4A: The Citric Acid Cycle / 4B: Electron Transport and Oxidative Phosphorlyation

what is the purpose of the pyruvate dehydrogenase complex?

it includes 3 types of enzymes that collectively remove a carboxylate group from pyruvate and produce acetyl-CoA and NADH for the CAC

how is the pyruvate dehydrogenase complex regulated?

inhibited by NADH, ATP, and Acetyl-CoA and stimulated by NAD+, AMP, and CoA

where does the citric acid cycle (CAC) occur?

in the mitochondrial matrix

where does the pyruvate dehydrogenase reaction (PDR) occur?

in the mitochondrial matrix

what are anaplerotic reactions?

they replenish citric acid cycle intermediates - occurs during the unfed state, takes it’s intermediates for itself

what is the role of the citric acid cycle?

it is a source of precursors for biosynthesis, intermediates are recycled

what are the net products of the CAC?

3 NADH, 1 FADH2, 2 CO2, 1 GTP

what is the regulation for the first irreversible step of CAC?

oxaloacetate → citrate : citrate can inhibit citrate synthase (and NADH)

what is the regulation step for the second irreversible reaction of CAC?

isocitrate → alpha-ketoglutarate : alpha-ketoglutarate can inhibit it’s own and citrate synthase (and NADH)

what is the regulation at the third irreversible step of CAC?

alpha-ketoglutarate → succinyl-CoA : alpha-ketoglutarate can inhibit it (and NADH)

where in the cell does the electron transport chain (ETC) occur?

the mitochondria - protons are pumped from the matrix to the intermembrane space

what does complex 1 do with ubiquinone (Q)?

it binds and transfers 4 protons from the matrix to the IMS

what does complex 2 do?

it transfers electrons but does NOT pump protons - electrons are carried by FADH2 to Q

what does complex 3 do?

it transfers electrons from ubiquinol to cytochrome c - 4 protons are pumped into the IMS

what does complex 4 do?

oxidizes cytochrome c and reduces O2 - for every 2 electrons donated by cytochrome c, 2 protons are pumped into the IMS and reduces O2 to H2O

what is the path of NADH in the ETC?

complex 1 → Q → complex 3 → cyt c → complex 4 → O2

how does the proton motive force drive ATP synthesis?

from the chemiosmotic theory - the build up of protons creates an imbalance and represents a source of free energy

what is the chemiosmotic theory?

the proton translocating activity of the ETC in the inner mitochondrial membrane generates a proton gradient across the membrane - the imbalance of protons represents a source of free energy (potential energy)

how does the proton gradient produce ATP via ATP synthase?

both the proton concentration and charge contribute to the free energy of the proton gradient - it binds ADP and Pi to phosphorylate ADP, and release ATP

what is the structure of ATP synthase?

F1 - 3 active sites, alpha beta subunits

F0 - c ring that rotates, causing the gamma shaft to rotate

what is the path of succinate/FADH2 in the ETC?

complex 2 → Q → complex 3 → cyt c → complex 4 → O2

F1 of ATP synthase

alpha-beta hexamer - does not rotate because it is held in place by a peripheral arm anchored to the alpha subunit - has loose, tight, and open active sites

loose active site

bind to ADP + Pi, directly to the right of the open site

tight active site

ATP synthesized, to the right of the loose site

open active site

low affinity for substrate and product, lets go of ATP

oxidative phosphorylation

H+ gradient drives ATP synthesis - rate depends on the rate of fuel catabolism, regulated by the availability of reduced electron carriers

what are uncouplers?

reduce/prevent ATP synthesis, but do not reduce/prevent the electron transport (they speed it up) - protons leak back into the matrix and e- transport continues without any ATP being made, they are “uncoupled”

what is the reactive oxygen species (ROS)?

O2 is the final e- acceptor - can form when a free radical (atom/molecule with a single unpaired e-) seeks for another single e- and can cause damage to DNA (involved in aging) but can serve as important signals to cells

how is glutathione reductase and peroxidase work together to deal with ROS?