CAC Flashcards
what enz initiates the CAC, what does it do?
pyruvate dehydrogenase oxidates pyruvate to start the formation of acetyl Co-A
this step is irriveserbale and links gly to CAC
what is th commited step of the CAC
the first step using pyruvate dehydrogenase. this commits the CAC to the synth of fatty acids
how are high transfer potential E- captured in CAC
the release of CO2 where additional e- are stored using NADH
how many enzymes are used to form ACOA
3
pyruvate dehydrigenase
dihydro-lipoyl transacetylase and
dihydro-lipoyl dehydrogenase
how many coenzymes are used to form ACOA
5
TTP
Lipoic acid
FAD
CoA
NAH+
what are the three steps in the oxidation of pyruvate into ACOA
decarboxylation
oxidation
transfer to CoA
what is the decarboxylation of the committed step
py combines with TTP anion to make hrydoxyelthyl-TTP
this is the rate limiting step for ACOA synth
oxidation of the committed step. which enzyme is responsible for this step
the TTP group on hydroxyethyl-TTP is removed (hydroxyethyl is oxidized) using lipoamide to form Acetyl-lipoamide
this is also cata by the py dehydrogenase a high E thioester bond is formed
with is the final step in the ACOA formation? which enzyme is responsible for this
Dihydrolipoyl Transaetylase moves the acetyl group on the acteyl-lipoamide to CoA. this transfer preserves the thioester bond (high E).
what is the purpose of the dihydrolipoyl dehydrogenase
to regenerate the lipoamide by oxidizing the dihydrolipoamide. during this step 2e- are transfers to FAD to make FADH2, which are then moved to NAH+ to make 1 mole of NADH +H. this step is important as another ACOA a=cannot be formed of the lipoamide arm is occupied by residual materials.
how are the three enzymes in ACOA synth connected
all are subunits of a larger enzyme labeled as the private dehydrogenase complex
the movement of the Hydroxyehtyl-TTP moves through a hydrophobic channel and transfer of the acetyl groups between the subsequent enzymes is facilitated by the lipoamide arm
at can ACOA be used for
it cannot be converted back to glucose
1) it can be fully oxidized to CO2 and used for energy
2) incorporated into fatty acids
how is the production of ACOA regulated
ACOA and NADH (products of the synthesis) are negative allosteric effectors. with in high conc, ACOA binds to E2 and NAHD binds to E3 to signal that the E needs of the cel have been met and the prod of ACOA is terminated.
E1 is regulated via covalent modification. Phosphorylation of E1 by pyruvate dehydrogenase kinase will deactivate the system. dephosphorylation of the complex by pyruvate dehydrogenase phophatase
what factors stimulate pyruvate dehydrogenase kinase
high conc of ATP and ACOA and NADH.
these promote the activity of this enzyme to phosphorylate the private dehydrogenase complex to slow ACOA synth
what factors stimulate pyruvate dehydrogenase phospatase
high conc of pyruvate and ADP
this relays the message that the cell is in need of more ACOA and ultimately energy, so the exyme will dephosphorylate the pyruvate dehydrogenase complex
what are the main products of the CAC
NADH and FADH2, these moles go further in the ETC to generate lots of ATP
how is citrate formed?
this is the first step of the CAC. here acetyl CoA mixes with oxaloacetate to make the 6C citrate unit.
this is cata by citrate synthase. Oxaloacetate binds first,, inducing a conformational change to allow Acetyl CoA to bind
which enzyme cata the formation of Isocitrate
Aconitase. This enzyme induces a dehydration followed by a hydration of citrate to form the isomer.
which enzyme cata the formation a-ketoglutarate
isocitrate dehydrogenase.This enz induces the first redox rxn.
citrate loses a CO2 unit (6C->5C) and NADH is generate
which enzyme cata the formation of succinyl CoA
a-ketoglutarate dehydrogenase complex.
this complex has three enzymes which removes a CO2 and form a thioester, oxidate (remove 2e-, captured by 2NADH) and adds and COa group to the of keto to form succinyl CoA
this is an E rich compound
which enzyme cata the formation of succinate
succinyl Coa synthetase/ succinate thiokinase
this mole will cleave the high E thioester bond and use the released energy to bind a phosphate group to ADP to make ATP (via a histidine coenzyme arm) and succinate
which enzyme cata the formation of fumarate
succinate dehydrogenase oxidizes succinate. the removed hydrogens are attached to FAD to make FADH2 bc the free energy change is not enough to reduce NAD+.
This is an important enzyme as it powers the e- transfer between CAC and ECT ti CoQ
which enzyme cata the formation of malate
fumarase hydrates fumarate to form malate
which enzyme cata the re-formation of oxaloactate
malate dehydrogenase oxidized malate and NAD+ accept the hydrogens to form NADH (1)
naturally, this rxn is non spont, but is driven forward due to the need for oxaloacetate to complete another cycle
what is the anaplerotic reaction
the conversion from pyruvate to oxaloacetate powered by pyruvate carboxylase. the reaction in particular will direct the formed oxaloacetate to the CAC instead of going to phosphoenol private kinase to further progress in the gluco cycle. this replenishes the CAC pathway when oxaloacetate stores are low.
which enzymes regulate the CAC
the allosteric enzymes isocitrate dehydrogenase and a-ketoglutarate dehydrogenase
both are inhibited by high ATP and NADH while isocitrate is stimulated by high ADP
