Electron transport chain

Complex 1

• 2 electrons will be accepted from NADH

• Transfers them to Coenzyme Q

• Pumps 4 H⁺ into the inter membrane 

• NADH turns into NAD+

Complex 2/ Succinate Dehydrogenase

• Accepts electrons from FADH₂ 

• Transfer them to Coenzyme Q 

• Does not pump protons 

• FADH₂ turned FAD

Coenzyme Q/Ubiquinone

• carriers electrons from Complex 1 & 2 into complex 3

Complex 3/Cytochrome Bc complex

• Transfer electrons from Coenzyme Q to cytochrome C

• Pumps 4 H⁺

Cytochrome C

• Carriers electron one at a time from complex 3 & 4

Complex 4/Cytochrome C oxidase

• Transfer electrons to molecular oxygen(final electron acceptor

• Reduces o₂ to h₂ O 

• pumps 2 H⁺ per pair of electrons 

Structure of ATP Synthase( F 0 and F1)

• F₀ (membrane-embedded motor)

  • Forms a proton channel that allows H⁺ ions to flow down their electrochemical gradient.

  • Contains a c-ring of subunits that rotates when protons pass through.

  • Acts like an electric motor, converting proton motive force into mechanical rotation.

• F₁ (catalytic headpiece)

  • Located on the matrix side (mitochondria) or stroma side (chloroplasts).

  • Composed of α₃β₃ hexamer (three α and three β subunits arranged alternately).

  • The β subunits contain the catalytic sites for ATP synthesis.

  • Connected to F₀ by a central stalk (γ and ε subunits) and a stator (b subunits) that hold the α₃β₃ hexamer stationary

Structure of ATP Synthase(Rotary)

• Proton flow through F₀ drives rotation of the c-ring and central stalk (γ subunit).

• This rotation induces conformational changes in the β subunits of F₁:

  • One β subunit binds ADP + Pi.

  • Another β subunit synthesizes ATP.

  • The third β subunit releases ATP.

Structure of ATP Synthase(key structure)

• Stator arm: Prevents the α₃β₃ hexamer from rotating with the stalk.

• Rotor (c-ring + γ subunit): Rotates with proton flow.

• Catalytic sites: Located in the β subunits of F₁.

• Coupling: Mechanical rotation → chemical synthesis.

net inputs

NADH, FADH₂, O₂, ADP + Pi

Net outputs

ATP, H₂O, NAD, FAD

Location of ATP Synthase

inner mitochondrial membrane