Biochemistry

Chemiosmosis

Anisha ValliLeave a comment

INNER MITOCHONDRIAL MEMBRANE

  • Contains the ETC, ATP synthase, ADP-ATP transporter, phosphate translocase and more
  • Impermeable to small molecules (H+, ATP, ADP & Pi)
  • ETC pumps protons across impermeable inner membrane: generates chemiosmotic gradient (proton-motive force)

ATP SYNTHASE STRUCTURE

F0 (c, gamma, and epsilon subunits)

  • Cylindrical structure embedded in membrane
  • Channel through which H+ flows down gradient

F1 (alpha and beta subunits)

  • Sits on top of F0 on matrix side

Stator (a, b, and delta subunits)

  • Prevents F1 from rotating as F0 does

ATP SYNTHESIS

  1. H+ from intermembrane space enters F0
  2. H+ protonates asparagine residue within channel
  3. Induces rotation of c-ring
  • Electrochemical energy (H+ gradient) converted to mechanical energy (rotation)
  • On the matrix side, ADP & Pi bind F1 beta subunit
  1. Beta subunit interacts with rotating F0: activates and catalyzes formation of ATP
  • ATP released into matrix along with H+ that passes through channel

ADP-ATP TRANSPORTER

  • Antiporter
  • Driven by the electrical potential across membrane
  • Intermembrane space more positive than matrix
  • ATP has -4 charge while ADP has -3 charge
  • Charge difference favors movement of ATP OUT of negatively charged matrix

PHOSPHATE TRANSLOCASE

  • Symporter: pumps H+ & Pi from intermembrane space into matrix
  • Driven by pH gradient across inner membrane
  • pH greater in matrix (more basic, less H+) and lower in intermembrane space (more acidic, more H)
  • Protons & Pi move from intermembrane space into matrix
  • For every 4 H+ pumped into matrix: 3 drive ATP synthase & 1 drives Pi transport

CLINICAL CORRELATIONS

Uncouplers

  • Proteins that make inner mitochondrial membrane permeable to H+
  • Example: 2,4 dinitrophenol (DNP)

Brown adipose tissue (BAT)

  • Specialized adipose tissue that facilitates non-shivering thermogenesis
  • Contains many mitochondria & uncouplers

Leave a comment