LECTURE 12 - REDOX REACTIONS Flashcards
where does the ETC happen?
in the cristae
what is the difference between the outer vs inner membrane of the mitochondrion?
the outer membrane is porous, molecules can easily come in from the cytosol
the inner membrane is not very porous but it has transporters
where does the CAC happen?
in the mitochondria matrix
where does the energy for proton pumping come from?
comes from electron flow, which come from NADH and FADH
how many protons are pumped by each complex?
complex 1: 4
complex 2: 0
complex 3: 4
complex 4: 2
how many protons are pumped per two electrons?
per 2 electrons you have 10 protons pumped and 1 oxygen molecules turned into water
how does oxygen get all the electrons at the end?
has the highest reduction potential
every subsequent redox center has a higher reduction potential, this keeps the electrons moving
what are the different redox centers?
iron-sulfur clusters
cytochromes or flavoproteins
what does the pumping of protons inside the intermembrane space cause?
causes a disequilibrium of protons
lots inside the membrane, positive charge, and negative charge outside
this creates an electrochemical gradient, or also a proton motive force
what is the difference between the matrix and the intermembrane space and what is that equivalent to?
the difference is 150-200mV
when you take into account the size of the mitochondria, that is equivalent to a lighting bolt
which complexes donate to CoQ?
complex I and II
what does CoQ donate to?
donates to complex III and cytochrome C
what are flavoproteins?
have a flavan mononucleotide (FMN) or dinucleotide (FAD)
can accept and then donate electrons
what powers complex V (ATP synthase)?
complex V is powered by the energy released by complexes I, II and IV
what does cytochrome C do?
shovelling protein
takes electrons from complex III and than gives them to complex IV
what is complex IV?
cytochrome oxidase
the electrons from cytochrome will go to oxygen to make water
what are the metals in the ETC?
diverse array of metals like Fe, Cu and heme
the standard reduction potentials depend on the microenvironment
what is the structure and function of complex I?
- pumps 4 net protons
- made of 44 proteins, that come from 2 different genomes
- 7 of the proteins are coded in mitochondrial DNA, which means that coordination is needed between mitochondria and nucleus to make and assemble those proteins
- complex I has a hydrophobic arm (alpha helix) in the membrane
- has a hydrophilic arm which points into the matrix
- FMN is the first redox center, then it’s iron sulfur clusters, and finally ubiquinone
what does complex II do?
does not pump protons
contributes to membrane potential by feeding electrons into the Q pool
what are pathways that reduce CoQ?
- complex I
- complex II
- multiple dehydrogenases which are also FAD bound
they impinge upon ETF (electron transferring flavoprotein)
ETF also has an FAD
passes it onto ETF-QUO
which finally donates it to CoQ
succession of redox centers on different molecules
what does complex III do?
pumps 4 net protons
receives protons from ubiquinol
what are the different forms of Q?
Q=ubiquinone
QH=semi-quinone
QH2=ubiquinol
explain the Q cycle
- QH2 comes into complex 3, 2 protons are pumped
- one electron is donated to cytochrome C, the other one goes to a Q molecule to make QH
- the cycle starts again, with another QH2, and 2 protons are pumped again
- one of the electrons from the QH2 goes to cytochrome C and the other one goes to QH, which regenerates QH2
- the cycle can start again
- total 4 electrons: 2 cytochrome C and 2 to make QH2 again
- cytochrome C will donate these electrons to complex IV
how are these complexes arranged?
arranged into one super complex called the respirasome
for the same reasons as the PDC, it is more efficient that way, if they are all close together
what is the equation for the ETC, and how much energy is released?
NADH+ (H+)+ 1/2O2 –> (NAD+)+H2O=-220kJ/mol
what are the reduction potentials of NAD+ and oxygen?
NAD=-0.32V
oxygen=+0.82V
in which reduction direction do electrons flow?
from low to high reduction potential
what is the energy from ATP hydrolysis and how does it compare to the ETC?
energy from ATP hydrolysis is 50kJ/mol
and if there are 2.5ATP/NADH that is 125kj/mol
there is more that enough harvested to make ATP
why are there so many redox reactions instead of one big one?
there are multiple redox reactions, so the energy is slowly harvested over the multiple step rather than having a big explosive step
what are the two shuttles for cytosolic NADH to the mitochondria?
G3P shuttle
malate/aspartate shuttle
how does the G3P shuttle work?
- in the cytosol, DHAP is reduced by NADH to make G3P
- G3P enters through the outer membrane, carrying the electrons from NADH
- on the inner membrane is G3P dehydrogenase, which will oxidise G3P back to DHAP
- the electrons from G3P will go onto FADH2 and then onto CoQ in complex III
- DHAP returns to the cytosol to be used in the next cycle of this reaction
how does the malate/aspartate shuttle work?
- oxaloacetate is reduced by NADH to malate
- malata enters the mitochondria
- malate is reoxidated to oxaloacetate, and NAD is reduced, which will then go to complex I
- oxaloacetate reacts with glutamate to make aspartic acid (amino group is donated)
- glutamate becomes alpha ketoglutarate
- aspartic acid and alpha ketoglutarate are co-transported out of the mitochondria into the cytosol
- by another transamination, alpha KG is made back into glutamate and aspartic acid is made into oxaloacetate
8 the cycle can start again
what are the two parts of ATP synthase?
F0 (in the membrane)
and F1 (in the matrix(
reversible enzyme
how many ATPs are made per every 360°C turn?
3 ATPs/turn
how many c subunits of F0 in mammals?
8 subunits, therefore 8 protons can come in
8 protons per 3 ATP
other organisms have a different number of subunits
explain why 2.5ATPs are made per NADH?
this is also the P/O ratio through complex 1
8 protons go through ATP synthase, which generates 3 ATP
8/3=2.7 protons/ATP
but, the Pi is co transported with another proton, which means that it is actually 3.7 protons/ATP
NADH goes through all the complexes, therefore 10 electrons are pumped through the ETC
10/3.7=2.5
that is where we get 2.5ATP/NADH
explain why 1.5ATPs are made per FADH?
this is also the P/O ratio through complex 2
8 protons go through ATP synthase, which generates 3 ATP
8/3=2.7 protons/ATP
but, the Pi is co transported with another proton, which means that it is actually 3.7 protons/ATP
FADH skips complex 1, therefore 6 electrons are pumped through the ETC
6/3.7=1.5
that is where we get 1.5ATP/FADH
