Block 4 Nelson Questions Flashcards
How many protein coding genes in mitochondria?
13
How many proteins in mitochondria?
About 683
Permeability of Outer Mitochondrial Membrane
Porous to molecules smaller than 5 kDa
Permeability of Inner Mitochondrial Membrane
Impermeable to ions, including protons
Location of Cytochrome C
Intermembrane space
State 3 Respiration
Active state when ADP added; Significant oxygen consumption
State 4 Respiration
Resting State when ADP runs out; Low rate of oxygen consumption
Mitochondrial morphology during resting state
Matrix space large; Intermembrane space small
Mitochondrial morphology during active respiration state
Matrix space small; Intermembrane space large (pumped full of protons, water follows)
Purpose of condensed cristae during Active (State 3) Respiration
Fusion may mediate rapid exchange of metabolites with cytosol
Protein linked to Cristae morphology
Mitofilin (MINOS complex)
Mitofilin
Linked to cristae morphology; Tubular junctions eliminated in knockdown, can’t export anything to cytosol
What releases Cytochrome C
Signal from Bid, Bad, and/or Bax opens pores in outer membrane, releasing cytochrome C
Action of Cytochrome C once released
Cytochrome C and Apaf1 recruit Caspase 9, forming Apoptosome
Effect of apoptotic signal on morphology
Extensive fusion of cristae preceding Cytochrome C release
Porin protein
Beta barrel protein that forms trimers in outer membrane of mito; allows small molecules (not proteins) to pass freely
Protein:Lipid Ratio in Inner vs Outer Mitochondrial Membrane
3:1 inner, 1:1 outer
Cardiolipin
Associated with many membrane complexes on inner mito membrane, essential for their proper function; 4 FA chains linked by Glycerol
Barth Syndrome
Mutation in Cardiolipin synthesis gene; Results in defective mito, cardiomyopathy, muscle weakness
Goal of Respiration
Reduce Oxygen to H20; Capture energy of electrons removed from Pyruvate
Function of Superoxide Dismutase
Eliminates Superoxide (O2-) by converting it to H202; Deficient in Lou Gehrig’s
What converts Superoxide to H2O2
Superoxide Dismutase
Function of Catalase
Convert H2O2 to oxygen and water; Found in mitochondria; Also found in RBCs
What converts H2O2 to oxygen and water
Catalase
What happens to H2O2 when Fe2+ is present?
Can react to form Hydroxyl Radical
What forms Hydroxyl Radical?
H2O2 reacting with Fe2+
What protects against Hydroxyl radicals
Vit C and E
Vit C and E
Protect against Hydroxyl Radicals
2 Functions of CAC
Electrons to ETC; Precursors for Biosynthesis
2 moeities on cytosolic side of Complex 3
Rieske Iron-Sulfur protein, Cytochrome C1
2 Regulatory components of PDH Complex
PDH Kinase and Phosphatase
3 Main Enzymes of PDH Complex
Pyruvate Decarboxylase E1, Dihdrolipoyl Transacetylase E2, Dihydrolipoyl Dehydrogenase E3
3 Postulates of Binding Change Mechanism
(1) Energy from H+ gradient used to release ATP; (2) 3 catalytic sites are each in unique conformation, conf’s are interconvertible, rep the 3 stages of catalytic cycle (L -> T -> O); (3) Conf changes at 3 sties are driven by rotation of gamma sub relative to F1 ball
4 Steps that produce NADH in CAC
Pyruvate DH, Isocitrate DH, A-KG DH, Malate DH
5 Cofactors for PDH Complex
TPP, FAD, NAD, CoA, Lipoic Acid
5 Sources of Acetyl CoA
Pyruvate (Glycolysis); AA Degradation; FA B-oxidation; KBs; Ethanol Metabolism
Alpha and Beta Subunits of ATP Synthase
Form the “Ball” of F1; Only beta has catalytic activity
Antimycin
Binds to N center on matrix side of Complex 3 (prevents e’s from reaching b hemes)
Aspartate/Malate Shuttle vs Glycerophosphate shuttle
NADH vs Ubiquinone Level
Branchpoint of Citrate in Mitochondria
(1) Can enter TCA Cycle; (2) exit through Citrate Shuttle to Export AcetylCoA for FA Synthesis; (3) Make alpha ketogluterate
CAC when Acetyl CoA high
Need for OAA; Pyruvate Decarboxylase stimulated (Pyruvate to OAA) and PDH inhibited; Shift from from oxidative to biosynthetic mode
Chemiosmotic Hypothesis
Inner membrane impermeable to H+, allowing gradient to be used for ATPase
Cofactor necessary for E1 Complex
Thiamin Pyrophosphate TPP (stabilize carbanion)
Cofactor necessary for E2 Complex
Lipoic Acid, Reacts w/ Carbanion intermediate from E1
Cofactor necessary for E3 Complex
?
