Oxidative phosphorylation Flashcards
Describe the four complexes
Complex 1 (*aka NADH dehydrogenase): FMN (comes from riboflavin) Fe-S
Complex2 (*aka succinate dehydrogenase) yes this is the same enzyme in TCA but counts as part of both because it is embedded in membrane: FADH2 is electron donor
Fe-S
-there is no transfer of protons
Complex3: Cyt-b
Cyt-c1
Fe-S
Complex4: Copper, Iron
Cyt-a
Cyta3
How do you calculate energy change in a redox reaction?
G = -nF(deltaE)
n is the number of electrons being transferred
F = faraday constant, 23 kcal/Volt
delta E: the total of reduction potentials
a smaller E potential means poor electron acceptor, a larger E potential means good electron acceptor, high affinity.
NADH + 1/2O2 + H+ > NAD+ H2O
Half reactions of interest:
NADH + H+ > NAD+ + 2H+ +2e- = +.32
1/2O2 +2H+ + 2e- > H2O = +.82
total = 1.14
-2(23)(1.14)= -53 kcal/mol
53 kcal is released when NADH reduces O2.
However 40% of energy is used to make ATP, 60% escapes as heat
1NADH > 3 ATP, each ATP is 7.3. 3 ATP > 22 kcal.
What are the two bypass reactions?
Electrons are donated by FADH2 to coenzymeQ from G3P dehydrogenase and Fatty Acyl CoA dehydrogenase.
Note: complex two is on the matrix side of the inner membrane.
G3P-dehydrogenase is on the intermembrane space side
Fatty acyl coA DH is also on the matrix side of inner membrane.
G3P is glycolysis which is in the cytoplasm
Acetyl coA is in matrix of mitochodria (krebs)
What does Atractyloside do?
So ADP isn’t found in the matrix, it relies on an antiport ADP/ATP to get it into the matrix so that F1 can convert it to ATP.
Atractyloside prevents this exchange. THis will stop the ETC and proton gradient will build up.
What do Amytal and Rotenone do?
They inhibit complex 1.
Amytal is the truth serum, a barbiturate, used to treat anxiety, insomnia, and epilepsy, may protect cardiac muscle from ROS since ETC is a significant source of ROS.
Rotenone is a naturally occuring pesticide. It is the fish poison. no NADH can be oxidized but succinate can still enter via complex 2.
What does Antimycin do?
It is an inhibitor of complex III. It binds tightly to cytB when it is reduced.
Prevents the transport of electron to Cytc and complex 3 is left still oxidized.
Usually all four are pretty much oxidized.
Now with a block at cytb and a build up of electrons, complexes 1,2 and cytb are completely reduced while complex 3, 4 and cytc are completely oxidized.
What do cyanide, carbon monoxide do to the ETC
How does cyanide poisoning get treated?
They inhibit complex 4, the one responsible of reducing O2 to water.
Cyanide binds tightly to the oxidized iron of the heme molecule in cytochrome oxidase a3. (3+). It prevents the conversion back to 2+ so that Complex 4 can never be reduced by cyt C and all ETC stops.
The treatment is to quickly convert 20-25% of a patients hemoglobin to MetHb which is also Fe3+ to soak up any free CN in blood. This is done by sodium nitrate.
CNMetHb can then be converted to thiocyanate after the adminstering of Na-thiosulfate which is easily excreted by kidneys.
Complexes 1,2,3, cyta cyta3 are all fully reduced
complex 4 and cytochrome oxidase are fully oxidized.
What does oligomycin do?
Oligomycin binds to the Fo portion of ATP synthase. It blockss the proton pore and prevents reentry of protons into the matrix. No ATP can be made and the proton gradient builds up.
Can no longer pump protons against increasing gradent so redox reactions stop
Similar to high ATP/ADP ratio which inhibits ATP synthase.
What is 2,4 dinitrophenol (DNP)
It is an uncoupler. It will move protons from the intermembrane space into the matrix. Like all other uncouplers, the rate of respiration results in no ATP made, and rate is no longer dictated by ADP/ATP.
BMR goes really fast, all energy from the redox reactions goes to making heat, you can die from hyperthermia.
What are AraC and AZT
cytosine arabinoside) and (azidothymidine
These damage the membrane, so protons freely flow through the porous inner membrane.
How does proton channels (uncoupling proteins) affect proton gradient
Unlike the dangerous chemicals, these are naturally occuring uncoupler.
The main one is Thermogenin (UCP-1) which is found in brown adipose tissue. It transports protons in a controlled manner, no ATP is made, it is all used to generate heat.
Babies depend on Brown adipose because they don’t have the shivering ability of adults.
How is thermogenin activated?
When the brain senses cold, SNS nerves release norepi which actiavtes a lipase in brown adipose tissue which release fatty acids from TAGS. Fatty acids serve as fuel in tissue. and ACTIVATE UCP1. It transports protons from the cytosolic side of inner mitochondrial membrane back to matrix.
What is MELAS?
Complexes 1 and 4 are affected. Leading to mitochondrial encephalopathy (functioning of brain is effected, not enough energy)
lactic acidosis (no oxphos)
and stroke
Well NADH is produced in glycolysis, how does that get into the matrix for use in ETC?
There are two shuttles, malate-aspartate and glycerol phosphate.
Malate-aspartate: NADH is used to make malate, malate is exchanged with alpha-ketoglutarate. Malate is then used to make NADH and oxaloacetate. No ATP is used.
is reversible
Glycerol-phosphate shuttle: is irreversible
- essentially an NADH is used to make FADH2 with glycerol3phophate is the carrier of the electrons.
- 1 ATP net loss.
What are the effects of CN on ATP, TCA, oxphos
It decreases ATP, oxphos and TCA activity. Without NADH getting reduced, you cannot regenerate NAD+.
