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Biochemistry 2280A Lecture Notes - Intermembrane Space, Atp Synthase, Electrochemical Gradient

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Eric Ball

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15 – ATP synthesis
Proton gradient from electron transport chain
Electron transport chain pumps protons out of the mitochondrial matrix
Intermembrane space pH ~ 7, Matrix pH ~ 8; intermembrane more acidic
therefore more protons
Proton Motive Force
Two components:
Concentration gradient
More protons in intermembrane space, they want to diffuse to lower concentration
Electrical potential
Consequence of the fact that proteins are positive and there is no counter ion being moved across
the membrane with them; accumulates a positive charge on the intermembrane space side of the
inner mitochondrial membrane
Positives want to get into the more negative side membrane potential
Electrical potential contributes more strongly then the concentration difference.
Chemeosmotic hypothesis: protonmotive force drives the synthesis of ATP: destruction of proton gradient
inhibits ATP synthesis
F1F0 ATP synthase
A protein complex that allows protons to flow down their electrochemical gradient
The energy from this proton movement is used to make ATP; couples movement of
protons to ATP synthesis
ATP is made in the matrix
Smallest rotary motor we know
E.coli F 1F0
F0 -rotor
Transmembrane section
3 subunits: ab2c10
Proton channel
F1 - stator
membrane section
5 subunits:
α3β3γ δ ε
Makes ATP
Each c subunit binds one proton
Ring of c subunits rotates in membrane, moving protons to a channel formed
with α subunit, allowing protons to be released into matrix
γ and ε subunits (control stalk) rotate with the c subunits, and the long
curved α-helices from the γ subunit extended into the α3β3 hexamer and causing a conformational change
in the β subunits
Each β subunit has a catalyrtic site for ATP synthesis, and the conformation changes drive synthesis of ATP
from ADP and Pi
The α3β3 hexamer is prevented from rotating by a “peripheral stalk”, composed of the two b subunits and
Long slender b subunits anchored to a subunit in membrane and δ helps bind b to α3β3
Roles of each subunit
a – helps form proton channel; anchors b2 in membrane
b2 – forms a second stalk (the stator) that prevents α3β3 from rotating
c10 – helps form proton channel; rotates during proton movement
α3β3 – form active sites (one on each
β); conformational changes in α3β3
γ - forms part of central stalk; rotates
with c10 to cause conformational
changes in α3β3
δ - helps attach b2 to α3β3
ε - helps assemble complex; inhibits
ATP hydrolysis
Net reaction of ATP synthase
For each full roation of the c10 ring:
10 protons cross the membrane
3 ATP’s are made
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