BIOL 110 Chapter Notes - Chapter 28: Electron Transport Chain, Acetyl-Coa, Electron Acceptor
Tutorial 28
Sunday, November 20, 2016
12:04 PM
Energy III - Cellular Respiration (Krebs Cycle and Electron Transport Chain)
• The krebs cycle
o Complete oxidation of glucose results in the release of 684 kcal of energy
o In eukaryotes, pyruvate is transported across the mitochondrial membrane and then
converted to acetyl CoA
• Production of NADH and CO2
• Acetyl CoA is oxidized during the krebs cycle
o During krebs cycle, electrons are removed from acetyl CoA and those electrons reduce more
NAD+, with FAD
o ATP is generated via substrate level phosphorylation
o Complete oxidation of acetyl CoA
o CO2 released as a byproduct, electron carriers are reduced to form NADH and FADH2
• The role of NADH and FADH2
o Glucose catabolism ends during the krebs cycle
o Only one additional ATP molecule is produced by substrate level phosphorylation during the
krebs cycle
o The balance of extracted energy is in NADH and FADH2
o In the next phase of cell respiration NADH and FADH2 are passed to membrane-bound
enzymes in the mitochondrion, the electron transport chain
• Electrons provide energy to do work
▪ Movement of positively charged hydrogen atoms (H+) - protons
o Movement of protons across the inner mitochondrial membrane creates a voltage/charge
differential that will be used to synthesize ATP
• The electron transport chain
o NADH and FADH2 convey their electrons to the electron transport chain
o Transport chain is composed of molecules on the inner membrane of the mitochondria
• Each membrane protein has a specific electronegativity
• More electronegative = more energy required too keep the electron away from it
• a slightly electronegative membrane protein will pull electrons away from reduced
electron carriers.
o Electrons reduce oxygen, add hydrogen ions, water is produced as a waste product
o Each step has a -ΔG. , the electron decreases in energy, and more energy is made available
to do work (work involves the movement of protons)
o Oxygen acts as the terminal electron acceptor
• Maximal amount of free energy is released, more protons can be transported, greater
charge buildup occurs across the inner mitochondria membrane
• Chemiosmosis
o Protons accumulate on the inside of the inner mitochondrial membrane
o Voltage across the membrane; this stored energy is used to synthesize ATP
o Protons from intermembrane space move back into the mitochondrial matrix
• ADP is phosphorylated to ATP (chemiosmosis)
o Chemiosmosis- accomplished in the presence of the protein complex ATP synthase, in the
inner mitochondrial membrane
• Oxidative Phosphorylation and ATP yield
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