Electron Transport Chain Takes place in the cristae of mitochondrium  Electron acceptors are embedded in the cristae Begins with electron from NADH  Reduces flavoprotein  Electron is passed to other molecules that have higher electronegativity Reduces new acceptor and donor is oxidated Electron ultimately is accepted by O 2 molecule  Very high electronegativity  For every 2 NADH molecules O 2 is reduce to 2H 2 O

Electron Transport 2 Each new acceptor requires that the electron be at a slightly lower energy state Energy is siphoned off of the electrons in small increments The energy is used by the acceptor molecules to change conformation All are proteins except Q (ubiquinone) is lipid

Close-up of Cristae Many electron acceptors used released energy to pump an H+ proton into the intermembrane space  Gradient of H+ is formed outside of cristaes

Fig Protein complex of electron carriers H+H+ H+H+ H+H+ Cyt c Q    VV FADH 2 FAD NAD + NADH (carrying electrons from food) Electron transport chain 2 H / 2 O 2 H2OH2O ADP + P i Chemiosmosis Oxidative phosphorylation H+H+ H+H+ ATP synthase ATP 21

Oxidative phosphorylation ATP is actually synthesized by enzyme ATP synthase  Many copies embedded in cristae Hydrogen gradient needs to reach equilibrium  H+ can only pass through ATP synthase molecule Passage of H+ turns molecule like a water wheel ATP is generated by enzyme action

Fig INTERMEMBRANE SPACE Rotor H+H+ Stator Internal rod Cata- lytic knob ADP + P ATP i MITOCHONDRIAL MATRIX

Net ATP Production Glycolysis 2 ATP, Krebs 2 ATP, Electron Transport & oxidative phosphorylation 34 ATP Total of 38 ATP/glucose

Fermentation Used when oxygen is not available as electron acceptor Not as efficient as oxidative phosph.  In humans, only 2 ATP are produced by fermentation Accumulation of waste molecules  Sometimes can be used later as energy source Type of fermentation is known by waste product

Types of Fermentation Alcohol fermentation  Results in ethanol production  Performed by bacteria and fungi Lactic acid fermentation  Used by animals  Results in lactate formation  Causes muscles to ache after workout  Anaerobic conditions

Fig ADP + 2PiPi 2 ATP Glucose Glycolysis 2 NAD + 2 NADH 2 Pyruvate + 2 H + 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 PiPi 2 ATP GlucoseGlycolysis 2 NAD + 2 NADH + 2 H + 2 Pyruvate 2 Lactate (b) Lactic acid fermentation 2 CO 2

Why Fermentation Pyruvate is dividing point of two systems If O 2 is available pyruvate enters mitochondrium If O 2 level is low Pyruvate stays in cytosol and undergoes fermentation

Macromolecules and Respiration Many types of macromolecules can be used as a source for respiration  Fats and proteins are important They enter pathway at various point

Regulation of Respiration Very complex regulation Feedback inhibition of ATP or Citrate can stop early stages of reactions Allows cell to produce ATP when needed