Electron Transport Chain + Oxidative Phosphorylation

24

how many electrons oxidized through the oxidation of glucose to CO₂?

cristae

ETC doesn’t happen in every region of inner mitochondrial membrane, only in the _____

mitochondria inner membrane

what membrane in the cell has the most proteins?

mitochondria inner membrane

only permeable to H2O, CO2, O2

mitochondria outer membrane

contains porins and is freely permeable to molecules up to 10 kDa

malate/aspartate shuttle

• completely reversible

• cytoplasmic NADH produces 3 ATP

glycerol phosphate shuttle

• irreversible

• cytoplasmic NADH produces 2 ATP

malate/aspartate shuttle

• move malate + 2 electrons (NADH) into mitochondria for ETC

• oxaloacetate in cytoplasm converted to malate

• malate carries electrons from NADH across the membrane then gives the electrons to NAD+ → NADH

malate/aspartate shuttle

• oxaloacetate formed in mitochondria during TCA needs to be transported to cytoplasm for gluconeogenesis

• converted to aspartate which crosses inner membrane then converts back to oxaloacetate

glycerol phosphate shuttle

• feeds electrons from cytoplasmic NADH directly into ETC without transporting it into mitochondria first

• used in human brain and flight muscles in insects

glycerol phosphate shuttle

electrons transferred from NADH → DHAP (forms phosphoglycerol) → FADH₂ → ETC complex II

redox reaction energy

• change in standard Gibbs = -n*F* standard reduction potential

• n = number of electrons transferred

• F = Faraday’s constant (96.5 kJ/volt)

• std. reduction potential of acceptor - donor

spontaneous

reduction reactions with a high reduction potential give off large amounts of energy because they are more ___

ETC reaction

• NADH + H⁺ + ½ O₂ → NAD⁺ + H₂O

• 2 electrons transferred

-218 kJ/mol

standard free energy change of ETC reaction

complex I inhibitors

rotenone and amytal (fish poison)

complex III inhibitor

antimycin

complex IV inhibitor

cyanide

NADH-UQ reductase (NADH dehydrogenase)

• complex I

• oxidizes NADH (takes e- from NADH)

• reduces coenzyme Q (gives e- to Q)

complex I (NADH-UQ reductase or NADH dehydrogenase)

electrons flow from NADH → FMN → Fe-S → CoQ

complex I (NADH-UQ reductase or NADH dehydrogenase)

has at least 45 protein subunits in humans

4

how many protons pumped out per NADH in complex I (NADH-UQ reductase or NADH dehydrogenase)?

ubiquinone (Q)

most oxidized form of coenzyme Q with two ketone groups

semiquinone (QH radical)

reduce ubiquinone with 1 electron and 1 proton

ubiquinol (QH₂)

• reduce semiquinone (QH radical) with another electron and proton

• most reduced form with two alcohol groups

succinate-UQ reductase (succinate dehydrogenase)

• complex II

• oxidizes succinate → fumarate (takes e- from succinate)

• reduces Q (gives e- to Q)

complex II (succinate UQ-reductase or succinate dehydrogenase)

electrons flow succinate → FAD → Fe-S → UQ

0

how many protons are pumped out of complex II (succinate UQ-reductase or succinate dehydrogenase)?

4Fe-4S, 3Fe-4S, 2Fe-2S

three types of Fe-S clusters in complex II (succinate UQ-reductase or succinate dehydrogenase)

4

how many subunits including 2 Fe-S proteins are there in complex II (succinate UQ-reductase or succinate dehydrogenase)?

not enough energy

why does complex II (succinate UQ-reductase or succinate dehydrogenase) not pump any protons?

CoQ-CytC oxidoreductase

• complex III

• oxidizes QH₂ (takes e- from QH₂)

• reduces Cytochrome C (gives e- to Cyt C)

complex III (CoQ-Cyt C reductase)

electron flows from UQH₂ → cyt c

4

how many protons pumped out through complex III (CoQ-Cyt C reductase)?

