TCA cycle Flashcards
(34 cards)
What are the three main things to follow when going through the TCA cycle rxns?
-# of carbons and where they are
-movement of electrons
-follow the energy (delta G)
How many reactions are there in TCA cycle?
8 reactions
What is the output from 1 acetyl-CoA?
-2 CO2
-1 ATP
-3NADH/H+
-1 FADH2
Roughly how much ATP is 1 NADH equivalent to?
~2.5 ATP = 1 NADH
roughly how much ATP is 1 FADH equivalent to?
~1.5 ATP = 1 FADH
What is a metabolon?
-group of enzymes performing reactions with a common function
-these enzymes can be localized in organelle or part of organelle
-seen in glycolysis, gluconeogen, FA synth, and ETC
What is substrate channeling?
-when the product of one rxn directly becomes the substrate for the next rxn
-used for small molecules (1-2C)
-uses biological tethers
-ex. Co-A in acetyl-CoA
What is important about Acetyl-CoA?
-important intermediate
-product of pyruvate oxidation
-product of fatty acid metabolism
-chemical bonds are energetically rich
-carries 2C acetyl group
Step 1: citrate synthase
-condensation synthesis
-acetyl-coA (2C) + oxaloacetate (4C) -> citrate (6C)
-irreversible
-favourable rxn
Step 2: Aconitase
-isomerization (sort of) = two steps of dehydration then hydration
-citrate (6C) -> isocitrate (6C)
-reversible
-near 0 G
What is the intermediate for the two step reaction of aconitase enzyme?
cis-Aconitate
Step 3: Isocitrate Dehydrogenase
-oxidation decarboxylation
-isocitrate (6C)-> a-ketoglutarate (5C) + CO2
-produces NADH/H+
-irreversible
-favourable rxn
Step 4: a-ketoglutarate dehydrogenase
-oxidation decarboxylation
-a-ketoglutarate (5) -> succinyl-CoA (4) + CO2
-NADH/H+ produced
-irreversible -> Rate Limiting
-very favourable reaction
What are the parts of the a-ketoglutarate dehydrogenase complex?
-multienzyme
-E1 = TPP decarboxylase
-E2 = dihydrolipoyl transferase
-E3 = dihidyrolipoyl dehydrogenase
Of the carbons lost in the first 4 steps of TCA, are they from the acetyl CoA or the oxaloacetate?
-they are from the oxaloacetate
-still have both C from the acetyl CoA
Step 5: Succinyl CoA Synthase
-substrate-level phosphorylation
-succinyl-CoA (4C) -> succinate (4)
-1 ATP produced via water
-reversible rxn
-near 0 G
Step 6: Succinate Dehydrogenase
-oxidation
-succinate -> fumarate
-produces an FADH2
-reversible
-near 0 G
What is fumarate?
a trans-dioic acid
What is important about succinate dehydrogenase enzyme?
-bound to mito inner membrane
-part of Complex 2 in ETC
-near equilibrium = reversible
-FAD covalently bound
-uses FADH2 to reduce alkane to alkene because potential too low for NAD+
Step 7: Fumarase
-hydration
-fumarate (4C) + water -> malate (4C)
- reversible
-energy not used or produced
-near 0 G
Step 8: Malate Dehydrogenase
-oxidation
-Malate (4C) -> oxaloacetate (4C)
-reversible
-makes NADH/H+
-near 0 G = driven forward by product removal
Which steps of TCA are irreversible?
step 1, 3, 4
Which steps of TCA are reversible?
steps 2, 5, 6, 7, 8
Which steps produce NADH?
steps 3, 4, 8
