Cellular Respiration: Harvesting Chemical Energybiology- Cellular respiration in mitochondria (for cellular

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  • Cellular Respiration: Harvesting Chemical Energy

    Energy Flows through the Ecosystem

    CO2

    H2O

    Glucose

    O2

    ATP

    ECOSYSTEM

    Sunlight energy

    Photosynthesis in chloroplasts

    Cellular respiration in mitochondria

    (for cellular work)

    Heat energy

    +! +!

    Energy enters the ecosystem in form of solar energy

    Photosynthesis converts solar energy to chemical energy. Glucose and O2 are produced from CO2 and H2O Cellular respiration converts chemical energy from food to ATP. Glucose is oxidized to CO2 and H2O

    With each conversion of energy, some energy gets lost as heat

    Redox Reactions (oxidation and reduction simultaneously occur in a chemical reaction)

    The human body uses energy from ATP for all its activities

  • Cells need ATP

    !  ATP powers •  active transport •  Mechanical work (movement) •  Anabolic (endergonic) reactions

    Cellular Respiration

    Oxidative phosphorylation

    Substrate-level phosphorylation

    Substrate-level phosphorylation

    Glycolysis Glucose and other

    fuel molecules

    Pyruvate

    Pyruvate oxidation

    Acetyl-CoA

    Citric acid cycle

    Electrons carried by NADH and FADH2

    Electron transfer system and oxidative

    phosphorylation

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    Cellular Respiration occurs in three stages

    Citric acid cycle

    Glycolysis

    Pyruvate oxidation

    Oxidative phosphorylation

    ATP

    ATP

    ATP

    Cytosol

    Glucose

    2 Pyruvate

    Oxidation

    In glycolysis, glucose is oxidized to pyruvate.

    The electrons from that reaction reduce NAD+ to NADH.

    NADH carries the electrons to be used in the oxidative phosphorylation

  • In Glycolysis and the Citric Acid Cycle, ATP is produced by Substrate Level Phosphorylation

    Enzyme

    ADP

    P Substrate

    Product

    Enzyme

    ATP +

    Substrate

    Product

    The Electron Carrier NAD+ can pick up 2 electrons

    Pyruvate is transported into the mitochondrial matrix as Acetyl-CoA

    Acetyl CoA (acetyl coenzyme A)

    Coenzyme A

    Pyruvate

    CO2

    NAD+ NADH H+

    CoA

    +

    Glycolysis

  • NADH must be recycled

    !  For glycolysis to continue, NADH must be recycled to NAD+ by either:

    1. Aerobic respiration •  Oxygen is available as the final electron

    acceptor •  Produces significant amount of ATP

    2. Fermentation •  Occurs when oxygen is not available •  Organic molecule is the final electron acceptor

    Summary Glycolysis

    !  Converts 1 glucose (6 carbons) to 2 pyruvate (3 carbons)

    !  10-step biochemical pathway !  Occurs in the cytoplasm !  Net production of 2 ATP molecules by substrate-

    level phosphorylation !  2 NADH produced by the reduction of NAD+

    The Pyruvate needs “grooming” for the next step

    Citric acid cycle

    Glycolysis

    Pyruvate oxidation

    Oxidative phosphorylation

    Mitochondrial matrix

    Pyruvate is transported into the mitochondrial matrix as Acetyl-CoA

    Pyruvate

    Acetyl-CoA

  • Mitochondria, Sites of Cellular Respiration Acetyl-CoA

    Summary of Krebs Cycle (Citric Acid Cycle) Reactions

    !  For each Acetyl-CoA entering the Krebs Cycle: •  2 molecules of CO2 are released

    •  3 NAD+ are reduced to 3 NADH

    •  1 FAD (electron carrier) is reduced to FADH2 •  •  1 ATP is produced

    •  The initial acceptor molecule Oxaloacetate is regenerated

  • Pyruvate

    Acetyl-CoA

    Citric acid cycle

    The last step of Cellular Respiration: Oxidative Phosphorylation

    Citric acid cycle

    Glycolysis

    Pyruvate oxidation

    Oxidative phosphorylation

    Inner mitochondrial membrane

    Oxidative Phosporylation consists of the Electron transport chain and Chemiosmosis

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    Electron Transport Chain

    !  ETC is a series of membrane-bound electron carriers

    !  Embedded in the inner mitochondrial membrane !  Electrons from NADH and FADH2 are transferred

    to complexes of the ETC !  Each complex •  A proton pump creating proton gradient •  Transfers electrons to next carrier

  • Why Electron Transport?

