ETC Flashcards
What do reducing equivalents do for ETC?
-add e- to ETC but not to build molecules = for energy
-pass through oxidation and reduction reactions to get energy
Where does the ETC occur?
-occurs in matrix and inner mito membrane
List examples of electron carriers
-NAD and FAD: organic carries
-Quinones: lipid carriers
-Hemes and iron-sulfur clusters: biometallic carriers
What are mitochondrial shuttles?
-transport systems used to help compounds cross the mitochondrial inner membrane
-move NADH equivalents across membrane to get e- to ETC
Name two of the mitochondrial shuttles used in ETC?
-glycerophosphate shuttle
-aspartate-malate shuttle
In terms of permeability, how are the outer and inner mitochondrial membranes different?
-outer mem is leaky
-inner mem is impermeable
What are the steps to the dehydrogenase mito shuttle?
NADH (from glycolysis) becomes NAD+ -> DHAP via GAP dehydrogenase becomes GAP -> GAP goes back to DHAP when they transfer e- to FAD on the other side of the membrane -> FAD becomes FADH2 via dehydrogenase
What are the steps for the malate/aspartate shuttle?
NADH becomes NAD+ via malate dehydrogenase -> malate enters matrix and exchanges with a-ketoglutarate (antiporter) -> malate becomes oxaloacetate in TCA via NAD+ and malate dehydrogenase -> oxaloacetate becomes aspartate and glutamate becomes a-ketoglutarate via transamination -> aspartate leaves matrix exchanges with glutamate (antiporter) -> aspartate and ketoglutarate do transamination to glutamate and oxaloacetate
Does the a-ketoglutarate and glutamate circuit in the malate/aspartate shuttle require an enzyme?
-no, just a transamination reaction
What occurs in Complex 1?
-NADH dehydrogenase
-site of NADH oxidation
-pumps 4H+ out of matrix
-e- are transferred to Q
-Q -> QH2
What are quinones?
a ring structure (the quinone) and a hydrophobic tail
What are some different forms of quinone?
quinone + 1e- + 1H = semiquinone
semiquinone +1e- +1H = hydroquinone
What occurs in Complex 2?
-succinate dehydrogenase
-generates a reduced ubiquinone (QH2)
-no protons pumped out
What occurs in Complex 3?
-cytochrome c reductase
-e- transferred to cytochrome c
-1e- at a time
-4H+ pumped out per 1 QH2
What is a Q pool?
-combination of oxidized and reduced forms of ubiquinone found in mito membrane
characteristics cytochrome c
-soluble e- carrier
-receives e- from complex 3
-has heme to carry 1e-
what is inside a cytochrome protein?
a heme
What is the issue with electron transport?
-ETC is leaky
-QH2 is 2e- carrier
-cyt c is a 1e- carrier
-radicals are bad
What is the Q cycle?
-the sequence of transferring e- from QH2 to cyt c without release radicals to the rest of the cell
What is the reaction equation for Q cycle step 1?
QH2 + Q + cyt c (oxidized) -> Q + Q.- + 2Hp+ + cyt c (reduced)
What is the reaction equation for Q cycle step 2?
QH2 + Q.- + 2Hn+ + cyt c (oxidized) -> Q + 2Hp+ + QH2 + cyt c (reduced)
What is the net equation for the Q cycle?
QH2 + Q + 2 cyt c (oxidized) + 2Hn+ -> Q + 2 cyt c (reduced) + 4Hp+
What are the steps for Q cycle part 1?
QH2 enters cytochrome b -> 2H+ leave -> 1 e- attaches to 2Fe-2S -> 1e- gets passed to heme in cyt 1 -> cyt c leaves -> the Q leaves the cytochrome but stays in the lipid mem -> the other 1e- stays with the Q as a radical inside cyt b
What are the steps for Q cycle part 2?
similar as part 1
QH2 enters cyt b -> 2H+ leave -> 1e- leaves Q to 2Fe-2S and then heme and then cyt c leaves -> 1 q leaves cyt b ->the other 1e- with the Q attaches to the initial Q radical and bring in 2H+ to bind and create QH2
What occurs in complex 4?
-cytochrome c oxidase
-takes 4e- from cyt c
-pumps 2H+ out of mito matrix
-reduces O2 and H2O
-uses other e- carriers
-O2 is terminal electron acceptor
What is a respirasome?
-aggregated supercomplex with complex 1, 3 and 4
-assists with substrate channeling
What is ATP synthase?
-aka F0/F1 ATPase
-multisubunit
-responsible for ATP production
-use electrochemical energy and chemical gradient for: ADP+Pi->ATP
What are uncouplers?
-they interfere with electron transport
-generate heat instead of ATP
What is the mechanism of ATP synthase?
-protons move between a and subunits of F0 complex
-powered by PMF
-subunit c rotates
-gamma and epsilon subunits also move through hexamer of a and b subunits
-conformation change
-binds ADP with Pi
How does ATP Synthase rotate?
-three subunits
-each have three states: open, loose binding, tight binding
-open: empty
-loose: ADP+Pi enter
-tight: ATP created
-open: ATP kicked out
What is the point of the rotation of ATP Synthase?
-the product and enzyme form is very stable and favourable = ATP wants to stay in the enzyme
-by twisting to open position, ATP is forced out
-aka rotational catalysis
How was the rotation of ATP Synthase proved?
-they tagged the rotating part with a fluorescent actin filament and watched it move
What is the proton motive force?
-electrochem potential from uneven distribution of e- across mito matrix
-involves chemical and electrical potential
What is chemical potential?
-the high concentration of protons on outside of mem compared to the inside
-expressed as ΔpH
What is electrical potential?
-added positive charge that accumulates outside the mem
-measured V or mV
-voltage drop across mem
What is the equation for Gibbs Free Energy in correlation to membrane potential?
ΔG = nℱΔΨm
-F = Faraday’s constant
What are the 5 types of ATPases?
-F
-A
-V
-E
-P
How do ATPases perform their function in reverse?
use ATAP hydrolysis
What is an ATP:ADP Translocase?
-enzyme; antiporter
-transports ATP from mito
-in exchange for ADP
-transmem integral protein with 6 a helices
-conformational change
-driven by [ ] difference between ATP and ADP
What is phosphate translocase?
-enzyme; symporter
-replaces PO4- lost as ATP
-driven by PMF
