Energy Releasing Pathways: Cellular Respiration and Glycolysis

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Energy Releasing PathwaysCellular Respiration
and Glycolysis

• Biology 1010 -Chapter 8

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Introduction

• A. Unity of Life
• 1. all organisms use energy
• 2. byproducts of metabolism
• a. carbon dioxide
• b. water
• c. heat
• 3. at the biochemical level, all life is united

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Process of ATP Synthesis

• A. Comparison of Pathways
• 1. ATP is the energy currency of all cells
• 2. glycolysis
• a. common to all pathways
• b. splitting of glucose forms ATP
• c. occurs in the cytoplasm of the cell

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• 2. Fermentation and anaerobic electron
  transport
• a. occur in the absence of oxygen
• b. release small amounts of ATP
• 3. Aerobic respiration
• a. main pathway for converting CHO to ATP
• b. occurs in the mitochondria
• c. requires oxygen
• d. efficient

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• 4. chemical formula
• H2O C6H12O6 O2 CO2 H2O
• 5. similarities to photosynthesis

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Glycolysis

• A. First stage of all energy-releasing pathways
• 1. occurs in the cytoplasm of the cell
• 2. does not require oxygen
• 3. evolutionary considerations

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• B. Stages
• 1. energy investment phase
• a. glucose is phosphorylated by 2 ATP
  molecules
• 2. energy releasing phase
• a. glucose is split to form 4 ATP and 2
  pyruvate molecules.
• b. electrons captured by NAD to form NADH
  (to ETS)
• c. ATP is produced by substrate- level
  phosphorylation.

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C. Inputs and Outputs

• 1. Inputs
• a. glucose
• b. NAD
• c. ADP

• 2. Outputs
• a. 2 pyruvate
• b. 2 NADH
• c. 2 ATP (net)

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Krebs Cycle Aerobic Respiration

• A. General
• 1. occurs in the mitochondria (inner membrane
  space)
• 2. requires oxygen
• 3. input is the pyruvate (3-C)from glycolysis,
  which is modified to form acetyl-CoA
• 4. carbon leaves the cycle as CO2

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• B. Stages
• 1. pyruvate is converted to acetyl-CoA
• 2. oxygen is used to break C-C bonds
• 3. broken bonds release energy and
  electrons.
• 4. energy is used to form ATP by oxidative
  phosphorylation
• 5. electrons captured by NAD and FAD to
  form NADH and FADH2 (to ETS)

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• 6. carbon leaves as CO2
• 7. cyclic pathway - intermediates are
  recycled
• 8. 1 glucose 2 pyruvate. Two complete turns
  of the pathway per glucose molecule
• 9. 2 ATP produced per glucose

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C. Inputs and Outputs

• 1. Inputs
• a. pyruvate
• b. NAD and FAD
• c. ADP
• d. O2

• 2. Outputs (per glucose)
• a. CO2
• b. NADH and FADH2
• c. 2 ATP

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Electron Transport System (ETS)

• A. General
• 1. inputs are the NADH and FADH2 from glycolysis
  and the Krebs cycle
• a. processes electrons, not carbon
• 2. located on the inner membrane of the
  mitochondria (integral proteins)
• 3. uses oxygen as a terminal electron receptor

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• 4. ATP is produced by chemiosmosis or
  electron-level phosphorylation
• B. Stages of chemiosmosis
• 1. NADH and FADH2 transfer electrons to integral
  proteins on the inner membrane
• a. electrons are high energy
• 2. passage of energy between proteins pumps H
  ions out of the inner space
• a. generates an electrical gradient

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• 3. channels are opened, allowing the H ions
  to reenter, generating ATP.
• 4. oxygen is used to gather the spent
  electrons, generating water
• 5. high amounts of ATP are produced,
  typically 32 ATP per glucose.
• 6. NAD and FAD are recycled

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C. Inputs and Outputs

• 1. Inputs
• a NADH and FADH2
• b. ADP
• c. O2

• 2. Outputs (per glucose)
• a. H2O
• b. NAD and FAD
• c. 32 ATP

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Summary of Energy Harvest

• A. ATP per glucose
• 1. glycolysis 2 ATP
• 2. Krebs 2 ATP
• 3. ETS 32 ATP
• B. Variations
• 1. yield per glucose may be 32-38 ATP depending
  on cell type

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Anaerobic Respiration

• A. General
• 1. occur in the absence of oxygen or oxygen-poor
  environments
• 2. after glycolysis, pyruvate is converted to
  other molecules than acetyl-CoA.
• 3. many bacteria are completely anaerobic

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• B. Fermentation Pathways
• 1. Lactate fermentation
• a. pyruvate is converted to lactate
• b. process regenerates NAD
• c. occurs in bacteria and muscle cells
• 2. Alcohol fermentation
• a. pyruvate is converted to acetaldehyde
  and then alcohol
• b. NAD is regenerated

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• C. Anaerobic electron transport
• 1. some bacteria have modified electron
  transport systems.
• 2. types
• a. convert SO4 to H2S
• b. convert NO3 to NO2
• 3. evolutionary significance