Biology 1002B Lecture Notes - Lecture 8: Electron Acceptor, Electrochemical Gradient, Atp Synthase

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15 Feb 2016
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Lecture 8 Outcomes Integrated Metabolism I Anuj Gupta 01/30/16
change in respiration rate (oxygen consumption) in isolated mitochondria by addition of
NADH, ADP, uncoupler etc.
  At 2 minutes mitochondria is added,
at 4 minutes NADH is added, at 6 minutes ADP + Pi is added, and finally at 8
minutes an uncoupler is added.
0-2 minutes (nothing)
oNo change in slope (I.e. flat slope), because there is no mitochondria
2-4 minutes (+mitochondria)
oNo change in slope (i.e. flat slope), because there is no substrate for ETC. No
way to give electrons for the ETC. (Well no appreciable change)
4-6 minutes (+NADH)
oSlope begins to decrease as there is now substrate. Electrons provided from
NADH allow the ETC to run, and the terminal electron acceptor is oxygen which
forms H2O.
oOxidative phosphorylation can occur without oxygen. The oxidative part refers to
NADH being oxidized, not that oxygen is present.
6-8 minutes (+ADP and Pi)
oSlope begins to decrease even more. This is because it becomes easier to pump
electrons into the intermembrane space. The reason it is easier is because the H+
gradient is reduced so it is easier for H+ to be pumped into the gradient by the
electrons. And since its becomes weaker more electrons are able to easily pass
through the ETC.
The gradient becomes weaker because before there was no mechanism to
dissipate the gradient. But now is a substrate to drive ATP synthase. This
opens a new pathway for electrons to get back across.
Figure from quiz. Identical to lecture, except
everything is added 2 minutes earlier
Figure from lecture
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oRate of electron transport goes up. This is called respiratory control. The rate of
oxidation of NADH is kept in check if there is no ADP or Pi available. If there is
no substrate to available to drive proton flow through ATP synthase the rate is
kept low.
Or the rate of oxidation of FADH2 and NADH is proportional to the
abundance of ADP and Pi.
Makes sense because why would you want to oxidize these
molecules if you cannot make the molecules (ATP) that you want?
8+ minutes (+Uncoupler)
oSlope becomes steeper.
oIt now becomes super easy to pump protons across the membrane. There is
nothing stopping the rate of electron transport because there are so many holes in
the membrane that you never establish a pH gradient.
oProtons never flow back through ATP synthase because for every ATP synthase
there are a 1000 molecules of uncoupler that can be used instead to get the
protons back across. Proton pumping is now really easy.
o The rate of electron transport is as high as it could possibly be. Because even
if you have function ATP synthase with ADP and Pi around, this puts a small
check on the overall rate. There is nothing stopping the rate of electron
transport if you totally uncoupled electron transport from ATP synthesis.
oTherefore you just produce heat, pumping protons with no pH difference or
proton motive force.
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