Mitochondria & oxidative phosphorylation Flashcards
What is the full oxidation of glucose? In what circumstances does it occur?
How does the mitochondrion conserve energy?
What is the difference between the proton gradient and the proton motive force
- Glycolysis: 1 glucose -> 2 pyruvate
- In presence of O2, further oxidation of pyruvate by CAC.
Mitochondria conserve energy by being highly folded in the inner membrane. increases surface area to pump more H+ in intermembrane space, augmenting capacity to store energy through pmf.
Proton gradient: difference in proton (H⁺) concentration across a membrane. Consists of a higher concentration of protons on one side of the membrane (intermembrane space) compared to the other (mitochondrial matrix), creating a potential energy difference.
Pmf: electrochemical gradient that drives protons across the membrane. It is a measure of the potential energy stored in the gradient and includes both the concentration (proton) gradient (chemical potential) and the electrical potential (voltage difference) across the membrane
-drives ATP synthesis as protons follow their concentration gradient through ATP synthase
Describe the permability of the mitochondrial inner membrane (MIM) and mitochondrial outer membrane (MOM)
How does the mitochondrial pyruvate carrier (MPC) work?
What reaction happens with pyruvate once in the mitochondrial matrix? (+allosteric regulators)
MIM:
-impermeable to small molecules (except O2, CO2, H2O, HN3)
-contains respiratory chain
-contains transporters, such as the mitochondrial pyruvate transporter.
MOM:
-permeable to small molecules
MPC: symporter (transports 2 solutes in same direction) in MIM.
-selectively transports pyruvate (agaisnt its gradient) into matrix by tapping into H+ gradient energy source (following its gradient)
Once in matrix: oxidation of pyruvate
Pyruvate +NAD+ + CoA -> Acetyl-CoA + NADH + CO2
by pyruvate dehydrogenase complex (PDHC)
allosteric regulators: +pyruvate, +CoA, + NAD+, +ADP, +Ca2+, +Mg2+, -Acetyl-CoA, -NADH, -ATP
AcetylCoA goes to CAC, NADH goes to ETC.
Describe the TCA cycle.
Acetyl-Coa -> Citrate + CoA
-Citrate synthase
allosteric regulators: +insulin, +acetylCoA, +oxaloacetate,
-citrate, -NADH, -succinylCoA, -ATP
Citrate -> Isocitrate
-Aconitase
allosteric regulators: none
Isocitrate +NAD+ -> a-Ketoglutarate + NADH + CO2
-Isocitrate dehydrogenase
allosteric regulators: +ADP, +Ca2+, -NADH, -ATP
a-Ketoglutarate + CoA + NAD+ -> Succinyl-CoA + NADH + CO2
-a-Ketoglutarate dehydrogenase
allosteric regulators: +Cq+, -NADH, -succinylCoA, -ATP, -GTP
Succinyl-CoA + GDP + Pi -> Succinate + GTP + CoA
-Succinate thiokinase
allosteric regulators: none
Succinate + FAD -> Fumarate + FADH2
-Succinate dehydrogenase
allosteric regulators: none
Fumarate -> Malate
-Fumarase
allosteric regulators: none
Malate +NAD+ -> Oxaloacetate + NADH+
-Malate dehydrogenase
allosteric regulators: -NADH
Metabolic pathways converge on the CAC, pumping carbon into the cycle for 2 reasons. Which?
What does one turn of the CAC yield?
How is nutrition crucial in the proper operation of the CAC?
- Production of energy
- Generation of precursor molecules for biosynthetic pathways.
One turn yields
3 NADH, 1 FADH2, 1 ATP/GTP, 2 CO2.
CAC relies on minerals (Mn, Fe), cofactors (niacin (NAD), thiamin (TPP), panthothenic acid (CoA), biotin, flavin (FAD)), glucose (adenosine, contains ribose), and amino acids (protein biosynthesis of enzymes).
The CAC is an amphipoblic pathway. In what ways is it catabolic and anabolic?
How are AA involved in the CAC? (glucogenic, non-glucogenic)
What AA can generate
Acetyl-CoA
a-Ketoglutarate
SuccinylCoA
Fumarate
Oxaloacetate
Pyruvate
How does one metabolically go from citric acid to aspartate?
Central nature: CAC serves as platform for cell building reactions (anabolic)
Catabolic:
Degradation of acetyl-CoA, AA, ect.
Anabolic:
-Porphyrin rings (heme)
-FA (from citrate)
-Urea cycle (from fumarate)
-Glucose biosynthesis (gluconeogenesis)
AA can be converted into key intermediates of the CAC through transamination.
Alternatively, intermediates in the CAC can also regenerate AA
Glucogenic AA: can be converted into intermediates of the CAC that can be converted to glucose (Ex: pyruvate, oxaloacetate)
Non-glucogenic AA: cannot be converted to glucose, synthesize other compounds (AcetylCoA) for FA synthesis or ketone synthesis.
AcetylCoa: Alanine, Tryptophan, Methionine/Cysteine, Glycine, Serine, Threonine
a-Ketoglutarate: Glutamate
SuccinylCoA: Valine, Isoleucine, Methionine, Threonine, PROPRIONATE (SCFA from gut microbiome)
Fumarate: Asparagine, Phenylalanine/Threonine
Oxaloacetate: Asparagine, Aspartate
Pyruvate: Phenylalanine/Tyrosine, Tryptophan, Isoleucine
CAC from citrate -> oxaloacetate
oxaloacetate -> aspartate through transamination
How is acetylCoA a major metabolic intersection?
What are the non-glucogenic AA?
