those that allow electrons to get close to electronegative atoms, therefore...
• The most stable bonds are those between strongly and weakly electronegative atoms.
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Oxidation
• Recall that oxygen is very electronegative, relative to carbon, hydrogen.
• organic molecules can react with oxygen, giving CO2 and H2O because…..
• -C-C, -C-H, O=O bonds are less stable (higher energy) than O=C=O (carbon dioxide) and H-O-H (water)
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Combustion and the terms “reduction” and “oxidation”
• CH4 + 2 O2 CO2 + 2 H2O + heat
• Combustion was the first redox reaction described- what burned was said to be "oxidized" because it combined with oxygen
• Oxygen was "reduced" because the O2 gas volume was reduced (got smaller).
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Methane combustion as a redox reaction
A “redox” reaction moves electrons closer to electronegative atoms (e.g. oxygen).
The blue dots represent the shared electrons, and the lines represent the covalent bonds in the compounds
CH4 + 2 (O2) CO2 + 2 (H2O) + heat
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H2 + O2 → H2O + heat
Spectacular example of redox reaction at Lakehurst, New Jersey
May 6,1937
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Redox reactions don’t have to involve oxygen
• A “redox” reaction is just one that moves electrons closer to an electronegative atom.
• The electrons may come along with a hydrogen atom or some other atom or, in some reactions, may go by themselves
• Most chemical reactions in energy metabolism are redox reactions
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The Fire of Life
• The net reaction for the oxidation of glucose is:
C6H12O6 + 6(O2) ↔ 6(CO2) + 6(H2O) + 686 kcal/mole
• The net reaction can occur by combustion or as the net result of a metabolic pathway.
• In metabolism, about 37% of the energy is “trapped” temporarily in chemical intermediates
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Respiration
• Organic molecules are oxidized in a stepwise series of reactions that “traps energy” in chemical products, including:
• NADH nicotinamide adenine dinucleotide
• ATP adenosine triphosphate
• These compounds are reactants in metabolic pathways that accomplish energy-requiring processes
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NADH redox reaction
NAD+ + 2H (from food) ↔ NADH + H+
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nicotine
amide
nicotinamide
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NADH is an electron shuttle
• Electrons from food transferred to NADH, which then transfers them to proteins
• This starts a metabolic pathway of redox reactions (the “electron transport chain”) that leads to ATP
• Eventually the electrons (and H) reach oxygen, forming water.
• NADH is also used in synthetic reactions
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Respiration: three parts• Glycolysis
makes some ATP and NADH
• Krebs cycle makes a lot of NADH & FADH2
• Electron transport and oxidative phosphorylation
uses NADH and FADH2 to make lots of ATP
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An overview of cellular respiration (Layer 1)
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An overview of cellular respiration (Layer 2)
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An overview of cellular respiration (Layer 3)
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Glycolysis
• 10 enzyme-catalyzed steps in the cell cytoplasm
• Uses only glucose as fuel
• Net 2 ATP and 2 NADH per glucose
• Produces 2 pyruvate molecules
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A closer look at glycolysis: energy investment phase (Layer 2)
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A closer look at glycolysis: energy payoff phase (Layer 3)
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A closer look at glycolysis: energy payoff phase (Layer 4)
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Substrate-level phosphorylation of ATP in glycolysis
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So, what happens to pyruvate?
• pyruvate enters the mitochondrion
• A 3 reaction path generates NADH, loses the carboxyl as CO2, and links the remaining 2-carbon group (acetyl) to coenzyme A
• The acetyl-co-A passes acetyl into the metabolic pathway called Krebs cycle
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Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle
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Coenzyme A
Acetyl-coenzyme A
“CoA “ in previous diagram
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Kreb’s cycle
• Also called TCA or citrate cycle
• 8 enzyme-catalyzed steps in the mitochondrion.
• Cyclical because the last product (oxaloacetate) is one of the first reactants
• Produces ATP, NADH, FADH2 and CO2
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A summary of the Krebs cycle
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A closer look at the Krebs cycle (Layer 4)
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Electron transport chain
• Series of 9 proteins and one lipid bound to the inner mitochondrial membrane
• Undergo redox reactions starting with NADH and FADH2
• These redox reactions are coupled to the active transport of H+
across the inner membrane.
• Creates electrochemical gradient of H+,
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Chemiosmosis couples the electron transport chain to ATP synthesis
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This diagram shows the free energy potential of the components of the electron transport chain, relative to O2
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ATP synthase
F0 unit
F1 unit
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ATP synthase mechanism- wow!
• Proton flow powers clockwise rotation of the F0 unit and central rod.
• Rotation causes active sites on F1 to crunch ADP and Pi together into ATP.
• Nobel prize in 1997 to Paul Boyer (UCLA) and John Walker (Cambridge)http://www.nobel.se/chemistry/laureates/1997/index.html
• Link to videos by Wolfgang Junge:http://www.biologie.uni-osnabrueck.de/Biophysik/junge/picsmovs.html
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Photo of ATP synthase on chloroplast membrane
Animated model of the conformational changes in the F1 unit of ATP synthase
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Isolated F1 units can also spin the central rod (opposite direction) by hydrolyzing ATP – they might be used as nanomotors for nanomachines.
Related news link (if you are interested):http://www.news.cornell.edu/releases/Nov00/propeller.hrs.html
ATP
ADP + Pi
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Review: how each molecule of glucose yields many ATP molecules during cellular respiration
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What if there is no oxygen?
• Anaerobic energy metabolism uses glycolysis and fermentation to produce ATP without respiration.
• Glycolysis produces ATP and NADH
• Fermentation reactions recycle NADH to NAD+ and remove pyruvate so that glycolysis can continue.
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Fermentation
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Fermentation
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Aerobic energy metabolism
• High efficiency: ~36 ATP per glucose
• High endurance: carbohydrates, fat, and protein can all be used.
• End products (CO2 and water) are carried away easily.
• Low power: rate of ATP production is limited by the ability of cardiovascular system to deliver O2 to mitochondria.
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Anaerobic energy metabolism
• Glycolysis plus fermentation
• Low efficiency: Net 2 ATP per glucose if lactate is the end product
• Low endurance: only glucose used (from glycogen)
• Lactate accumulates
• High power: ATP can be produced at a high rate for a brief period.
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Aerobic vs anaerobic metabolism