Complex 2
Succinate DH; Tetramer; FAD and 3 Iron-Sulfur Clusters; Doesn’t pump protons
Complex 4
Cytochrome C oxidase; reduces O2 to H20; Proton pump; Redox centers
Complex I
NADH DH; 7 subunits in mito genome; Membrane and Peripheral Arm
Defect in Mitofilin
No contacts b/t Cristae and bounding Inner Membrane; Can’t export to Cytosol
Does FADH2 or NADH carry more energy?
NADH
E1 Reaction of PDH Complex
Decarboxylation of Pyruvate by E1; Produces unstable carbanion; Needs TPP
E2 Reaction of PDH Complex
Picks up Acetyl Group from TPP; Forms AcetylCoA
Elevator Model
Mutation of just 1 of 10-12 c subunits halts transport; Suggests subunit c rotates relative to a to form complete proton pathway
Energy made directly during TCA Cycle
1 GTP (Substrate-Level Phosphorylation)
Estimate for protons consumed per ATP synthesized
4
Fate of Pyruvate in TCA Cycle
Oxidized to 3 CO2 molecules
Findings of Noji experiment
Gamma subunit rotates
First place electrons go upon leaving cyt c
Copper A redox site of complex 4
First Ubiquinone binding site on Complex 3
Center P
Flavoproteins
Flavin gets electrons to pass to iron sulfur centers
Flow of electrons in Complex 2
Succinate -> FAD -> Iron-Sulfur Clusters -> Ubiquinone
FMN + AMP =
FAD
FMN in ETC
Cofactor bound to peripheral arm of Complex 1; Flavoprotein
How do electrons get to Complex 4
Cytochrome C carrier (one at a time)
How do oxygens reach active site of Complex 4?
Through lipid bilayer, not aqueous phase
How does Complex 4 compensate for adding electron to protein interior?
Take up a proton
How does structure change in Apoptotic Pathway
Extensive fusion of the Cristae precedes Cyt C release
How does the matrix appear in actively respirating mitochondria?
Condensed
How is NADH re-oxidized in aerobic conditions?
Passes electrons to ETC
How is NADH re-oxidized in anaerobic conditions?
Pyruvate is reduced to Lactate
How is Pyruvate imported into Mito Matrix?
Portin in Outer, Pyruvate Transport in Inner
How is the Intermembrane Space enlarged during Active Respiration?
Protons pumped in, and water follows
How many ATPs are made per complete revolute of gamma subunit relative to F1
3
How many e’s are needed to reduce oxygen?
4
How many protons are pumped at each complex?
4 at Complex 1; 4 at Complex 3; 2 at Complex 4 (per pair of e’s)
How many protons pumped per turn of Q cycle?
2
How many turns of Q cycle to fully reduce Ubiquinone?
2
How many turns of Q cycle to get 2 to Cytochrome C?
2, 1 per turn
How to Uncouple
Destroy proton gradient necessary for ox phosph (eg DNP)
Inhibitors of Isocitrate DH
ATP, NADH
Inhibitors of PDH Complex
Acetyl CoA, NADH, ATP (inhibitory phosphorylation)
Initial Reaction of PDH Complex
Decarboxylation of Pyruvate by E1; Produces unstable carbanion
Intermediate b/t NADH and Iron-Sulfur Center
Flavoprotein
Iron-Sulfer Clusters
Redox active centers that can accept and donate electrons; Conduit from FMN to Ubiquinone
Isocitrate Lyase
Cleaves isocitrate into Succinate and Glycoxylate
Main source of captured energy in TCA Cycle
NADH and FADH2
Malate Synthase
Adds Acetyl CoA to Glycoxylate to make Malate
Mito sn-Glycerophosphate DH
Part of Glycerophosphate shuttle for moving e’s from Cytosolic NADH into ETC
Most important anapleurotic rxn of CAC?
