How Do Organisms Supply Themselves With Energy

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Chapter 6
How Do Organisms Supply Themselves With Energy?
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Key Questions

• How do organisms supply themselves with energy?
• How do organisms extract energy from glucose?
• How is the energy in glucose used to make ATP?

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How Do Organisms Supply Themselves With Energy?

• All organisms need energy Ultimate source of
  energy is the sun
• Autotrophs make their own food examples plants,
  some bacteria
• Heterotrophs obtain chemical energy from other
  organisms
• Many proteins use ATP as a source of energy
  energy currency
• Each ATP undergoes 10,000 cycles of hydrolysis
  and resynthesis every day

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Cellular Respiration

• Process by which living cells obtain energy from
  organic molecules
• Primary aim to make ATP and NADH
• Aerobic respiration uses oxygen
• O2 consumed and CO2 released
• Organic molecules O2 ? CO2 H2O Energy
• C6H12O6 6O2 ? 6CO2 6H2O
  ATP
• Glucose Oxygen Carbon dioxide
  Water Energy

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Steps of Cellular RespirationGlucose Metabolism

• 4 metabolic pathways
• Step 1 glycolysis
• Step 2 Breakdown of pyruvate to an acetyl group
  acetyl-CoA formation
• Step 3 citric acid cycle
• Step 4 electron transport and oxidative
  phosphorylation
• Overall equation glucose oxygen ? carbon
  dioxide water ATP

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Step 1 Glycolysis

• Glycolysis can occur with or without oxygen
• Steps in glycolysis nearly identical in all
  living species
• 10 steps in 3 phases
• Energy investment steps 1-3
• Glucoses 6 carbons are split into 3-carbon
  molecules and are phosphorylated
• Uses ATP, 2 ATP hydrolyzed to create fructose-1,6
  bisphosphate
• Cleavage steps 4-5
• 6 carbon molecule broken into two 3 carbon
  molecules of glyceraldehyde-3-phosphate
• Phosphates and electrons are removed electrons
  added to NAD to make NADH produces 2 ATP
• Energy liberation Steps 6-10
• Two glyceraldehyde-3-phosphate molecules broken
  down into two pyruvate molecules producing 2 NADH
  and 4 ATP
• Breaks glucose into 2 molecules of pyruvate,
  generating 2 molecules of ATP and 2 molecules of
  NADH

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Step 1 Glycolysis
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Step 2 Acetyl CoA

• The pyruvate enters a cells mitochondria
• Breakdown of pyruvate to an acetyl group
• In eukaryotes, pyruvate in transported to the
  mitochondrial matrix
• Broken down by pyruvate dehydrogenase
• Pyruvate loses a carbon and 2 oxygens in the form
  of carbon dioxide i.e. Molecule of CO2 removed
  from each pyruvate
• Remaining acetyl group attached to CoA to make
  acetyl CoA
• 1 NADH is made for each pyruvate
• Oxygen needed for this reaction aerobic

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Step 3 Citric Acid Cycle

• Occurs in the matrix of the mitochondria
• Acetyl is removed from Acetyl CoA and attached to
  oxaloacetate to form citrate or citric acid
• 3 parts
• Part 1 6-carbon citrate and isocitrate formation
• Part 2 conversion of isocitrate into a 4-carbon
  compound
• Part 3 production of another molecule of OAA,
  which starts the cycle over again
• High energy electrons are captured in the form of
  NADH and FAD
• Series of steps releases 2CO2, 1ATP, 3NADH, and 1
  FADH2
• With each turn of the cycle, citrate loses a
  total of 8 electrons to electron acceptors such
  as NAD

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Citric Acid Cycle
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What If There Is No Oxygen?

• After glycolysis, if there is no oxygen,
  fermentation will occur
• Cells must regenerate more NAD from NADH
• Yeast form ethanol
• Animals form lactic acid (ouch)
• Catabolism breakdown of complex molecules such
  as food produces energy, involves oxidation
• Anabolism synthesis of complex molecules uses
  energy

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How Do Other Food Molecules Enter Metabolism?

• Fat, carbohydrates and proteins enter the
  cellular respiration pathway at different points
• The most likely point is at acetyl CoA

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Step 4 Electron Transport Oxidative
Phosphorylation

• The pathway of electrons from one carrier to
  another is called the electron transport chain
  each electron carrier passes its electrons to the
  next carrier
• A reduced carrier becomes oxidized when it gives
  up its electrons
• Oxygen accepts electrons

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Step 4 Electron Transport

• Group of protein complexes and small organic
  molecules embedded in the inner mitcohondrial
  membrane
• Can accept and donate electrons in a linear
  manner in a series of redox reactions
• Movement of electrons generates H
  electrochemical gradient/ proton-motive force
• Excess of positive charge outside of matrix

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Free Energy Change

• Movement from NADH to O2 is a very negative free
  energy change
• Spontaneous in forward direction
• Highly exergonic
• Some energy used to pump H across inner
  mitochondrial membrane and create H
  electrochemical gradient

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How Do Cells Harvest Energy?

• Proton gradient flow of electrons through the
  electron transport chain creates this gradient
• Chemiosmosis harnessing of the energy stored in
  the chemical gradient some machinery in the
  membrane must do this process
• Mitochondria inner and outer membrane
• Intermembrane space space between 2 membranes
• Matrix space inside the inner membrane makes
  up about 2/3 of the volume ETC is embedded in
  this inner membrane
• ETC pumps protons out of the matrix, generating
  an electrochemical gradient

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ATP Synthase

• Protein complex
• Protons flow through these channels back into the
  matrix
• Works like a turbine
• Uses energy to make ATP
• Enzyme harnesses free energy as H flow through
  membrane embedded region
• Energy conversion- H electrochemical gradient or
  proton motive force converted to chemical bond
  energy in ATP
• Racker and Stoeckenius confirmed ATP uses an H
  electrochemical gradient
• Rotary machine that makes ATP as it spins

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Summary of Energy from Glucose Oxidation