Deevska-Block 2 Flashcards
Where is pyruvate oxidiized to acetyl CoA?
Mitochondrial matrix
What molecules are produced in the TCA cycle?
-3 NADH
-1 FADH
1 GTP
How is glycolysis and TCA linked?
Pyruvate is the end product of glycolysis which goes to the TCA cycle. PDH converts it to acetyl Coa, which combines with oxaloacetate to form citrate (with enzyme citrate synthase) to go into the actual cycle
Explain the function and structure of the PDH complex
- 3 separate enzymes (E1, E2, E3)
- 5 different cofactors
- TPP
- lipoamide
- CoA
- FAD
- NAD
What are the cofactors of PDH?
- TPP
- lipoamide
- CoA
- FAD
- NAD
What activates PDH?
- dephosphoryaltion
- pyruvate
- NAD+
- ADP
- Ca2+
- CoA
What deactivates PDH>?
- acetyl CoA
- NADH
- ATP
- phosphorylation
PDH and deficiency of niacin or thiamine
Can cause serious CNS problems
Arsenic poisoning
Males lipoic acid unavailable as coenzyme for PDH
Sequence of reactions in TCA
- Synthesis of citrate from acetyl CoA and oxaloacetate (citrate synthase)
- Isomerization of citrate to isocitrate (aconitase)
- Oxidative decarboxylation of isocitrate to a-ketoglutarate (isocitrate dehydrogenase)
- Oxidative decarboxylation of a-ketoglutarate to succinyl CoA (a-ketoglutarate dehydrogenase complex)
- Cleavage of succinyl CoA to Succinate (succinyl CoA synthetase or succinate thiokinase)
- Oxidation of succinate to fumarate (succinate dehydrogeanse)
- Hydration of fumarate to malate (fumarase)
- 1 oxidation of malate to regenerate oxaloacetate and produce NADH + H+ (malate dehydrogenase)
Identify the 4 oxidative enzymes in the TCA cycle, their products, and regulation
PDH
- product is acetyl CoA
- activated by: pyruvate, NAD+, ADP, Ca2+, CoA, dephosphorylation
- deactivated by acetyl CoA, NADH, ATP, phosphorylation
Isocitrate dehydrogenase
- product is a-ketoglutarate
- inhibited by: ATP, NADH
- activated by: ADP, Ca2+
A-ketoglutarate dehydrogenase
- product succinyl CoA
- inhibited by: products
- activated by Ca2+
Succinate dehydrogenase
-product: fumarate
What are the 4 oxidative enzymes of the TCA?
- PDH
- isocitrate dehydrogenase
- a-ketoglutarate dehydrogenase
- succinate dehydrogenase
Identify the 2 intermediates required in the first step of the TCA cycle and their metabolic sources.
- OAA and pyruvate
- pyruvate comes from glycolysis as the end product and is changed into acetyl CoA via PDH
- OAA is just cycled through TCA over and over again
Identify 4 important products synthesized from the TCA cycle and summarize the energy yield for 1 glucose molecule
- 2 CO2
- 3 NADH
- 2 FADH
- 1 GTP
- 36-38 ATP overall
Identify the enzymes from the TCA cycle affected by vitamin deficiency and arsenic poisoning and explain the underlying reason for that.
Enzymes: PDH and A-ketoglutarate
- arsenic poisoning forms a stable theology bond with lipoic acid (coenyme for both enzymes) making it unavailable to be used as a coenzyme
- affects the brain causing neurological disturbance and death
Why don’t we get glucose from TCA?
Because PDH is irreversible, we don’t have enzymes to catalyze the reverse reaction
Outline the structure of the mitochondria and the mitochondrial electron transport system showing all major electron carriers.
- electron carriers: NAD+ and FAD
- outer membrane: permeable to most ions and small molecules
- innermembrane: impermeable to most small ions and large molecules
- Matrix: TCA cycle enzymes, FA oxidation enzymes, mitochondrial ribosomes
Electron transport assembly
Complex 1-NADH dehydrogenase
- FMN
- iron sulfer center
Complex II - succinate dehydrogenase
- only one embedded in the inner mitochondrial membrane
- FAD contains iron sulphur center
CoQ
- ONLY nonprotein carrier
- quinine derivative
Complex III-cyt b and c1
-heme group which reversible converted from ferric to ferrous
Complex IV-cyt a and a3
- heme group which reversible converted from ferric to ferrous
- Cu
- heme directly reacts with O2
Cyt c
-freely moving in the intermembrane space
Complex V-ATP synthase
-multisubunit
Describe how the TCA cycle is regulated by substrate supply, allosteric effectors, covalent modification, and protein synthesis
PDH covalent modifications:
-phosphorylation deactivates
-dephosphorylation activates
-PDH kinase and phosphatase can be allosterically activated or inhibited by substrate activation and product inhibition
Other regulations:
-activation: pyruvate, NAD+, ADP, Ca2+, CoA
-deactivation: acetyl CoA, NADH, ATP
Isocitrate dehydrogenase allosteric regulation
- inhibitors: ATP and NADH
- Activators: ADP and Ca2+
A-ketoglutarate dehydrogenase regulation
- inhibitors: its products
- activators: Ca2+
Explain the role of uncoupling proteins in thermogensis
- allow H+ to flow back into the matrix without passing though complex V, and not forming ATP
- the free energy is released as heat (nonshivering thermogenesis)
- UCP1 (thermogenin) found in brown fat
Give examples of synthetic uncouplers (such as salicylic acid) and their effect on the ETC
- 2,4-dinitrophenol: used as a weight loss drug in the 30s. However its use was banned because it was relatively easy to overdose, which can cause a fatal hyperthermia, although its use still persists (illegally)
- compounds containing salicylic acid will also cause uncoupling, including aspirin. Overdoses of aspirin will cause a high fever and profuse sweating, and can be potentially fatal
Describe the effects of inhibitors such as rotenone, antimycin A, carbon monoxide, cyanide and oligomycin on oxygen uptake by mitochondria and ETC function
- Amytal: complex I-barbiturate. Importance of proper drug dosage
- Rotenone: complex I-insecticide, piscicide, and pesticide
- antimycin A: complex III-pesticide
- CN-complex IV-irreversibly binds to the Fe3+ in the heme group of cyt c-oxidase
- CO-complex IV-binds irreversibly- tight binding to hemoglobin
- NaN3-binds similarly to CN to the Fe3+ of iron in cyt
- oligomycin-binds to the F0 domain closing the proton channel leading back into the matrix and shutting down ATP synthesis
Describe the role of mitochondria in apoptosis.
- initiated through mitochondria intrinsic pathways resulting in the formation of pores in the outer mitochondrial membrane
- pores allow cyt C to be released in the cytosol
- capsases cause cleavage of key proteins that result in the morphological and biochemical changes characteristic of apoptosis.
What disease can result from mutations in the mtDNA or nuclear DNA?
- LHON
- mycolonic epilepsy with ragged red fibers (MERRF)
- mitochondrial encephalomyopathy, lactic acidosis, and stroke like episodes (MELAS)
- Leigh syndrome