Describe the paths of citrate, oxaloacetate and alpha-ketoglutarate in different biosynthetic metabolic pathways
What is special about a-ketoglutarate? What about glutamate?
Glucose, FA and protein feed into acetylCoA, making in a major metabolic intersection.
-Glucose, through pyruvate, yields AcetylCoA
-FA, through beta-oxidation, yields AcetylCoA
-Proteins, through non-glucogenic AA yields AcetylCoA
-Non glucogenic AA: Lysine, Isoleucine, Leucine, Phenylalanine, Tyrosine, Threonine, Tryptophan
Oxaloacetate: under starved condition, yields malate, which exits the cell and is reconverted to oxaloacetate -> PEP for gluconeogenesis
*Can also yield citrate.
**Can also yield AA (asparagine and aspartate) and a-ketoglutarate
Citrate: under fed conditions, can yield acetyl-CoA for fatty acid synthesis (lipogenesis).
a-ketoglutarate: can yield AA (glutamate, which then yields glutamine, proline, arginine)
a-ketoglutarate: main reservoir for ammonia
glutamate: key for production of other AA.
What is chemiosmotic theory?
Describe it.
Chemiosmotic theory: explains how ATP is produced in cells through the electron transport chain.
Complex 1:
NADH -> NAD+ (returns to CAC)
Electrons move to FMN, to multiple Fe-S clusters, to next electron carrier in C2.
Pumps 4H+
Complex 2: Succinate dehydrogenase
FADH2 -> FAD (returns to CAC)
Electrons move from Fe-S clusters in C1 to those in C2 to CoQ10.
CoQ10 moves to C3.
Complex 3:
Electrons move from CoQ10 to Cytochrome C, Fe-S clusters.
Pumps 4H+
Complex 4:
Cytochrome C arrives are releases electrons, which reach oxygen.
Pumps 2H+
Complex 5: ATP synthase
Couples H+ import to ADP to yield ATP.
Which minerals ensure succesful electron transfer? Where are they located in the ETC?
What is CoQ10?
How is it made in the body?
How can statins affect CoQ10 synthesis?
How can consequences be mitigated?
How is impaired CoQ10 biosynthesis linked to neurological damage?
Heme: porphyric ring (made from CAC) with central Fe
-involved in cytochrome for electron transfer
Fe-S clusters: configurations of Fe-S atoms
-involved in C1, C2 and C3 for electron transfer
CoQ10: ubiquinone, principal electron acceptor and donor from C1 and C2 to C3 in ETC.
-antioxidant: can quench lipid radicals from lipid peroxidation.
CoQ10: synthesized from mevalonate
Statins: used to treat familial hypercholsterolemia by inhibiting HMGR reductase in cholesterogenesis, which converts HMGCoA to mevalonate.
Reduced mevalonate, means for less CoQ10 production, and less antioxidant protection and impaired ETC. (linked to neurological damage)
Supplementation: when ingesting statins, use CoQ10 supplement.
Mitochondria-targeted CoQ10 (MitoQ) is a CoQ10 tagged with triphenol, allowing it to selectively accumulate in mitochondria (lipophilic cation in phenols attracted to negative inside of mitochondria)
Link to neurological damage: less CoQ10 means more ROS induced damage and less ATP production, which impairs energy-demanding tissues like the brain.
What is respiration uncoupling?
What do uncouplers do? Example (3)
What are the effects of uncoupling?
What does UCP-1 do?
Respiration uncoupling: Disruption of coupling between ATP synthesis and ETC, more specifically, disruption of creation of proton gradient.
**Aspirin is an example of an uncoupler.
DNP is an example of an uncoupling agent
UCP-1 (thermogenin) is a proton channel protein that acts as a uncoupling agent.
An uncoupler carries H+ across MIM, without it needing to pass with ATP synthase.
-energy usually used to produce ATP produces heat instead
-ATP synthesis is decreased
UCP-1: uncoupling agent that translocates H+ across the MIM to generate heat. (Brown adipose tissue uses UCP-1 for thermogenesis in cold environments).
Why is it important to know how mitochondria work?
What does mitochondrial nutrient metabolism depend on?
How can mitochondrial metabolic efficiency be measured? With what method can this be done?
Mitochondria are hubs for nutrient metabolism and energy homeostasis: conversion of fuels into intermediates required for ATP production and cell building reactions.
Depends on succesful transfer of electrons from fuels to terminal electron acceptor (O2).
By observing O2 saturation. With the test for mitochondrial dysfunction, observing the states of respiration.
What does mitochondrial dysfunction testing measure?
What are the steps in testing mitochondrial dysfunction?
Test: measures oxygen consumption of mitochondria in the goal of understanding disease pathogenesis
-Measures oxygen saturation over time in different states of respiration.
Testing mitochondrial dysfunction:
State 1: Mitochondria with no buffer = no respiration.
State 2: Addition of substrate in chamber to commence respiration
-Oxidation of NADH as electrons move through ETC.
-Lack of ADP = no return of H+ through ATP synthase = low respiration.
State 3: Addition of ADP in chamber to complete proton circuit.
-Exportation of protons
-High respiration
-Oxygen consumption levels out upon exhaustion of ADP.
State 4: Addition of oligomycin in chamber.
-Interference with complex 5 by inhibiting it.
-Respiration slows down
Addition of uncoupler: FCCP bypasses C5 and returns H+ through MIM, completing the proton circuit.
-High respiration
State 5: Addition of antimycin A in chamber.
-Arrests complex 3 to halt electron flow in ETC.
-Ensures researchers that oxygen consumption that took place was truly due to the proper functioning of the ETC.
-Respiration stops
