Electron transport chain (lec 18)

Recap of oxidative metabolism

• Glycolysis + PDH

  • Step 1: make pyruvate (3C)

  • Step 2: make acetyl-CoA (2C)

• TCA

  • add 2C from acetyl-CoA to OAA to make citrate

  • burn 2C from citrate to regenerate OAA

• Oxidative phosphorylation (OX-PHOS)

  • uses all the e- generated in this process to make a bunch of ATP

can NADH cross the mitochondrial membrane?

no it can’t

what is electron shuttle mechanism I

Glycerol phosphate shuttle

what does glycerol phosphate shuttle do

1. DHAP is reduced by NADH (cytoplasmic) to glycerol-3-phosphate in the mitochondrial membrane

2. FAD (mito) is reduced to FADH2 by glycerol-3-phosphate which is oxidized back to DHAP

what is 2nd electron shuttle mechanism

Malate-aspartate shuttle (MAS)

what goes on in malate-aspartate shuttle (MAS)

key idea: makes sure elections from reduced NADH gets across

• malate and aspartate are transported by exchange proteins in 1:1 ratio

  • every malate into mitochondria = 1 ⍺KG into cytosol

  • every aspartate into cytosol = 1 glutamate into mitochondria

• ⍺KG and glutamate are used to regenerate OAA and aspartate

what are the new cofactors in the ETC

• inorganic FeS centers

• cytochromes

• ubiquinone (coenzyme Q)

which of the two enzymes transfers electrons

1. cytochromes

2. ubiquinone (coenzyme Q)

which complexes produce a proton gradient, H+

complexes: I, III, IV

what does complex V do

it converts the proton gradient into ATP

how many protons does NADH pump

10H+

how many protons does FADH2 pump

6H+

Complex 1: NAD dehydrogenase

• produces 4 protons

• NADH → NAD+

• uses NADH electrons to pump protons into the intermembrane space, against the gradient—cost energy

• electrons are transferred to membrane bound ubiquinone (UQ)

Complex II: Succinate Dehyrdogenase

• is an enzyme in the TCA cycle, SDH

• FADH2 generated never leaves the enzyme

• electrons are instead transferred to ubiquinone

• no protons pumped

Complex III: Ubiquinone: Cytochrome c - oxidoreductase

• produces 4 protons

• harvest the electrons from ubiquinone made in complexes I and II

• electrons are transferred to a molecule called cytochrome c

• energy generated in this reaction pumps more protons across gradient

Complex IV: cytochrome oxidase

• produces 2 protons

• harvests the electrons from cytochrome c made in complex III

• electrons are transferred to molecular oxygen, making water

• energy generated in this reaction pumps more protons across the gradient

why is oxygen needed in ETC

cytochrome c electrons are transferred to oxygen, the final electron sink in the process

Complex V: ATP synthase

• produces 0 protons

• 4 protons per 1 ATP

• 〜3-4 ATP per turn of the synthetase

• 120º rotation per ATP cycle intermediate

• 230 rotations per second

• 20,000 rpm

How many subunits are there in F1 of ATP synthase?

5

• alpha and beta from the mushroom, the stem of gama, delta and epsilon

how many protons are pumped out per NADH

10 protons