TCA cycle Flashcards
wk 7
How are kinase and phosphatase regulated?
Via changes in NADH, acetyl-CoA, pyruvate and Insulin.
How is the pyruvate dehydrogenase complex regulated?
Covalent modification using specific kinase and phosphatase
What is covalent modifcation?
Where the structure of an enzyme is modified by adding special groups to specific locations. In regulation - the addition of these groups is reversible.
What are the cofactors used in the regulation of pyruvate dehydrogenase
Thiamine, Lipoate and FAD+
What are the activator Allosteric regulators of pyruvate Dehydrogenase?
F1,6BP
What are the inhibitory Allosteric regulators of pyruvate Dehydrogenase?
ACoA
NADH
What are the consequnces of pyruvate Dehydrogenase deficiency?
- Progressive neurodegenerative disease
- Intermittent ataxia
- Poor muscle tone
- Lethargy
- Seizures
- Abnormal eye movements
- Lactate buildup
What are the intermediates of the TCA cycle?
Citrate
Isocitrate
A-ketoglutarate
Succinate
Fumarate
Malate
Oxaloacetate
What is the role of anaplerotic reactions
replenishes oxaloacetate in the citric acid cycle after been consumed AND maintain adequate levels of ATP to allow for the uninterrupted continuation of cellular respiration.
What are anaplerotic reactions?
Chemical reactions that form the intermediates for the TCA cycle.
What is the chemical make-up of Oxaloacetate?
an Asparate transaminase
What is the only mitochondrial enzyme capable of ATP production and how?
Syccinyl-CoA Synthetase
via substrate level phosphorylation (anaerobic)
What is the role of Syccinyl-CoA Synthetase?
conversion of Succinyl CoA –> Succinate
What is Cataplerotic vs anaplerotic
C= exit point
A = Entry points
What occurs when there is high ADP?
Faster respiration
What occurs when there is low ADP?
Slower respiration
How is the rate of respiration controlled?
By the amount of ADP
What does electron flow cause?
transport of protons from mitochondrial matrix into inner membrane
What does the electron transport chain create?
proton concentration gradient
What is chemiosmosis?
Process of ATP synthesis using free energy from electrons when they are passed to several carriers
How does the TCA cycle link to glucose oxidation and ATP production?
Link reaction connects glycolysis to TCA by creating aCoA
Electron transporters used to generate a proton motive force and generate ATP via chemiosmosis
Oxidative phosphorylation
What are the 5 major exit points of the TCA cycle?
Citrate, Ketogluctarate, Succinyl CoA, Malate and OAA
What are the 5 major entry points (anaplerotic reactions)
Ketoglutarate, succinyl-CoA, Fumarte, malate and OAA
What is the linking reaction in the TCA cycle?
Pyruvate + CoASH + NAD –> CoA + NADH2 + CO2
(occurs twice)
Where does the linking reaction occur?
Mitochondrial matrix
How is the linking reaction regulated?
Via Allosteric activity and inhibition
What are the components that are allosterically activated involved in linking reaction regulation?
NAD+, ADP, Pyruvate, CoASH and Ca
How are active allosteric enzymes activated?
by dephosphorylation
What are the allosteric inhibitors involved in regulation of linking reaction?
NADH2, acetyl CoA and ATP
How are allosterically inhibited components inhibted?
via phosphorylation
What steps in the TCA cycle are regulated?
Citrate Synthase, Aconitase, Isocitrate DH, a-KG DH, Succinate DH and malate DH
How is citrate synthase regulated?
allosterically activated by citrate.
How is aconite regulated?
inhibited by fluroacetate
How is Isocitrate DH regulated?
Allosteric activated: ADP, NAD, CA
Allosteric inhibited: ATP, NADH2 and Succinyl CoA
How is a-KG DH regulated?
Allosteric activated: ADP, NAD, CA
Allosteric inhibited: ATP, NADH2 and Succinyl CoA
How is Succinate DH regulated?
Inhibited by malonate (competitive inhibitor)
What is the purpose of the ETC?
recycle NADH2 and FADH2 into NAD+ and FAD+
What is the site of reactions in the ETC?
transmembrane proteins in the inner mitochondria membrane
what are the two entry reactions to the ETC?
1- NADH2 at complex 1
(NADH-Q reductase) (oxidised to NADH+)
2- FADH2 at complex 2
succinate DH) (oxidised to FAD)
What are the 4 large protein complexes for ETC?
I = NADH-Q Reductase
II- Succinate Dehydrogenase
III - Cytochrome C Reductase
IV- cytochrome c Oxidase
What is the first step in the electron transport chain? (electron movement)
NADH2 oxidised at complex I
What is the second step in the electron transport chain? (electron movement)
Complex I transfers electrons to CoQ
What is the third step in the electron transport chain? (electron movement)
FADH2 oxidised to FAD+ at complex II
What is the fourth step in the electron transport chain? (electron movement)
electrons are transferred from CoQ –> cytochrome c –> complex IV
What is the fifth step in the electron transport chain? (electron movement)
O2 reduced at complex IV
What are the four steps that allow the ETC to produce ATP?
