19. CAC cycle Flashcards
how many steps are there in the CAC
8
how many of the 8 steps of the CAC are oxidations
4
what form is the energy in that is released from the CAC
reduced electron carriers: NADH or FADH2
step 1: what are the reagents and how many carbons are they
acetyl-CoA (2C) and OAA (4C)
step 1: what do acetyl CoA and OAA join to produce + what type of reaction is this
citrate (6C)
claisen condensation
step 1: what enzyme is used
citrate synthase
step 1: what happens to the free CoA
it can return to the PDH complex
step 1: describe the delta G’o
large and negative
step 1: describe how acetyl CoA and OAA are joined
the methyl of acetyl CoA is joined to the carbonyl carbon of OAA
step 1: other than the enzyme, what is over the arrow
H2O converting to CoA-SH
step 1: describe the structure of citrate synthase
homodimer, one domain is flexible in each subunit and undergoes a conf. change upon OAA binding. This exposes the binding site for acetyl CoA
step 1: reversible or irreversible
irreversible
step 2: what is the reagent and product
citrate into isocitrate
step 2: reversible or irreversible
reversible
step 2: what is the intermediate produced
cis-aconitate
step 2: what enzyme is used
aconitase
step 2: T or F; the enzyme aconitase is used for both halves of the reaction
true
step 2: what type of reaction is this
dehydration, then rehydration. The OH group of citrate gets repositioned to isocitrate
step 3: what is the reagent and product
isocitrate into a-ketoglutarate
step 3a: what does isocitrate first convert to
oxalosuccinate
step 3a: what enzyme converts isocitrate to oxalosuccinate
isocitrate dehydrogenase
step 3a: what goes over the arrow
NAD(P)+ –> NAD(P)H + H+
step 3a: what kind of reaction is this
oxidation
step 3b: what does oxalosuccinate convert to
an intermediate
step 3b: what goes over the arrow
loss of CO2
step 3b: what type of reaction is this
decarboxylation
step 3c: what does the intermediate convert to
a-ketoglutarate
step 3c: what type of reaction is this
rearrangement
step 3: overall, what type of reaction is the conversion of isocitrate to a-ketoglutarate
oxidative decarboxylation (via loss of CO2)
step 3: overall, what happens to electron carriers
carriers get reduced by the electrons from the oxidation
step 3: what amino acid is a-ketoglutarate the a-keto acid of
glutamate
step 4: reagent and product?
a-ketoglutarate into succinyl-CoA
step 4: what type of reaction is this
oxidative decarboxylation
step 4: what enzyme is used
a-ketoglutarate dehydrogenase complex
step 4: what goes over the arrows
CoA-SH and NAD+ go in, NADH and CO2 come out
step 4: what happens to the electron carriers
NAD+ converts to the reduced NADH
step 4: what is the purpose of adding CoA to the product
the product becomes activated
step 4: describe the delta G’o
large and negative
step 4: what are the implications of the large negative delta G’o
the release of the energy upon succinyl-CoA hydrolysis is used to synthesize ATP or GTP in step 5
step 5: reagent and product?
succinyl-CoA to succinate
step 5: enzyme used?
succinyl-CoA synthetase
step 5: what type of reaction is this
oxidative decarboxylation/substrate level phosphorylation
step 5: what goes over the arrow
GDP into GTP and CoA-SH
step 5: T or F: the GTP produced can also be considered to be ATP
true
step 6: reagent and product?
succinate to fumarate
step 6: enzyme used
succinate dehydrogenase
step 6: what type of reaction is this
oxidation/dehydrogenation
step 6: what happens to electron carriers
FAD reduced to FADH2
step 6: describe the location and structure of succinate dehydrogenase
membrane bound (IMM), and active site faces the matrix (plays a role in the ETC)
step 7: reagent and product?
fumarate to L-malate
step 7: enzyme used?
fumarase
step 7: type of reaction?
hydration (addition of water)
step 8: reagent and product?
L-malate to OAA
step 8: enzyme used?
L-malate dehydrogenase
step 8: what happens to electron carriers
NAD+ to reduced NADH
step 8: what type of reaction?
dehydrogenation/oxidation
how many carbons left as CO2
2
how many NADH were made
3
how many FADH2 were made
1
how many ATP/GTP were made
1
what is the name for the type of reactions that replenish either OAA or malate
anaplerotic reactions
describe how the flow of C into the CAC is controlled at the transport of pyruvate into the mitochondria
pyruvate can easily pass through large pores in the OMM, and then the mitochondrial pyruvate carrier on the IMM allows it to pass into the matrix
describe how the flow of C into the CAC is controlled at the conversion of pyruvate to acetyl-CoA
PDG complex is inhibited by reversible phosphorylation on an E1 serine. PDH includes a kinase and a phosphoprotein phosphatase to complete the regulation, and the kinase is activated by ATP
what inhibits the PDH complex
ATP, acetyl CoA, and NADH (downstream products catalyzed by PDH)
what activates the PDH complex
AMP, COA, and NAD+
which steps is the CAC regulated at
1, 3, 4 (all highly exergonic)
what inhibits the CAC
high levels of the products (ATP and NADH) and also citrate (product of step 1)
