Lesson 14: ETC and Oxidative Phosphorylation Flashcards
where does the source of most of the energy for ATP synthesis comes from what
the oxidation of NADH
total reduced coenxymes from glycolysis and TCA:
glycolysis: 2 ATP and 2NADH
tca (including PDC rxns_: 8 NADH and 2 FADH2
tca: 2G(A)TP
Total: 10 NADH + 4ATP + 2 FADH2
reduction of these coenzymes (along with the 3 ATP) yield an approximate energy return of
40%
- much larger energy is needed
electron transport and ATP production occurs in the mitochondria around
9-11%
ETC carries out oxidation of
NADH and FADH2
1 - electrons are passed through a series of. e- carrying molecules based on standard reduction potential
2 - electron carrying complexes are ordered in the inner membrane from low to high standard reduction potential
how are the ETC components “ordered” in the IM
from low to high standard reductio potential
standard reduction potentials of the major respiratory electron carriers:
NADH –> FMN
-69.5 kJ/mol
FMN –> CoQ –> cytb –> cyt c1 -> cyt c –> cyt a
- 36.7 kJ/mol
cyt a –> cyt a3 –> O2
-112 kJ/mol
energy is released (exergonic) as electrons move from
reduced coenzymes through the ETC to O2 in a stepwise fashion
where are we in the cell
mitochontrial matrix w/ atp synthase complexes?
- massive surface area for components of the ETC. More ATP synthase molecules = more ATP
ATP synthesis:::::
1961 : Peter Mitchel postulated the “chemiosmotic theory” - the free energy of e- transport is consevrved by pumpong H+ to the IM space. The electrochemical potential of this proton gradient is harnessed to synthesize ATP
- enzyme responsibe for ATP synthesis = ATP synthase
- IM impermeable to H+ diffusion, therefore, specific proton carrier that channels H+ down concentration gradient
F1 component of ATP Synthase
- catalytic component
- 3 alpha and 3 beta subunits (not the same as Hb), and 1 gamma
- the 3 beta subunits are responsible for ADP + Pi –> ATP (responsible for the synthesis, doing the actual chemistry)
F0 component of ATP Synthase
- embedded in the IM
- functions in H+ transport as H+ moves down the concentration gradient; rotation of C ring (rotational energy drives)
structure of the ATP Synthase is () conserved
evolutionarily
- bacterial and eukaryote yeast complex very similar
bacterial ATP synthase complex strucutre
F0 = in cell membrane
F1 = in cytoplasm
yeast ATP synthase complex structure
F0 = in inner mitochondrial membrane
F1 = mitochondirial matrix
protons move through a subunit of
F0
movement of H+ results in
rotation of C ring and gamma subunit
rotation of gamma drives
conformational changes in beta subunits F1
H+ flux translates potential energy into
rotational energy
- H+ binds to negatively charged Asp (alpha unit)
- protonated Asp 59 residues in C ring rotate
- H+ dissociates from Asp due to electrochemical gradient
How is ATP synthesized: 3 phases
- translocation of H+
- chemistry step: formation of phosphoanhydride bond
- couple H+ gradient with ATP synthesis
Binding change mechanism beta - subunit exists in 1 of 3 conformational states:
O (open) = low affinity state for substrate or product
L (loose) = ADP and P i (inorganic phosphate) binding state
T (tight) = catalytic stite ADP + Pi –> ATP
the gamma subunit rotates in a counterclockwise direction as viewed from the matrix side
- as this happenes, each beta subunit is either in the O, L, or T state and it changes each time
two famous biochemical experiments demonstrated how the rotation of the gamma induces conformational changes in the beta subunits
1
- actin filament is fluorescent –> attached this actin filament to the gamma subunit on the same side as the membrane
- as ATP hydrolyzed to ADP + Pi, gamma rotates counter clockwaise
- ATP “running in reverse” in vitro (ATP + H2O –> ADP + Pi)
- counterclockwise rotation can be observed with fluorescense microscopy, making ATP synthase run in reverse
2nd experiment for conformational changes in beta subunits
magnetic bead can be rotated by an electromagnet
- magnetic bead is on the same side as the membrane and is attached to the streptavidin linker, attached to the gamma subunit
- gamma rotates clockwise thanks to the electromagnet (could control rotation)
- ATP synthesized in vitro (ADP + Oi –> ATP)