    2 H+ + 2 e–

    2 H

    (from food via NADH)

    Controlled release of energy for

    synthesis of ATP

    ATP

    ATP

    ATP

    2 H+

    2 e–

    H2O

    + 1/2 O2

    1/2 O2

    Cellular respiration

    Fr ee

    e ne

    rg y,

    G Electron transport chain

    1/2 O2 H2 +

    H2O

    Explosive release of

    heat and light energy

    Uncontrolled reaction

    Fr ee

    e ne

    rg y,

    G

    H2 + ! O2 2 H + ! O2

    2 H+

    2 e!

    2 e! 2 H+ +

    H2O

    ! O2

    Controlled release of

    energy

    Electron transport

    chain

    ATP

    ATP

    ATP Explosive

    release

    Cellular respiration Uncontrolled reaction (a) (b)

    Fr ee

    e ne

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    G

    Fr ee

    e ne

    rg y,

    G

    H2O

    Chemiosmosis

    !  Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion

    !  Membrane relatively impermeable to ions !  Most protons can only reenter matrix through

    ATP synthase •  Uses energy of gradient to make ATP from ADP +

    Pi

    Overview Cellular Respiration Inhibitors of the Electron Transport Chain

    H+

    H+

    H+

    H+

    H+

    H+ H+ H+ H +

    H+

    H+

    H+ H+

    O2

    H2O P ATP

    NADH NAD+

    FADH2 FAD

    ATP Synthase

    +! 2

    ADP +!

    Electron Transport Chain Chemiosmosis

    1 2

    Rotenone Cyanide, carbon monoxide

    Oligomycin

    DNP

  • Summary: Glycolysis, Citric Acid Cycle and Oxidative Phosphorylation

    CYTOSOL Electron shuttles span membrane 2 NADH

    or

    2 FADH2

    MITOCHONDRION

    Oxidative phosphorylation: electron transport

    and chemiosmosis

    2 FADH2 2 NADH 6 NADH

    Citric acid

    cycle

    2 Acetyl CoA

    2 NADH

    Glycolysis

    Glucose 2

    Pyruvate

    + 2 ATP

    by substrate-level phosphorylation

    + 2 ATP

    by substrate-level phosphorylation

    + about 32 or 34 ATP

    by oxidation phosphorylation, depending on which shuttle transports electrons form NADH in cytosol

    About 36 or 38 ATP Maximum per glucose:

    The actual yield is about 30 ATP per molecule of glucose due to leaky membranes

    The Fate of Pyruvate is Dependent on Oxygen Availability

    Fermentation occurs when oxygen is not available

    Glucose

    Pyruvate

    Glycolysis

    Lactate

    Alcoholic Fermentation

    Glucose

    Pyruvate

    Glycolysis

    Ethanol

    Fermentation replenishes NAD+ to further drive Glycolysis

  • Cells use many kinds of organic molecules as fuel for cellular respiration (catabolic processes)

    OXIDATIVE PHOSPHORYLATION

    (Electron Transport and Chemiosmosis)

    Food, such as peanuts

    Carbohydrates Fats Proteins

    Sugars Glycerol Fatty acids Amino acids

    Amino groups

    Glucose G3P Pyruvate Acetyl CoA

    CITRIC ACID

    CYCLE

    ATP

    GLYCOLYSIS

    Food molecules provide raw materials for biosynthesis (anabolic processes)

    ATP needed to drive biosynthesis

    ATP

    CITRIC ACID

    CYCLE

    GLUCOSE SYNTHESIS

    Acetyl CoA

    Pyruvate G3P Glucose

    Amino groups

    Amino acids Fatty acids

    Glycerol Sugars

    Carbohydrates Fats Proteins

    Cells, tissues, organisms

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