Q cycle

• redox cycle where electrons are passed from UQ to cyt c and pumps H+ out

• needed because UQH₂ has 2 electrons to give but cyt c can only carry 1 electron

b cytochrome (hemes b_L and b_H)

principal transmembrane protein in complex III (CoQ-Cyt C reductase)

UQH₂

lipid soluble electron carrier

cytochrome c

• water soluble electron carrier

• loosely associated with inner mitochondrial membrane when shuttling electrons between complexes

cytochromes

heme-containing electron transport proteins

1

how many electrons can cytochrome c carry?

semiquinone (UQ- radical)

• in the Q_p site, the first UQH₂ gives 1 electron to cyt c and 1 electron to UQ (from membrane) in the Q_n site forming ___

• pumps out 2 H+

ubiquinol (UQH₂)

• in the Q_p site, the second UQH₂ gives 1 electron to cyt c and 1 electron to UQ- radical (semiquinone) in the Q_n site forming ____

• pumps out 2 H+

cytochrome c oxidase

• complex IV

• oxidizes cyt c (takes e- from cyt c)

• reduces O₂ (gives e- to O₂)

2 H+ (but always works in batches of 4 e-)

how many protons are pumped out of complex IV (cytochrome c oxidase) per 2 e-?

forms reactive radicals (O₂ + 4 e^- → H₂O)

why does complex IV (cytochrome c oxidase) work in batches of 4 e-?

I-III-IV

which ETC complexes form a supercomplex?

ATP synthesis (oxidative phosphorylation)

coupled to electron transport chain

alkaline, negative

• because of ETC, the pH inside the mitochondria is ___ and the electric potential inside is ____

• H⁺ were pumped out

21 kJ/mol

• change in Gibbs for ETC and making ATP

• dG = 2.3*R*T*d(pH) -n*F*dE

2.5

how many ATP made per 2e- (NADH)

F₀

part of ATPase that is embedded in inner mitochondrial membrane

F₁

part of ATPase that sticks into mitochondrial matrix

F₁

contains alpha-beta subunit and gamma subunit (of ATPase)

alpha-beta subunit (of F₁ part of ATPase)

• has 3 different conformations with O (nonbinding), L (loose binding), and T (tight binding) sites

• substrates don’t move between sites, the sites change conformation

L site (loose binding)

ADP is phosphorylated → ATP in the ____ of alpha-beta subunit in F₁ of ATPase

T site (tight binding)

once ADP is phosphorylated to ATP, it is in the ____ of alpha-beta subunit in F₁ of ATPase

O site (nonbinding)

once a new ATP is formed, the previous ATP that was the T site is now the ____ in alpha-beta subunit of F₁ of ATPase and is EJECTED

gamma subunit

the movement of 3 H+ rotates the _____ 120 degrees and changes the binding site conformations in alpha-beta subunit of F₁ ATPase

3

9 H+ pumped = three 120 degree rotations = 1 full revolution of alpha-beta subunit = ___ ATP produced

H+ gradient

ATPase requires ____ to work

uncouplers

stop ATP production by inducing H+ leak into mitochondrial matrix (disrupts gradient)

2,4-dinitrophenol (DNP)

insecticide known to uncouple mitochondrial oxidative phosphorylation

uncoupling proteins (UCP)

• naturally occurring proteins that induce proton leak into mitochondrial matrix

• drains proton gradient without making ATP

• produces ALOT of heat

heat

all ETC reactions are exothermic, so without ATP production there is a lot of ____

brown fat

tissue that has uncoupling proteins (UCP) that drain proton gradient to produce more heat

UCP1

• uncoupling protein in humans for brown fat to keep warm

• knock mice don’t have this gene so they are more sensitive to cold

UCP2

uncoupling protein broadly expressed (including brain) to protect neurons against free-radical induced death

UCP3

• uncoupling protein expressed in muscle

• overexpression → lean mice

superoxide dismutase

converts superoxide (O₂^- radical) to hydrogen peroxide (H₂O₂)

catalase

converts hydrogen peroxide to water and oxygen

glutathione peroxide

converts any peroxide (R-OOH) to an alcohol (ROH)

superoxides

Se, Vit E, Vit C, uric acid pick up electrons from ____ to detoxify