Overview cellular respiration

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Overview cellular respiration
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Catabolic Pathways

• Recall this is breaking down of complex molecules
• 2 types of pathways
• Fermentation partial pathway requires no oxygen
• Cellular respiration oxygen is consumes

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Anaerobic fermentation in yeast
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Anaerobic fermentation humans
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Cellular respiration is aerobic
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Cellular Respiration

• Cellular respiration is the process of oxidizing
  food molecules, like glucose, to carbon dioxide
  and water.
• The energy released is trapped in the form of ATP
  for use by all the energy-consuming activities of
  the cell.

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Remembering ATP

• hydrolysis of the terminal phosphate of ATP
  yields between 11 and 13 kcal/mole of usable
  energy, depending on the intracellular
  conditions.

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NAD and FAD

• 1. Each metabolic reaction in cellular
  respiration is catalyzed by its own enzyme.  2.
  As a metabolite is oxidized, NAD accepts two
  electrons and a hydrogen ion (H) results in
  NADH H. 3. Electrons received by NAD and FAD
  are high-energy electrons and are usually carried
  to the electron transport system.

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FAD and NAD
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Respiration has four distinct stages

• 1. Glycolysis
• 2. Krebs cycle
• 3. Electron transport chain
• 4. Oxidative phosphorylation

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Glycolysis

• Glycolysis is the anaerobic catabolism of
  glucose.
• It occurs in virtually all cells.
• In eukaryotes, it occurs in the cytosol.
• C6H12O6 2NAD -gt 2C3H4O3 2NADH 2H

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Glycolysis is enzyme driven

• Shockwave observe the step by step process as
  you look at your book as well as the animation.
  http//instruct1.cit.cornell.edu/courses/biomi290/
  ASM/glycolysis.dcr
• Glycolysis
• glycolysis

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Summary of yield

• The net yield from each glucose molecule is 2
  NADH, 2ATP and 2 molecules of pyruvate
• An initial investment of 2 ATP yields 4 ATP and 2
  NADH or a net gain of 2 ATP and 2 NADH

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Energy from glycolysis
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• If molecular oxygen is present the pyruvate
  enters the mitochondria

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Mitochondria

• Mitochondria are membrane-enclosed organelles
  distributed through the cytosol of most
  eukaryotic cells.
• Their main function is the conversion of the
  potential energy of food molecules into ATP.

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Mitochondria have

• an outer membrane that encloses the entire
  structure
• an inner membrane that encloses a fluid-filled
  matrix
• between the two is the intermembrane space
• the inner membrane is elaborately folded with
  shelflike cristae projecting into the matrix.
• a small number (some 510) circular molecules of
  DNA

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• Prior to entering the Krebs Cycle, pyruvate must
  be converted into acetyl CoA .
• This is achieved by removing a CO2 molecule from
  pyruvate and then removing an electron to reduce
  an NAD into NADH.
• An enzyme called coenzyme A is combined with the
  remaining acetyl to make acetyl CoA which is then
  fed into the Krebs Cycle. The steps in the Krebs
  Cycle are summarized below

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Transition of pyruvate to acetyl CoA
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• We are now back at the beginning of the Krebs
  Cycle. Because glycolysis produces two pyruvate
  molecules from one glucose, each glucose is
  processes through the kreb cycle twice.
• For each molecule of glucose, six NADH2, two
  FADH2, and two ATP.

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To review

• Krebstca

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Points to remember

• Each NADH made in the mitochondria yields 3 ATP
• NADH made in outside mitochondria yields 2 ATP
• FADH yields 2 ATP
• You will need this information as we discuss the
  electron transport chain.

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Electron transport chain overview

• Krebstca (if cant open go to bio home page at
  the bottom of page )

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Harvesting the nrg

• So far we have from glycolysis and the Krebs
  cycle (per molecule of glucose)
• ATP by substrate phosphorylation
• NADH and FADH2 (which account for most of
  the nrg stored from the metabolism of glucose )

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Electron Transport Chain

• A collection of molecules found in the inner
  mitochondrial membrane

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Key points

• Protons are translocated across the membrane,
  from the matrix to the intermembrane space
• Electrons are transported along the membrane,
  through a series of protein carriers
• Oxygen is the terminal electron acceptor,
  combining with electrons and H ions to produce
  water
• As NADH delivers more H and electrons into the
  ETS, the proton gradient increases, with H
  building up outside the inner mitochondrial
  membrane, and OH- inside the membrane.

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• http//www.wiley.com/legacy/college/boyer/04700037
  90/animations/electron_transport/electron_transpor
  t.swf
• (follow electron transport )
• respiration info (go to electron transport chain)
• Animations (should be mcgraw hill)

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Key Points to remember

• 1. NADH and FADH2 donate electrons to the series
  of electron carriers in the ETC
• The final electron acceptor is Oxygen creating
  water as a by product of cell resp.

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Points cont.

• Electron transport is coupled to ATP by
  chemiosmosis.
• Animation of Chemiosmosis during Aerobic
  Respiration

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Points cont.

• At certain steps along the chain, electron
  transfer causes electron carrying protein
  complexes to move Hydrogen ions from the matrix
  to the intermembrane space storing energy as a
  proton-motive force (hydrogen gradient)
• Animation of Chemiosmosis Proton Pumping

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Points continued

• As hydrogen diffuses back into the matrix through
  ATP synthase, its exergonic passage drives the
  endergonic phosphorylation of ADP
• Electron transport system
• (follow NADH and FADH2 as well as counting number
  of ATP made.)

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Related Metabolic Pathways

• Without oxygen electronegetive oxygen to pull the
  electrons down the transport chain, oxidative
  phosphorylation ceases.
• Fermentation provides another avenue for the
  synthesis of ATP.

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Fermentation

• 1. The oxidizing agent of glycolysis is NAD ,
  not oxygen.
• But glycolysis generates 2 ATP by oxidative
  phosphorylation.
• Fermentation regenerates ATP by transferring
  electrons are transferred to pyruvate.

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• The miracle of fermentation

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Process of alcohol fermentation

• Fermentation consists of glycolysis plus
  reduction of pyruvate to either lactate or
  alcohol and CO2.
• NADH passes its electrons to pyruvate instead of
  to an electron transport system
• NAD is then free to return and pick up more
  electrons during earlier reactions of glycolysis.

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Alcohol fermentation

• pyruvate is first decarboxylated to yield a
  2-carbon substance acetaldehyde. Acetaldehyde is
  then reduced as hydrogens are transferred from
  NADH to acetaldehyde to produce ethyl alcohol.

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lactic acid fermentation

• pyruvate is used as the direct acceptor of the
  hydrogens removed from NADH. The end product is a
  molecule of lactic acid. Lactic acid or lactate
  is a common by-product of anaerobic respiration
  in muscle cells.

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Advantage of Fermentation

• provides quick burst of ATP energy for muscular
  activity.

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Disadvantage of Ferm.

• lactate is toxic to cells. lactate changes pH
  and causes muscles to fatigue. lactate is sent to
  liver, converted into pyruvate then respired or
  converted into glucose.
• Two ATP produced per glucose molecule during
  fermentation

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Go through this site and do review questions.

• Cell Respiration Introduction
• General Human Biology