Metabolism - ETC and Oxidative Phosphorylation

Glycolysis yield:

2 ATP per glucose (1 per pyruvate)

Citric acid cycle yield:

2 ATP per glucose (1 per pyruvate)

Free energy is stored in the reduced forms of NAD+ and FAD

NADH and FADH2

How to Get the Energy?

Free energy is liberated by the oxidation of NADH and FADH2

Electrons (and hydrogen) passed to a final electron acceptor

Electron Transport Chain

Function of Electron Transport Chain

Re-oxidize NADH and FADH2 / Convert stored energy from NADH and FADH2 into a form where it can be used to synthesize ATP

Electron Transport Chain
• Byproducts:

Consumes Oxygen and Releases Water

Types of Electron Carriers: Flavoproteins
• Use as a prosthetic group either:

FAD and FMN / Transfer both electrons and protons

Types of Electron Carriers: Iron-Sulfur Proteins

Aka nonheme iron proteins / Iron-sulfur center containing iron and sulfur complexed with cysteine / The iron is the electron carrier!

Types of Electron Carriers: Cytochromes

Contain a heme prosthetic group / Iron is the electron acceptor / Do not transfer protons

Types of Electron Carriers: Copper-Containing Cytochromes (part 1)

Contain a heme prosthetic group complexed to copper 

Types of Electron Carriers: Copper-Containing Cytochromes (part 2)

Cu group holds oxygen bound until the oxygen has picked up 4 electrons and 4 protons / Then the oxygen is released as water

Types of Electron Carriers: Coenzyme Q Part 1

The only nonprotein component of the ETC / Most abundant electron carriers in the membrane

Types of Electron Carriers: Coenzyme Q Part 2

Reduced in 2 successive 1-electron (and 1-proton) steps

Sequence of Electron Transport

Dictated by reduction potential

Reduction potential:

The affinity a substance has for electrons (Measured in volts)

Positive: high affinity

Good electron acceptor

Electron carriers are organized into 4 types of respiratory complexes

Complex I, Complex II, Complex III and Complex IV

Complex I (Part 1)

Transfers electrons from NADH to Coenzyme Q and Complex I is also called NADH dehydrogenase (Complex of >40 polypeptides)

Complex I (Part 2)

Receives electrons from NADH, Transfers to FMN, Transfers to an Fe-S center and Transfers to CoQ

Complex I (Part 3)

The ETC’s purpose is to Transfer electrons and Pump protons

Complex I (Part 4) function

Transfers 2 electrons and Pumps 4 protons

Complex II (part 1)

Transfers electrons from succinate to FAD to create FADH2 (No protons are pumped!)

Complex II (part 2)

Then transfers from FADH2 to 3 Fe-S centers and Then to CoQ

Complex III (part 1)

Also called the cytochrome complex, Accepts electrons from CoQ, and Transfers to cytochrome b

Complex III (part 2)

Transfers to cytochrome b, Then to Fe-S center, Then to cytochrome c1, and Then to cytochrome c

Complex III (part 3)

Transfers 2 electrons and Pumps 4 protons!

Complex IV (part 1)

Transfers electrons from Cytochrome C to oxygen, Cyt c→Cyt a, Cyt a → Cyt a3, Fe-Cu center and Oxygen

Complex IV (part 2)

Transfers 4 electrons (Reduces oxygen to water) and Pumps 2 protons per electron pair

Summing Up the ETC (Electron Transport Chain)

Total 10 protons pumped! Eventual ATP yield: ~3 ATP per NADH and ~2 ATP per FADH2

 

How Do We Synthesize ATP? (Part 1)

Couple endergonic ATP synthesis with exergonic flow of protons and ATP synthase!

How Do We Synthesize ATP? (Part 2)

Large electrochemical gradient and Produces proton motive force

ATP Synthase Complex
• 2 Components:

Fo portion and F1 portion

ATP Synthase Complex: Fo Portion (part 1)

Embedded in the inner mitochondrial membrane / Static Component: Stalk connecting Fo and F1

ATP Synthase Complex: Fo Portion (part 2)

Mobile Component: Ring of 10 subunits / Channel through which protons move

ATP Synthase Complex: F1 Portion (part 1)

On the matrix side of the inner membrane. Static Component: Catalytic Site and Site of ATP synthesis

ATP Synthase Complex: F1 Portion (part 2)

Mobile Component: Central stalk attached to ring of Fo and Rotates inside the catalytic ring

How Does the F1 Portion Synthesize ATP? (part 1)

As the gamma subunit rotates, the beta subunit changes conformation

How Does the F1 Portion Synthesize ATP? (part 2)

Open Conformation / ADP and P bind

How Does the F1 Portion Synthesize ATP? (part 3)

Loose Conformation / ADP and P held loosely in place

How Does the F1 Portion Synthesize ATP? (part 4)

Tight Conformation / ADP and P forced together to make ATP / ATP dissociates

Putting It All Together
• Total yield from ETC to oxidative phosphorylation

10 NADH + 10 H⁺ + 2 FADH₂ + 6 O₂ + 34 ADP + 34 P_i —→ 10 NAD⁺ + 2 FAD + 12 H₂O + 34 ATP