Cellular Respiration C6H12O6 602 6CO2 6H2O

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Cellular RespirationC6H12O6 602 ? 6CO2 6H2O
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Oxidation-reduction

• Oxidation-reduction LEO the lion goes GER.
• The electrons are frequently accompanied by a
  hydrogen proton.

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• Since electrons represent energy, oxidation
  involves the release of energy
• Reduction stores energy in the atom or molecule.
• Whenever one substance is oxidized, another
  substance is reduced.
• Oxidation-reduction reactions transfer energy
  within living organisms.

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ATP

• ATP ATP is the universal energy currency of all
  cells.
• High-energy covalent bonds link the three
  phosphate groups.
• When one of those bonds is broken, ADP and an
  inorganic phosphate are left, and 7.3 kcal/mole
  of energy are released.

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• This is enough energy to drive endergonic
  reactions in the cell or perform other work.
• ATP is constantly being synthesized and broken
  down in living cells
• It cycles and recycles between ADP Pi and ATP.
• The energy required to synthesize ATP from ADP
  Pi comes from photosynthesis or cellular
  respiration.

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Structure of ATP

• Ribose sugar bound to adenine base and chain of
  three phosphate groups
• Linked phosphates store energy of their
  electrostatic repulsion
• Phosphate transfer (phosphorylation) charges that
  molecule

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Step Wise Chemical Pathways

• The oxidation of glucose is a step wise reaction.
  Complete oxidation occurs in 3 pathways
  glycolysis, Krebs cycle, and the electron
  transport chain.
• NAD and FAD serve as electron carriers, and are
  reduced and then later oxidized to keep the
  reaction going.

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NAD and FAD

• FADflavin adenine dinucleotide NAD
  Nicotinamide adenine dinucleotide
• (N 1 and 5 carry H to make FADH2 )

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ALL CELLS perform Glycolysis

• Takes place in the CYTOPLASM
• It produces 4 ATP costs 2 ATP to get started, so
  it nets 2 ATP for the cell
• 10 enzyme-catalyzed steps
• First 5 devoted to splitting 6-C glucose into TWO
  3-C G3P

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Glycolysis

• Does NOT require oxygen
• Its end-product is pyruvate
• With oxygen present aerobic the pyruvate is
  modified and goes into the Krebs Cycle aka
  Citric Acid Cycle or TCA IF MITOCHONDRIA ARE
  PRESENT!!

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GLYCOLYSIS

• WITHOUT oxygen present anaerobic
• In organisms like yeast, fermentation takes place
  and the end-product is ethanol
• In organisms like us, deep in muscle tissue,
  anaerobic respiration takes place as well, but
  the end-product is lactic acid!
• This causes muscle cramps once youve used up
  your oxygen supply in the tissues!

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GLYCOLYSIS

• Energy from glucose extracted in 10 steps
• Produces ATP by substrate level phosphorylation
• Only 3.5 efficientmost of the energy is still
  tied up in the end-product, pyruvate

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Glycolysis

• Glucose priming
• Change glucose into a compound that is readily
  cleaved in half
• Uses TWO ATP
• Cleavage and Rearrangement
• One molecule is G3P, the other must become G3P

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Glycolysis

• Substrate-Level Phosphorylation and oxyidation.
• Thats what we call the remaining 5 reactions.
• Oxidation
• TWO e- and one proton H transferred from G3P
  to NAD
• Forms NADH
• One per G3P, thus 2 per glucose since this is
  happening twice!

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Glycolysis

• ATP generation by substrate level
  phosphorlyation.
• G3P is converted into pyruvate 2/glucose
• TWO ATP are made per G3P 4/glucose
• Tally 2 ATP net, 2 NADH important later, 2
  pyruvate still house an awful lot of energy!if
  you have mitochondria, you can harvest more
  energy from pyruvate

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Net Energy

• 24 kcal/ mole of glucose
• Puny but true. Life on this planet survived
  about a billion years on just glycolysis

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Recap

• All cells use glycolysisno O2 required
• Among first to evolve
• Occurs in cytoplasm
• Glucose ? 2 pyruvate
• 2 ADP ? 2 ATP
• 2 NAD ? 2 NADH

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Recycling NAD

• Cell will accumulate NADH and run out of NAD
• Two ways to recycle
• FERMENTATION anaerobic
• RESPIRATION aerobic

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Aerobic Respiration

• Oxygen is the final electron acceptor
• Water is the final product
• Cell must have mitochondria
• Pyruvate ? acetyl- CoA? Krebs cycle? ETS

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Fermentation

• Organic molecules serve as final electron
  acceptor
• Occurs in many organisms EVEN THOSE CAPABLE OF
  AEROBIC RESPIRATIONlike you!
• Reduces all or part of the pyruvate
• Ethanol lactic acid are the most common end
  products.

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Aerobic Respiration

• Eukaryotes? occurs ONLY in mitochondria
• In prokaryotes it occurs along the plasma
  membrane
• Pyruvate is oxidized ?acetyl-CoA
• Oxidation of acetyl-CoA takes place in the Krebs
  cycle

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Producing Acetyl-CoA

• One C is cleaved from 3-C pyruvate and LEAVES AS
  CO2
• Decarboxylation reaction
• The 2-C fragment is an acetyl group
• A PAIR of e- and an associated H reduces NAD to
  NADH

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USING ACETYL-CoA

• If it is NOT stored then it enters the Krebs
  Cycle
• Nine reactions in 2 stages
• Priming
• Acetyl CoA first joins the cycle
• Chemical groups are rearranged isomerization
  step

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• Energy Extraction is stage 2
• Four of the six reactions are oxidations,
  electrons are removed and electron carriers
  become VERY important in the production of ATP
• One reaction generates an ATP via substrate level
  phosphorylation

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Reaction 1A condensation rxn.