Pyruvate Carboxylase: Pyruvate -> OAA
Only ETC Complex that doesn’t pump protons
2, Succinate DH
Only membrane-bound enzyme in TCA cycle
Succinate Dehydrogenase
P/O Ratio
ATP Molecules produced per oxygen consumed, aka ATP produced/atom of oxygen
PEPCK
When OAA too high, coverts to PEP; uses one GTP
Problem with acetyl coA being precursor for FA biosynthesis
AcCoA made by PDH complex in mito, but FA synthesis occurs in cytosol
Purpose of E3 of PDH Complex
Removes electrons of sulfhydryls from Lipoic Acid; Forms NADH
Pyruvate Carboxylase
Pyruvate -> OAA; Can be used when not enough OAA for AcCoA
Pyruvate Dehydrogenase Action
Pyruvate to Acetyl CoA (irreversible)
Q Cycle
Ubiquinones at center P, one e to Rieske iron-sulfur and one to first b heme; e from Rieske to cytochrome c and e from heme to ubuiquinone at N center
Reaction mediated by Citrate Synthase
AcCoA + OAA -> Citrate (6C)
Redox centers of Complex 3
Two b type hemes in membrane subunit
Redox centers on Complex 4
2 Copper, 2 Hemes, Mg and Zn
Reduction Potentation of NADH/FADH2
Very high negative, tendency to move toward positive and release free energy
Role of Anconitase
Permits formation of A-KG
Rotenone Inhibitor
Binds to Complex 1 and Competes at Ubiquinone binding site (Electron transfer blocked)
Step that produces FADH2 in CAC
Succinate DH
Stigmatelin
Binds at P cener, the interface b/t iron-sulfur and cyt b (stops electron flow)
Stoichiometry of protons to electrons in ETC
4 protons/2 electonrs
T/F: The gamma subunit of ATP Synthase is symmetrical
False, different interactions with beta subunits around it
The addition of which enzyme joins the 2 halves of the CAC
A-KG Dehydrogenase
Two extra enzymes in Glycoxylate Cycle
Isocitrate Lyase and Malate Synthase
Ubiquinone
Lipid soluble e- carrier; Carries e’s b/t complexes in ETC; Can accept one at a time, but can carry 2
Ubiquinone Binding Sites at Complex 1
1 Tightly Bound, 1 Loose (transfer from Complex 1 to 3)
UCP2 protein
Exist in adult human tissue, could be turned on to uncouple and waste energy
Uncoupling
ETC and Oxygen reduction work, but not ox phosph (removal of F1)
What are the 2 reactions that make the TCA Cycle
AcetylCoA + OAA -> A-KG (forward); OAA -> SuccinylCoA (reverse, heme)
What can block the transfer of electrons from Complex 1 to 3
Rotenone
What converts Pyruvate to Acetyl CoA
Pyruvate Dehydrogenase
What did famous reconstitution experiment show?
No intermediate, just protone gradient could power ATP synthesis
What do flavoproteins carry e’s between?
Flavoproteins and Complex 3
What does Glycoxylation cycle bypass?
Decarboxylation steps of CAC
What does the Isocitrate Dehydrogenase enzyme produce?
Alpha-KG, CO2, NADH
What happens in too much OAA in CAC?
PEPCK converts it to PEP (costs one GTP)
What molecule from Glycolysis has to be imported into Mito Matrix for TCA?
Pyruvate
What parts still work when F1 part removed?
ETC and Oxygen reduction, but oxidative phosphorylation cannot
What prevents making sugar form fat in CAC?
Two decarboxylation steps; Acetyl CoA that enters is lost as CO2
What substrate in CAC is used for AA synthesis?
A-KG
What substrate in CAC is used for heme synthesis?
Succinyl CoA
Where does TCA cycle occur?
Mito Matrix
Which arm of Complex 1 contains all the redox active centers?
Peripheral
Which arm of Complex 1 contains the mito encoded subunits?
Membrane
Which Complex has channel for oxygen to reach active site?
Cytocrhome C Oxidase = Complex 4
Which complex has most mito coded subunits?
Complex 1
Which Complex hosts Q cycle
Complex 3
Which Complex of ETC contains Rieske Iron-Sulfur protein
Complex 3
Which complex reduces oxygen to water?
Complex 4 (cytochrome c oxidase)
Which E of PDH forms Acetyl CoA
E2
Which F is membrane part?
F_0
Which subunit forms the “axel” of F1
Gamma
Which subunit is identical b/t PDH and A-ketogluterate
E3
Which subunits form the rotor?
Subunit c, Epsilon, and Gamma
Which subunits form the stator?
a, b, alpha, beta, delta
Why do ETC complex proteins accept electons?
More positive reduction potential
Why is Succinate Dehydrogenase unusual in CAC?
Membrane bound and part of Complex 2
Why would A-KG leave the CAC?
AA synthesis, Glutamate
Why would OAA leave the CAC?
Aspartate
Why would we need to uncouple?
Allow electrons to flow in presence of high gradient
Yield from PDH Complex
1 Acetyl CoA and 1 NADH