Electron Transport Chain- Shiemke Flashcards
what is the major energy source for aerobes?
oxidation of carbohydrates and fats
what is oxidation? what happens to the energy?
transfer of high energy electrons to a compound in which electrons have a lower energy. released energy is captured and used to make ATP
what is a compounds reduction potential (E)?
tendency to gain electrons. electrons move from a reducant with a more negative E to an oxidant with a more positive E
what is special about carbohydrates and fats?
both have more negative E (fats more than carbohydrates)
what values of E and G do spontaneous reactions have?
positive E, negative G
what is the best reductant?
NAD+
what is the best oxidant?
O2
what is the equation to determine the energy available from a redox reaction?
deltaE = Eox - Ered
what is the relationship between deltaE and deltaG?
deltaG = -nFdeltE
what is the electron transport chain?
a series of reduction reactions that release energy in smaller amounts that are easier to capture than if a large amount of energy was released at once (exergonic reactions)
what do oxidized organic molecules look like?
more C-O bonds (doubles)
what do reduced organic molecules look like?
more C-H bonds
under what conditions is the electron transport chain used?
aerobic (lots of O2 to be reduced to water)
what are the reducants of the electron transport chain?
NADH and FADH2
where is the electron transport chain located?
inner mitocondrial membrane
what is the electron transport chain used for?
coupled with proton pumping to build a proton gradient across the inner mitochondrial membrane (high H in inner membrane space)
what is the proton gradient created by the electron transport chain used for?
creates a charge separation (stored energy, electrical potential) that is used to convert ADP to ATP as the protons are allowed to move down the gradient, back into the mitochondrial matrix
what is proton transfer coupled to?
ATP synthase enzyme- used to make ATP
what is terminal oxidase?
O2 is converted to water
how many complexes are in the ETC?
5
how many protons does complex I pump out?
4
how many protons does complex II pump out?
0
how many protons does complex III pump out?
2
how many protons does complex IV pump out?
4
how many protons does complex V pump out?
none, 4 protons move DOWN the concentration gradient
what is the path of electrons in the ETC?
NADH–>UQ–>cytochrome C–>O2
what enzyme is used in complex I?
NADH dehydrogenase
what happens in complex I?
cytosolic NADH donates electrons to UQ in the membrane
what is the path of reducing equivalents inside complex I/
NADH–>FMN–>Fe-S (iron sulfur cluster)–> UQ
what are the cofactors required for complex I? what are their roles?
- NAD- diffusible carrier of 2 electrons, brings electrons from cytosol
- FMN- enzyme bound carrier of 2 electrons
- Fe-S- enzyme bound carrier of 1 electron, tightly bound to NADH dehdrogenase, Fe oxidation switches between 2+ and 3+ depending on the type
- UQ- diffusible electron carrier on inner membrane
how much energy is released from complex I?
-80 kJ/mol
what enzyme is in complex II?
succinate dehydrogenase (aka succinate-CoQ reductase)
what happens in complex II?
succinate (from TCA cycle) gives electrons to UQ via a series of cofactors
what cofactors are involved? what is the order of involvement?
FAD–>Fe-S–>heme (Fe2+)
how much energy is released from complex II?
-6kJ/mol (not enough to move protons)
what is the purpose of complexes I and II?
donate reducing equivalents to the UQ pool
what are other sources of electrons that reach the electron pool?
fatty acid oxidation
the glycerol-3-phosphate shuttle- brings reducing equivalents from the cytosol (NADH from glycolysis and pyruvate dehydrogenase)
where does the NADH come from that is given to complex I? why is it different?
mitochondrial matrix
NADH cannot get into mitochondria, what is inside stays and what is outside is brought to membrane via glycerol-3-phosphate shuttle and electrons are donated to FAD which donates them to the UQ pool
what enzyme is in complex III?
cytochrome c (cytochrome bc1 complex)
what happens in complex III?
UQH2 from electron pool is oxidized to UQ and Fe3+ is oxidized to Fe2+
what is the q cycle?
redox cycle in complex III
UQH2 + 2 cyt c (Fe3+) –> UQ + 2 cyt c (Fe2+)
what is cytochrome c?
water soluble electron carrier located in complex III
what is the principle transmembrane protein in complex II?
cytochrome b- has 2 hemes bl and bh (low and high)
how many electrons do cytochromes carry?
1
how much energy is released in complex III?