- electron flow causes complexes I-IV to pump protons into intermembrane space
- proton movement creates a proton gradient across the inner mitochondrial membrane
- protons diffuse down the gradient through an ATP synthase channel
- ATP synthase catalyses ATP synthesis
How many ATPs synthesised per NADH2?
pumps 10 protons = 4 protrons per ATP = 2.5 ATP
What is meant by coupling?
the electrochemical gradient couples the rate of ETC with the rate of ATP synthesis
How many ATPS synthesised per FADH2?
pumps 6 protons (4 protons per ATP) = 1.5 ATPs
What is uncoupling?
ATP synthesises and electron flow is disconnected
electron transport no longer regulated by intact chemiosmotic gradient
Where do protons come from?
ADP-ATP translocate, H+ pyruvate symporter, shuttles, fatty acid oxidation, NADH2 and FADH@ oxidation and water
How does ATP:ADP affect the rate of ETC?
decreased ADP:ATP slows down the rate
Increased: speeds it up
What are the consequences of uncoupling?
increased ADP:ATP = increased electron flow = O2 consumption
increased heat production as energy stored in proton gradient is released.
ATP use greater than formation = metabolic acidosis with compensatory respiratory alkalosis
How does ATP affect ATP synthesis?
Respiratory Rate Determines avaliability of O2
What is the effect of dinitrophenol?
dissipates proton gradient by transporting protons across inner mitochondrial membrane via simple diffusion-mediated transport
What is the effect of thermogenin?
promotes heat generation (non-shivering thermogenesis)
What is thermogenic?
Physiological uncoupler (in brown fat)
What is the main (general) action of ETC inhibitors?
Prevent electrons from being passed from 1 carrier to the next
What are the ETC inhibitors?
Antimycin
Cyanide and carbon monoxide
ogliomycin
atratyloside
rotenone
What is the effect of antimycin?
Inhibits the electron transfer from III to Cytochrome C
Inhibits NADH2/FADH2 dependent O use
inhibits ATP synthase
What is the effect of cyanide and carbon monoxide?
prevents the docking of O2
Inhibits complex IV
Inhibits ATP synthesis
What is the effect of oligomycin?
Inhibits proton passage through ATP synthase –> proton concentration acts as a barrier to the export of more proteins = decreased electron flow
What is the effect of atractyloside?
Blocks ADP-ATP transolcase
Cytosolic protons accumulation arrest the ETC
inhibits O2 Consumption
What is the effect of Roteone?
Inhibits electron transfer from I to CoQ
Restricts NADH2 oxidation
inhibits generation of proton gradient, O2 consumption and ATP synthesis
In the TCA cycle, how many ATPS are produced per glucose?
32
How do cells produce energy in the absence of oxygen?
Using lactic acid fermentation (glycolysis alone)
What happens to the pyruvate in glycloysis in aerobic conditions?
it is converted to acetyl CoA –> enters the TCA –> electrons enter ETC
What happens to the pyruvate in glycolysis under anaerobic conditions?
Converted into lactate then enters the Cori cycle
What does AMPK mean?
AMP- activated protein kinase - used to regulate cellular metabolism.
What is the role of AMPK in regulation?
- Shuts off anabolic pathways (ATP using)
- Turns on catabolic pathways (ATP making)
What factors activate the regulator: AMPK?
increased ADP:ATP
increased AMP:ATP
What is the mechanism of action for metformin?
inhibits complex I → decreased NADH2 oxidation → decreases proton-driven ATP synthesis → increases ADP:ATP and increases AMP:ATP → inhibits glucagon-induced cAMP synthesis and activates AMPK
What are the actions of metformin in glycolysis?
increased glucose uptake
increased glucose
transporter translocation
increase insulin receptor activity
increase insulin-mediate glucose uptake in skeletal muscle
stimulates glycolytic enzymes
What is the role of gluconeogenesis?
- $\downarrow$ uptake of gluconeogenic substrates (alanine, lactate)
- inhibits gluconeogenic enzymes
- enhances insulin-mediated suppression of gluconeogenesis
- opposes the gluconeogenic action of glucagon
What does ETC do to NADH2 and FADH2?
recycles it back to NAD and FAD
What happens to the energy in the ETC?
As the electrons are transported along the chain, they lose energy. Some of this energy is conserved by forming a proton gradient in the inner mitochondrial membrane
Where does cytochrome carry electrons to?
complex IV
What carrier picks up electrons from complexes I and II and where does it take them?
Ubiquinone Q, takes them to Complex III
what does dinitrophenol do?
dissipates proton gradient via transport of protons across inner mitochondrial membrane
increased CHO and lipid metabolism
What are the ETC inhibitors?
Antimycin
cyanide and carrbon monoxide
oligomycin
atractyloside
rotenone
