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BioChem: TCA Cycle


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How do aerobes generate energy?
-by using oxygen through:
-tricarboxylic acid cycle (TCA)
-Electron transport chain
-oxidative phosphorylation
What catalyzes the reaction of pyruvate entering the TCA cycle?
-Pyruvate Dehydrogenase
Describe Pyruvate Dehydrogenase
-contains three different activities
-uses five different coenzymes
-huge complex 4.6 million Da
(24 polypeptides of 1, 24 of 2, and 12 of 3)
What are the three different activities performed by Pyruvate Deyhydrogenase?
-pyruvate dexarboxylase OR pyruvate dehydrogenase
-dihydrolipoamide transacetylase
-dihydrolipoamide dehydrogenase
Pyruvate Dexarboylase uses what?
And what does dihydrolipoamide transacetylase use?
-thyamine pyrophosphate
-lipoic acid
What do Flavoproteins use Flavin Coenzymes as?
-Electron Carriers
What does reaction 1 do in the TCA cycle?
-introduces 2 carbons
What is known as a suicide substrate?
What does reaction 2 do in the TCA cycle?
-isomerization of citrate
Citrate is symmetrical, but what treats is asymmetrically?
What happens in reaction 3 in the TCA cycle?
-Oxidation of Isocitrate
What happens in reaction 4 in the TCA cycle?
-oxidation of alpha-ketoglutarate
What happens in reaction 5 in the TCA cycle?
-cleavage of Succinyl-CoA
What happens in reaction 6 in the TCA cycle?
-Oxidation of succinate
What happens in reaction 7 in the TCA cycle?
-hydration of fumarate
What occurs in reaction 8 of the TCA cycle?
-oxidation of malate
What are the highest energy yields developed from the TCA cycle?
-Isocitrate DH
-Ketoglutarate DH
-Malate DH
What is the lowest energy yielding reaction from the TCA cycle?
How about the middle energy yield?
-Succinyl-CoA Synthase
-succinate DH
What are the two problems with the TCA cycle?
1) How to get pyruvate into the mitochondria
2) How to get reducing power (NADH) into the mitochondria
What are two other functions of the TCA cycle?
-most important energy generating process in the cell
-TCA intermediates are starting materials for other important molecules in the cell
Why must the TCA cycle be tightly controlled?
-it is the link between Glycolysis and the Electron Transport Chain
How many sites are there for TCA control?
What has the order from greatest free energy (-43.9) of TCA reactions to least (0.8)?
-Citrate synthase > Alpha Ketoglutarate DH > Isocitrate DH > Malate DH, Fumarase, Succinate DH, Succinyl CoA Synthase > Aconitase
Animals can not synthsize sugars from what?
What can some bacteria use as their only carbon source?
What type of seeds can grow with only stored fats?
-oil seed plants
What are some symptoms of Pyruvate Dehydrogenase Deficiency?
-children with pyruvate DH deficiency have elevated serum lactate, pyruvate, and alanine
-neurological defects
-treatment with dichloroacetate, inhibitor of Pyruvate DH kinase
What are some symptoms of Fumarase Deficiency?
-urine contains elevated amounts of fumarate, succinate, ketoglutarate, and citrate
-sufferers have severe neurological impairment and sydtionia developing soon after birth
What are two diseases of the TCA cycle.
-Pyruvate Dehydrogenase Deficiency
-Fumarase Deficiency
How can you make a table of Standard reduction potentials?
-by using the standard hydrogen electrode
What can the data from the half reactions be used for?
-analyzing energy changes in redox reaction
How do spontaneous reactions work?
-electrons from the more negative reduction potential half-reaction are donated to the half-reaction with the more positive reduction potential

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