• Clinical science

Mitochondrial respiratory chain

Overview

Electron transport chain and ATP synthesis

Electron transport chain

Complex I (NADH dehydrogenase)

  • Transfers two protons (H+) and two electrons (e-) to coenzyme Q
  • NADH NAD+ + H+ + 2 e-
  • Pumps four protons into the intermembrane space

Complex II (contains succinate dehydrogenase )

  • Transfers two protons (H+) and two electrons (e-) to coenzyme Q
  • FADH2 FAD + 2 H+ + 2 e-
  • Does not pump protons into the intermembrane space

Complex III (coenzyme Q)

  • Transfers two electrons (e-) from coenzyme Q to two molecules cytochrome c
  • Reduced coenzyme Q (QH2) + 2 H+ + 2 oxidized cytochrome c → oxidized coenzyme Q + 4 H+ + 2 reduced cytochrome c
  • Pumps two protons (H+) into the intermembrane space
  • Two protons are released into the intermembrane space by coenzyme Q

Complex IV (cytochrome c oxidase)

  • Reduces oxygen (O2) to water (H2O) via cytochrome a/a3 (Cu/heme protein)
  • 2 reduced cytochrome c + ½ O2 + 4 H+ 2 oxidized cytochrome c + H2O + 2 H+
  • Pumps two protons (H+) into the intermembrane space

Oxidative phosphorylation

Complex V (ATP synthase)

  • ADP + PiATP
  • Acts as proton channel, works like a turbine → flow of protons allows generation of ATP
  • For every 4 protons one ATP is generated
  • Yield
    • 1 NADH transport of 10 H+ 2.5 ATP
    • 1 FADH2 transport of 6 H+ 1.5 ATP

Clinical significance

  • Kaplan. USMLE Step 1 Lecture Notes 2018: Biochemistry and Medical Genetics. New York, NY: Kaplan; 2017.
  • Chatterjea M, Shinde R. Textbook of Medical Biochemistry. New Delhi, India: JP Medical Ltd; 2011.
last updated 08/08/2018
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