BioChem: TCA cycle 2

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What does the fate of Pyruvate depend on?: -cell energy charge
If cell energy charge is low, what happens to pyruvate? How about high?: -oxidized to CO2 and H2O in the TCA cycle
-directed toward gluconeogenesis
Where does the enzymatic activities of the TCA cycle occur?: -mitochondrion
How is pyruvate directed toward gluconeogeneis when cell energy charge is high?: -CoA is highly acylated (as acetyl-CoA)
-it allosterically activates pyruvate carboxylase which directs towards gluconeo.
How is pyruvate directed toward the TCA cycle when cell energy charge is low?: -CoA NOT acylated
-pyruvate carboxylase remains inactive
-pyruvate can then be metabolized via the PDH complex
What are the 5 coenzymes used in the PDH cycle?: -CoA
-NAD+
-FAD+
-lipoic acid
-thimaine pyrophosphate (TPP)
Which coenzymes are tightly bound to enzymes of PDH complex?: -TPP
-lipoic acid
-FAD+
Which coenzymes are employed as carriers of products of the PDH cycle?: -CoA
-NAD+
What does PDH stand for and what role does it play in the TCA cycle?: -Pyruvate Dehydrogenase
-oxidatively decarboxylates pyruvate so it can bind to TPP
What is the end result of the PDH complex and why is this important?: -Acetyl-CoA
-this acts as regulation of the TCA cycle
How is Fluoroacetate a suicide substrate? What is the purpose of this?: -It becomes Citrate Synthase which then becomes Fluorocitrate
-this inhibits aconitase which blocks the TCA cycle
How many moles of ATP are generated from one mole pyruvate that enters the TCA cycle? Give the breakdown of where the ATP comes from.: -12 ATP
*3 mol NADH (1 mol is equal to 3 mol ATP) plus 1 mol FADH2 (1 mol equal to 2 ATP) plus 1 GTP (equal to 1 ATP)
Biosynthetically speaking, why is the TCA cycle important?: -Each intermediate is important for other processes
Biosynthetically, what is Actyl-CoA used for? Alpha-ketoglutarate? Succinyl CoA? Oxaloacetate?: -FA terpenoids
-AA
-Porphyrins
-Carb AA
What two cycles does the TCA cycle link?: -glycolysis
-electron transport chain
Where is the TCA cycle regulated?: -entry of Acetyl-CoA into cycle
-Isocitrate to alpha-ketoglutarate
-alpha-ketoglutarate to succinyl-CoA
How is the first regulation site controlled?: -high concenctrations of Succinyl-CoA and citrate act as allosteric inhibitors of citrate synthase stopping the conversion of citrate from OOA and Acetyl-CoA
How is the second regulation controlled?: -high concentrations of NADH and ATP inhibit cycle and therefor citrate synthesis (since this is a reversible reaction)
How is the last regulation site controlled?: -Succinyl-CoA and NADH inhibit formation of more Succinyl-CoA
Overall, what affects PDH activity?: -Its state of phosphorylation (most active in dephosphorylated state)
What catalyzes phosphorylation of PDH and what effect does this have?: -PDH kinase
-makes PDH less active since it is more phosphorylated
What enhances PDH kinase (and therefore phosphorylates PDH making it less active)?: -high cellular charge which is indicated by increase in ATP, NADH, and aceyl-CoA.
What inhibits PDH kinase?: -increase in pyruvate
-ADP, NAD+, and CoASH
How is PDH phosphatase activated?: -Mg2+ and Ca2+
In adipose tissue, what increases PDH activity? How about in cardiac muscle?: -insulin
-catecholamines
What cycle is used in comparison to the TCA cyle in plants, some fungi, algae, protozoans, and bacteria?: -Glyoxylate cycle
Where does the glyoxylate cycle occur?: -in glyoxysomes
What is the purpose of the glyoxylate cycle?: -using two carbon compounds (such as ethanol, acetate, and acetyl-CoA from FA) things can survive in the absence of photosynthesis by producing precursers of glucose.
What are the intermediates of the glyoxylate cycle?: -acetyl-CoA enters and becomes citrate
-then isocitrate
-then glyoxylate (and succinate)
-then malate
-then oxaloacetate
*repeats
What are some diseases of the TCA cycle?: -Pyruvate Dehydrogenase Deficiency
-Fumarase Deficiency
Describe Pyruvate Dehydrogenase Deficiency: -children have elevated serum lactate, pyruvate, and alanine
-neurological defects
-treatment with dichloroacetate, inhibitor of pyruvate DH kinase
Describe Fumarase Deficiancy: -rare
-urine contains elevated amounts of fumarate, succinate, ?-ketoglutarate, and citrate
-severe neurological impairment and dystionia soon after birth
What are redox reactions composed of?: -two half reactions which can be separated
How can the energy change in a redox reaction be found?: -separate reactions using table
-find potentials
-plug into: change= acceptor - donor
*donor has more negative potential so answer is positive

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