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Chemiosmosis
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)
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
- Electrochemical energy (H+ gradient) converted to mechanical energy (rotation)
- On the matrix side, ADP & Pi bind F1 beta subunit
- ATP released into matrix along with H+ that passes through channel
- 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
- 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
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