L12 - The Electron Transport Chain

Outer membrane of mitochondria allows

small molecules and ions to pass and is freely permeable

Inner membrane of mitochondria is impermeable to

most small molecules and ions

Inner membrane space is between

inner membrane and outer membrane

Inside inner membrane is the

matrix

Inner membrane have integral membrane proteins for

ETC and transport proteins

Energy is transduced and captured through

electron transport

More negative reducing potential (greater tendency to donate electrons) drives the electron transport to

more positive reducing potential (greater tendency to accept electrons)

ΔE =

acceptor - donor

ΔG =

-nFΔE

Hydrolysis of ATP has a high negative ΔG and is ___________ than the synthesis of ATP

7x more energy

Inhibitors are used to determine sequence events of

electron transfer

NADH is reduced form of

NAD+

FADH2 is fully reduced from of

FAD

FAD and FMN accept electrons

one at a time

Heme are

iron containing porphyrin ring

Hemes are part of

cytochrome

Cytochrome is an

electron carrier and has three classes a, b, and c; Fe³⁺ or Fe²⁺ depending on whether it’s being oxidized or reduced

Ubiquinone (CoQ/Q) is a

lipid-soluble benzoquinone that has a long hydrocarbon change and freely diffuses in the inner mitochondrial membrane. Can accept one or two electrons (semiquinone).

Q is fully

oxidized

QH is

semiquinone

QH2 is fully

reduced - ubiquinol

Iron sulfur centers participates in

one electron transfer

Complex 1 (ubiquinone oxidyl reductase/NADH dehydrogenase)

• Large L shape enzyme

• Firmly embedded in the inner membrane (integral)

• Catalyzes NADH + H⁺ + Q → NAD⁺ and QH₂

• FMN accepts 2e^- from NADH + H⁺

• Pumps protons from matrix (n) to intermembrane space (p)

• Creating a proton gradient which creates potential energy

• Series of Fe-S centers accepts electrons

Complex 2

• Succinate dehydrogenase converts FAD to FADH₂ (Recall TCA)

• Not pumping protons 

• CoQ accepts electrons from complex two and is reduced to QH2

• Series of Fe-S centers accepts electrons

• FAD has less energy than NADH

Complex 3

• QH₂ oxidized

• Proton pumping

• Iron sulfur centers and cytochromes pass around electrons to cytochrome c where QH₂ → Q

• Cytochrome C is mobile and is an electron acceptor/carrier

• Cytochromes present b and c

• Cytochrome C - soluble peripheral protein of intermembrane space

Complex 4

• Cytochrome C in reduced form transfers electrons into complex four

• Large dimeric 

• 3 subunits

• Contains Heme a and Heme a₃

• Passes electrons from a series of Hemes, O2 accepts electrons, makes water

• Pumps protons

• Cyanide (CN^-) inhibits

ETC Net Equation and summary

Electrons from NADH pass Complex I to CoQ, Succinate dehydrogenase on Complex II also pass electrons to CoQ. This is all passed through Complex III, then CytC, and lastly through Complex IV, where O₂ accepts and turns into water. Complex I, III, and IV facilitate H⁺ pumping to P side.

Net eq: 2 NADH + 22H⁺_N + O₂ → 2 NAD⁺ + 20H⁺_P + 2H₂O

22H on mitochondrial (N/negative) side is either pumped to intermembrane space (P/positive) or converted to water

Inhibitors of ETC Complexes

Rotenone: Complex I

Antimycin A: Complex III

CN^- or CO: Complex IV