CAC

Question 1

what enz initiates the CAC, what does it do?

Answer 1

pyruvate dehydrogenase oxidates pyruvate to start the formation of acetyl Co-A

this step is irriveserbale and links gly to CAC

Question 2

what is th commited step of the CAC

Answer 2

the first step using pyruvate dehydrogenase. this commits the CAC to the synth of fatty acids

Question 3

how are high transfer potential E- captured in CAC

Answer 3

the release of CO2 where additional e- are stored using NADH

Question 4

how many enzymes are used to form ACOA

Answer 4

3
pyruvate dehydrigenase
dihydro-lipoyl transacetylase and
dihydro-lipoyl dehydrogenase

Question 5

how many coenzymes are used to form ACOA

Answer 5

5

TTP
Lipoic acid
FAD
CoA
NAH+

Question 6

what are the three steps in the oxidation of pyruvate into ACOA

Answer 6

decarboxylation
oxidation
transfer to CoA

Question 7

what is the decarboxylation of the committed step

Answer 7

py combines with TTP anion to make hrydoxyelthyl-TTP

this is the rate limiting step for ACOA synth

Question 8

oxidation of the committed step. which enzyme is responsible for this step

Answer 8

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

Question 9

with is the final step in the ACOA formation? which enzyme is responsible for this

Answer 9

Dihydrolipoyl Transaetylase moves the acetyl group on the acteyl-lipoamide to CoA. this transfer preserves the thioester bond (high E).

Question 10

what is the purpose of the dihydrolipoyl dehydrogenase

Answer 10

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.

Question 11

how are the three enzymes in ACOA synth connected

Answer 11

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

Question 12

at can ACOA be used for

Answer 12

it cannot be converted back to glucose

1) it can be fully oxidized to CO2 and used for energy
2) incorporated into fatty acids

Question 13

how is the production of ACOA regulated

Answer 13

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

Question 14

what factors stimulate pyruvate dehydrogenase kinase

Answer 14

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

Question 15

what factors stimulate pyruvate dehydrogenase phospatase

Answer 15

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

Question 16

what are the main products of the CAC

Answer 16

NADH and FADH2, these moles go further in the ETC to generate lots of ATP

Question 17

how is citrate formed?

Answer 17

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

Question 18

which enzyme cata the formation of Isocitrate

Answer 18

Aconitase. This enzyme induces a dehydration followed by a hydration of citrate to form the isomer.

Question 19

which enzyme cata the formation a-ketoglutarate

Answer 19

isocitrate dehydrogenase.This enz induces the first redox rxn.

citrate loses a CO2 unit (6C->5C) and NADH is generate

Question 20

which enzyme cata the formation of succinyl CoA

Answer 20

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

Question 21

which enzyme cata the formation of succinate

Answer 21

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

Question 22

which enzyme cata the formation of fumarate

Answer 22

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

Question 23

which enzyme cata the formation of malate

Answer 23

fumarase hydrates fumarate to form malate

Question 24

which enzyme cata the re-formation of oxaloactate

Answer 24

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

Question 25

what is the anaplerotic reaction

Answer 25

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.

Question 26

which enzymes regulate the CAC

Answer 26

the allosteric enzymes isocitrate dehydrogenase and a-ketoglutarate dehydrogenase

both are inhibited by high ATP and NADH while isocitrate is stimulated by high ADP