• 2-C acetyl-CoA 4-C oxaloacetate ? 6-C
  citrate CoA which can be used over and over!
• Irreversible
• Inhibited by large amounts of ATP already present

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Reaction 2 3--Isomerization

• Hydroxyl group repositioned
• Water removed from one C and then added to a
  different C
• RESULT a change in position of an H and OH
• Molecule is now ISOCITRATE

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Reaction 4the first oxidation

• Isocitrate undergoes oxidative decarboxylationfan
  cy for chopping off a carbon and losing a pair of
  e-s in the process
• The pair of e- reduce NAD to NADH
• The chopped off C becomes CO2
• Now we have a 5-C a-KETOGLUTARATE

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Reaction 5the second oxidation

• The 5-C a-KETOGLUTARATE is decarboxylated
• The 4-C fragment that is left is called a
  Succinyl group CoA ? succinyl CoA
• 2 more e- reduce another NAD to NADH
• The second CO2 is released

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Reaction 6Substrate-level phosphorylation

• The bond between the succinyl group and CoA is
  high energy
• GDP Pi ? GTP just substitute guanine for
  adenine in A TP
• GTP? ATP
• Remaining 4-C molecule is SUCCINATE

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Reaction 7The third oxidation

• Succinate oxidized to fumarate
• Not enough ?G for the NAD reaction so FAD
  FOUR e- and TWO H ? FADH2
• FADH2 can contribute e- to ETS

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Reactions 8 9Regeneration of OXALOACETATE

• Water is added to 4-C FUMARATE forms 4-C MALATE
• Malate oxidized to 4-C OXALOACETATE and 2 e- are
  released
• NAD the 2 e- ? NADH
• Ready to start again!

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Summary So Far
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ETS or ETCHarvesting e- in stages

• Theres thousands of KJ of energy stored in the
  gas tank of a car
• If you release it all at once, most is wasted
• Cells are no different
• NADH contains 2 e- H
• If all the energy is released at once, most is
  wasted
• Better to release in stages? ETS

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Following the Electrons

• 2 e- pass along the ETS in the presence of
  oxygen
• Structure of ETS
• Series of proteins embedded in INNER MEMBRANES OF
  MITOCHONDRIA cristae
• e- delivered BY NADH to top of chain
• e- captured by oxygen at the bottom, thus E is
  released in stages

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The proteins embedded

• NADH carries its 2 e- to NADH hydrogenase
• Ubiquinone carries e- to the cytochromes
• This complex of cytochromes acts as a proton
  pumpdrives protons outside of membrane

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ETS Proteins continued

• Cytochrome c carries e- to cytochrome oxidase
  complex
• 4 e- are used to reduce one oxygen molecule
• This oxygen molecule combines with 4 H to form
  water

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Differences between NADH FADH2

• NADH carries e- to the FIRST position in chain
  AND has higher energy e- s
• FADH2 caries e- later down the chain and carries
  lower energy e- s

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Building an Electrochemical Gradient

• ETS transports e- along the chain
• E transports H to outer compartmentintermembrane
  space
• Transport accomplished by proton pumps,
  transmembrane proteins
• NADH activates 3 pumps
• FADH2 activates 2 pumps
• STILL NO ATP!!!

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CHEMIOSMOSISmanufacturing ATP

• Concentration of protons H in outer
  compartment increases over inner compartment
  matrix
• H attracted back inward through ATP synthase
• ATP is synthesized when protons diffuse through
  them this is chemiosmosis, and makes ATP by
  oxidative phosphorlyation.
• ATP leaves the mitochondrion by facilitated
  diffusion

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ATP Synthase Animation

• http//www.labaction.com/view_video.php?viewkey75
  e45bba028a21ed3804

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Theoretical ATP Yield

• Since NADH activates 3 pumps, expect 3 ATP 10
  NADH 30 ATP
• Since FADH2 activates 2 pumps, expect 2 ATP 2
  FADH2 4 ATP
• NADH transport from glycolysis costs 1 ATP4 were
  made, so really costs 2 ATP leaving 2 ATP
• GRAND TOTAL 36 ATP expected

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ACTUAL YIELD

• Must obey the First Law of Thermodynamics so the
  net is closer to 30 ATP in eukaryotes
• Inner membrane is leaky, so some H sneak in
  without producing ATP
• Mitochondria use proton gradient for other
  purposes
• 2.5 ATP/NADH 1.5 ATP/FADH2 is more realistic

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Regulating ATP production

• If ATP is high, glycolysis, Krebs and fatty acid
  breakdown is inhibited. This is an example of
  feedback inhibition
• When ATP is low, ADP is high which activates
  enzymes of carbohydrate catabolism
• If NADH levels are high, no decarboxylation of
  pyruvate to get Krebs startedNADH inhibits enzyme

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You cannot live on sugar glucose
alone! --your Mom

• Proteins
• Break into AAs
• Deaminate
• Alanine to pyruvate
• Glutamate to a ketoglutarate
• Aspartate to oxaloacetate
• AAs join the Krebs cycle at different points

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• FATS
• Degrade into individual fatty acids glycerol
• Oxidized in matrixenzymes attack long fatty acid
  chains and remove 2C chunks
• Entire chain is converted into acetyl-CoA
• Called Beta oxidation
• Glycerol is converted into pyruvate.

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Biosynthesis

• When there is an excess of intermediates they can
  be used to build necessary molecules.
• Lipids can be generated from excess acetyl CoA
• Glycogen is generated from excess pyruvate
• Amino acids are genertated from different stages
  of the krebs cycle.

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Metabolism Summary