Complex 1

NADH is oxidized to NAD+. comp 1 is a proton pump making active transport. energy from high energy e- is used to pump h+ from matrix to the inner membrane space against the [ ] gradient

Complex 2

FADH2 oxidized to FAD. comp 2 accepts e from fadh2 which gets oxidized back to fad. e- get transfered from fadh2 to complex2. NAD+ and FAD are free to go back to cytoplasm and matrix is collecting more e-

Complex 3

e- from comp 1 and 2 get transfered to complex 3. complex 3 is also a proton pump along with complex 1. energy from these e- used to move h+ against [ ] gradient. there's a low [ ] of h+ in matrix and high [ ] of h+ in the inner membrane space. the energy from the e- is used to pump the h+ from the matrix to the inner membrane space

complex 4

e- gets transfered from complex 3 having just enough energy to pump 1 or more h+ from the matrix into the inner membrane space. the e- are transfered to O2 the final e- acceptor in respiration

FADH2 has enough energy for 2H+ ions equivalent to 2ATP