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The ETC

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Goal is to make A LOT of ATP

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REDOX

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REDOX with coenzyme

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NADH + H and FADH2

  • NADH + H and FADH2 are reduced forms of coenzymes

    • NAD+ (ox) + 2H + 2e- --> NADH + H (red)

      • derived from niacin (vitamin B3)​

    • FAD (ox) + 2H + 2e- --> FADH2 (red)

    • derived from riboflavin (vitamin B2)

  • NADH + H and FADH2 are generated in glycolysis, fatty acid oxidation, the Krebs cycle, etc

    • much of the oxidation of nutrients involves removing H+ and e- from glucose, FA and AAs​

    • The H+ and e- are given to NAD+ and FAD and they are reduced

    • they are the major carriers of energy released from the oxidation of glucose and other energy nutrients

REDOX of NADH

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ETC

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Where the complexes are

Where protons are pumped into

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NADH + H and FADH2 carry H+ and e- to the ETC at different sites

  • protons (H+) are translocated into the inter membrane space

  • electrons travel down a series of complexes that are reduced and oxidized

    • along the way, energy is released

    • each component is increasingly electronegative

    • as the energetic electron passes from one to another, the energy is harnessed

    • the harnessing of energy is what allows H+ to move across into the space between the mitochondrial membranes

  • Ultimately water is produced when electrons are passed to oxygen gas

    • O2 is the final e- acceptor​

  • since oxygen is the final electron acceptor, this process is called aerobic respiration

    • this is the only place we see O2 in energy metabolism​

  • the difference in H+ concentration across the membrane establishes an electro-chemical gradient

    • also called proton gradient ​

    • creates a strong proton motive force toward the matrix (lots of energy involved)

Oxidative Phosphorylation

  • The overall movement of e- through the increasingly electronegative complexes and the movement of H+ to the other side causes energy to be released

  • the energy released is used to drive the synthesis of ATP​

  • the H+ move back across the membrane through and enzyme complex called ATP synthase

    • this movement provides the energy for the synthesis of ATP from ADP and phosphate

  • The use of the proton gradient to drive ATP synthase is known as the chemiosmotic theory

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ETC complexes

  • The complexes that make up the ETS are made up of enzymes

    • Some are heme proteins - contain Fe​

      • the most important heme proteins​

    • some also contain Cu

    • Fe and Cu are both transition metals

      • Fe++ <---> Fe+++​

      • Cu+ <---> Cu++

    • their ability to accept/donate e- makes them good candidates for ETC

Shuttle Systems

  • reducing equivalents generated in the TCA are in the mitochondria 

  • reducing equivalents generated in glycolysis are in cytoplasm

    • need to be transported across mitochondrial membrane​

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  • more active

  • malate is permeable to the inner membrane

  • the recipient of the reducing equivalent inside mitochondria is NAD+

    • NADH + H to ETC -> 3 ATP

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  • less active

  • the recipient of the reducing equivalent inside mitochondria is FAD

    • FADH2 to ETC -> 2 ATP

ATP Production

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Total ATP from Glucose

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Summary of Cellular Respiration

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©2023 by Syracuse University Dr.Margaret Voss

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