-35 kJ/mol
what enzyme is used in complex IV?
cytochrome c oxidase
what is the role of cytochrome b?
move electrons between UQH2 and cytochrome c
what happens in complex IV?
electrons from cytochrome c are used to oxidize oxygen to water
what does cytochrome c use to give electrons to oxygen?
2 hemes (a and a3) and 2 Cu sites
how much energy is released by complex IV?
-100kJ/mol
where does cytochrome c bind complex IV?
intermembrane space
what are the steps involved in complex IV?
- cytochrome c binds and donates electrons to copper
- copper donates electrons to Iron
- oxygen binds on the matrix side along with 4 H ions and O2 is reduced to water
what happens if one of the complexes of the electron transport chain is inhibited?
reducing equivalents can be used at the complex after the inhibited one
fewer protons are pumped into inter membrane space
inhibition of which complex inhibits the entire electron transport chain?
complex IV
what are the two components of proton motive force?
concentration gradient and membrane potential
what are the “p” and “n” sides?
p side- inter membrane space (positive, acidic)
n side- mitochondrial matrix (negative)
how much energy is needed to move 1 H+?
20kJ
what is the reaction for complex IV?
2 Cyt c (red) + 1/2 O2–>H2O + 2 Cyt c (ox)
what is respiratory control?
electron transfer can’t occur if the H gradient is full and it would take more energy than available from the ETC to pump Hs into the inter membrane space
H gradient must be depleted via ATP synthesis for the ETC to be used
why are ETC and ATP synthesis coupled?
blocking ATP synthesis (i.e. too much ATP, not enough ADP) prevents the ETC from being used (H gradient is too large, takes too much energy to put more Hs in inner membrane space)
what is an uncoupler?
removes the respiratory control requirement
allows H ions to move back into matrix without making ATP- uses ETC and oxygen
(dissapates H gradient in mitochondria)
what are examples of electron uncouplers?
membrane weak acids- carries H ions across the membrane
ionophores- carry K ions across the membrane
how many H ions are pumped out per NADH?
10
what are the subunits of ATP Synthase?
F1- catalytic site
F0- proton channel
Describe the F1 subunit of ATPase
3 alpha and 3 beta subunits
have sites for adenine nucleotide binding (3 sites, onion each beta subunit)
describe the F0 subunit of ATPase
12 subunits that bind protons
as proton moves through, it requires a conformational change of gamma subunit, which changes the beta subunit conformation
what is the gamma subunit of ATPase?
connector between F1 and F0 subunits, rotates when protons move through F0, induces conformational change of beta subunits of F1
what are the 3 conformations of a beta subunit?
tight- ADP and P combined to make ATP
open- ATP leaves
loose- ADP and P enter
how many rotations of F0 are needed to make 1 ATP?
4 (4 protons per ATP molecule)
how many ATPs are made using a complete rotation of gamma subunit of F0 of ATPase?
3- 12 subunits/4 protons per ATP = 3 ATP
can ATPase run in reverse? why?
yes- used in bacteria when there is no O2 available
what is the P/O ratio?
how many ATP are made per electron pair
how does the P/O ratio change?
depends on where reducing equivalents enter the ETC cycle
NADH- 10/4=2.5
UQH2- 6/4 = 1.5
what is the total energy yield from complete oxidation of glucose? where do the ATPs come from?
32 ATP
4 from substrate level phosphorylation (glycolysis, TCA cycle)
28 from ETC from reducing equivalents
is oxidative phosphorylation efficient?
not really, a lot of energy is released as heat
what processes use energy from oxidative phosphorylation?
ATP translocase- moves ADP into mitochondria and ATP out
similar to net movement of 1 proton in (ADP -3 and ATP -4)
others use it too (i.e. phosphate transporter)
what are the two shuttle systems for NADH? why are they necessary?
glycerol phosphate shuttle and malate shuttle
NADH can’t get into mitohondrial matrix on its own
how does the glycerol phosphate shuttle work?
2 glycerol-3-phosphate dehydrogenases: one in cytosol, one in inner mitochondrial membrane
NADH equivalents given to alpha-glycerol phosphate, which gives them to FAD on the outer mitochondrial membrane
FADH2 gives equivalents to UQ inside membrane
not efficient
how does the malate shuttle work?
malate in cytosol is brought in with NAD to the mitochondria
reduced to NADH + Oxaloacetate
oxaloacetate is taken back to cytosol
more efficient
describe non-shivering thermogenesis?
uncoupling protein skips ATP synthesis to allow protons to enter matrix without making ATP
used to generate heat
found in brown adipose tissue (lots of mitochondria)
