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ELECTRON TRANSPORT CHAIN
Stage 4:
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How far have we come?
• We began with our simple glucose molecule• Through the processes of...– GLYCOLYSIS– PYRUVATE OXIDATION– KREBS CYCLE
...we have used the energy stored in the C-C bonds of glucose to help ATP
• Directly (substrate-level phosphorylation)• Indirectly (oxidative phosphorylation)
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Energy Totals • GLYCOLYSIS
• PYRUVATE OXIDATION
• KREBS CYCLE
ATP USED ATP produced
NADH produced
FADH2
produced
2 6 10 2
ATP USED ATP produced
NADH produced
FADH2
produced
2 4 4 0
ATP USED
ATP produced
NADH produced
FADH2
produced
2 4 2 0
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So what’s the deal with ATP??
• C6H12O6 + 6O2 6CO2 + 6H2O + 36 ATP
• We need to produce 36 ATP in Cell. Resp.• After 3 stages, we have only produced 6 ATP
through substrate-level oxidation• Thus, there are 30 ATP left to create– We produce the remaining 30 ATP through
oxidative phosphorylation in the ETC
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ELECTRON-TRANSPORT-CHAIN
• In this step, we will utilize the energy provided by the electron carriers NADH and FADH2
•Extremely EXERGONIC∆G = -2870 kJ/Mol
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How it works• NADH + FADH2 eventually transfer the electrons they carry to a
series of proteins that are located in the inner membrane
• The components of the ETCare arranged in order of increasing electronegativity
• Thus, allowing the electrons toflow, or BE TRANSPORTED, between the compounds
• Every step involves oxidationand reduction rxns.
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How it works• Every time an electron moves from one molecule to the next,
free energy is released
• The free energy is used to pump H+ ions, or PROTONS, from the mitochondrial matrix into theINTERMEMBRANE SPACE
• The ETC needs a highly electronegative compound to oxidize the last protein– OXYGEN is used here, as it is one
of the most electronegative compounds on earth
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How it works• An oxygen atom removes two é from the final protein complex • Oxygen then combines with 2 protons (H+) in the mitochondrial
matrix to form an H2O molecule
Diagram• The red path shows the path
that é travel through the ETC• KNOW NAMES OF THESE
MOLECULES
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How it works
NADH DEHYDROGENASE
CYTOCHROME b-c1 COMPLEX
CYTOCHROME OXIDASE COMPLEX
UBIQUINONE (Q) cytochrome C
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NADH + FADH2... Not so similar• NADH passes its electrons to the first protein complex
– NADH DEHYDROGENASE
• FADH2 passes its electrons to Q (or ubiquinone)
• This distinction means that:– NADH = 3 H+ pumped out– FADH2 = 2 H+ pumped out
• SO...
– NADH produces 3 ATP– FADH2 produces 2 ATP
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NADH + FADH2... Not so similar• The NADH you produced in glycolysis works differently than the
NADH produced in pyruvate oxidation and Krebs cycle– Why?
• Glycolysis occurs in the cytoplasm, thus NADH has to travel through the double membrane of mitochondria– it can’t pass the inner membrane
• NADH passes its é through a protein transport to FAD thus forming FADH2
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ATP PRODUCTION• Electrochemical Gradient: A concentration gradient created by
pumping ions into a space surrounded by a membrane that is impermeable to the ions– This is exactly what we are doing when we pump H+ ions into the
intermembrane space using the ETC– Thus, the inner membrane becomes a H+ reservoir – An potential difference, or VOLTAGE, is created across the
membrane• +ve charge in the intermembrane space • –ve charge in the mitochondria matrix +
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ATP PRODUCTION• H+ ions can not diffuse back through the innermembrane • They need to be pumped back by the transport protein
ATP SYNTHASE• As H+ ions are passed through
ATP SYNTHASE, the free energy of the gradient is reduced, thus releasing enough energy to produce ATP
• ADP + Pi ATP
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ATP PRODUCTION• This process was coined: CHEMIOSMOSIS• ATP synthesized was caused by the ‘osmosis of H+ ions’
• Chemiosmosis is said to be COUPLED to the ETC
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Final Energy Tally
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Theoretical Yield vs. Actual Yield
• It is possible that we will not always obtain 36 ATP for every glucose molecule that we used
• 2 reasons:1. Some H+ ions may make it through the inner mitochondrial
membrane reducing the number of H+ ions that pass through ATP synthase.
2. Some of the protons in the H+ reservoir might get used up in other cellular reactions