TC and Chemiosmosis Demo

What are the two aspects that make of these processes together

(1) creation of proton imbalance in the mitochondrion

(2) using that imbalance/gradient to move create ATP —> oxidative phosphorylation

Oxidative phosphorylation

• Requires taxis

• ATP formed indirectly

• involves series of redox reactions where oxygen is final electron acceptor

• using the proton imbalance to create ATP

ETC overview

• A series of protein (except for Q) complexes embedded in the inner membrane of the mitochondrion (some transmembrane, some peripheral)

• Each complex is more electronegative than the one before so electrons are pulled downhill towards oxygen

  • oxygen is the final electron receptor - highly EN, only thing that will safely take the electron at the end

  • Electrons get held tighter and tighter as goes downhill so it loses potential energy

Pathway of electron pairs from NADH that are passed through ETC

1. Complex I —> NADH dehydrogenase

   • NADH drops off 2 e- and its protons left in the matrix

     • goes to pick up more electrons (not from glycolysis bc in the mitochondria)

   • Complex I goes through the membrane (so can move protons from matrix to I-M space)

2. ubiquinone (Q)

   • lipid soluble so can move freely in the membrane

3. Complex III (cytochrome b-C1 complex)

   • goes through the membrane

4. Cytochrome C (cyt C)

   • Water soluble —> moves along the outside of the membrane

5. Complex IV (cytochrome c oxidase complex)

   • most EN, e- are very stable and held tighter

   • cyanide inhibits permanently and would stop all production

Details abt the complexes

• Q is a type of lipid called quinone

• All of the other complexes are proteins that are bound to cofactors called prosthetic groups

  • the prostetic groups are what accept and donate electrons, constantly being reduced and oxidized

How does the pathway change with FADH2

• FADH2 gives its two electrons to the chain as well

• But, bc it is more EN than NADH dehydrogenase, it drops electrons at complex II —> they then get passed to Q and then cont to rest of pathway

• only 2 proton pumps activated instead of 3

Proton pumps

• As the electrons move from complex to complex, they occupy more and more stale position (bc each more EN than last) —> this releases free energy

• the free energy is used to move protons through the 3 proton pumps (complexes I, III, IV) from the matrix into the intermembrane space

Final electron receptor

• electrons bound to complex IV (cytochrome c oxidase) are very stable

• Need a highly eletronegtive substance to oxidize last complex

• oxygen stips the electrons from cyochrom c oxidase complex and adds them to two protons from the matrix

• (complex IV can only hold two electrons so oxygen needs to take them away or else process will stop)

• makes water:

2e- + 2 p+ + 1/2O2 —> H20

(2e- + 2p+ is 2H+)

Movement of cytoplasm NADHs

• 2 NADHs made in glycolysis also need to get their electrons to the matrix to get to the ETC but they are in the cytoplasm

• NADH is too large to cross —> electrons (+ proton) are dropped off outside and picked up by another taxi on inside

• 2 methods depending on type of cell —> both electron shuttles:

(1) Malate-aspartate shuttle

• found in liver, kidney, heart cells

• electrons are picked up by another NAD+ inside matrix to form NADH

• very little energy lost in the transfer

(2) glycerol-phosphate shuttle

• found in skeletal muscles, brain cells

• electrons picked up by FAD inside the matrix to form FADH2

• some energy lost as e- move across membranes

• creates an energy output diff of 2 ATP at the electron transport chain

Proton gradient

• each NADH results in the pumping (requires energy) of 3 protons into the intermembrane space

• each FADH2 results in the pumping of 2 protons into the I-M space

• formation of H2O at the end removed protons from the matrix

• converts the chemical potential energy held by the electrons from glucose into electrochemical potential energy (proton gradient)

• this electrochemical gradient is used in chemiosmosis

  • electrical component: higher + charge in the IM space

  • chemical component: higher [H+[ in the I-M space, several pH units difference

Chemiosmosis

• Uses the electrochemical gradient creates by the ETC

• this creates a potential difference (voltage) across the inner membrane

• protons diffuse through proton channels associated with an enzyme called ATP synthase

  • (***the protons diffuse through, are not pumped

  • pumping requires energ but this is passive transport

  • the protons could go straigth through the membrane bc itsn ot solid but this is less controlled, cant harness the free energy change and would be released as heat)

  • ATP synthase allows us to harness the difference in free energy

• as protons move through ATP synthase, free energy of the electrons decreases and difference is relases

• released energy drives the synthisis of ATP from ADP + Pi

• ATP molecules are then transportde into the cytoplasm and used to drive endergonic processes

ATP totals

• NADH drops electrons at the front of the ETC, 3 protons pumped

• thus 3 ATP are created for each NADH that arrives at ETC

• FADH2 drops electrons at Q —> 2 protons pumped as result

• thus 2 ATP creates for each FADH2 that arrives at ETC