Glycogen, TCA Cycle and Mitochondria (Lecture 9)

Question 1

what does pyruvate dehydrogenase do and where is it found?

Answer 1

found in the mitochondria

this enzyme catalyzes the reaction of pyruvate + CoA + NAD+ –> acetyl-CoA + CO2 + NADH

Question 2

how does pyruvate get into the mitochondria?

Answer 2

since glycolysis occurs in the cytoplasm, pyruvate will enter ht mitochondria via a pyruvate translocate (H+ symport)

Question 3

what is the carbon entry point in CAC?

Answer 3

acetyl CoA

Question 4

what’s the purpose of CAC?

Answer 4

make reducing equivalents to donate electrons to the ETC

Question 5

pyruvate dehydrogenase complex is

Answer 5

a massive multi-enzyme complex

contains E1, E2, E3, E3 -binding protein, pyruvate dehydrogenase kinase, pyruvate dehydrogenase phosphatase

5 coenzymes are required:
TPP, lipoid acids, CoA, FAD, NAD+

Question 6

why re the active sites of pyruvate dehydrogenase complex in close proximity to one another?

Answer 6

so that the product of E1 is passed onto the second and so on

Question 7

E1 reaction

Answer 7

nucleophilic attack but thiamine pyrophosphatate (TPP) leadidn to a decarboxylation

C1 of pyruvate released as CO2

C2 and C3 attached to TPP as a hydroxyethyl group

this commits the PDC to generate acetyl coa, since its irreversible. it is irreversible because CO2 diffuses out of the mitochondria

in other words E1 is bound to TPP, which is required for catalysis. E1 will decarboxylate the pyruvate molecule and generate hydroxyethyl TPP

Question 8

E2

Answer 8

catalyzes the reversible steps 2 and 3

I step the hydroxyehtyl group of hydroxyethyl-TPP is oxidized to acetic acid to form acetyl-dihydrolipoamide

these 2 electrons removed in the oxidation will reduce the S-S of the lipoyl group to SH. this thirster bond is a high energy intermediate

step 2 regerates TPP to decarboxylate another pyruvate

step 3: the trans-esterification to CoA to form acetyl coa

Question 9

lipoamide is E2’s swinging arm because it is used to

Answer 9

perform substrate channeling between E1-E3

Question 10

coenzyme A fucntion

Answer 10

carrier of acetyl and other acyl groups

Question 11

E3

Answer 11

catalyses the reversible reactions of steps 4 and 5

the aim is the reset E2 and E3 in their active states and regernaets FAD and produces NADH

4. oxidation-reduction reaction that generates the oxidized E2 lipoamide (done via FAD)
5. enzyme bound FADH2 reoxidizes to FAD via NAD+ thus generating NADH 9transfer of e-)

Question 12

PDC generates and where do these substrates go?

Answer 12

acetyl coa for CAC

NADH oxidative phosphoryaltion

CO2 diffused out of mitochondria

Question 13

advantages of multi enzyme complexes

Answer 13

minimize distance for subtracters in between the active sites. this increases the reaction rate without having to maintain large pools or intermediates

metabolic intermediates are channeled between successive enzyme sites

• side reactions are minimized
• protection for them,ically labile intermediates

coordinate the control of reaction by shutting one enzyme off, it’ll shut the system off

Question 14

conversion of pyruvate to acetyl coa will

Answer 14

commit glucose carbons to oxidation in CAC or FA synthesis as for animals cant synthesize glucose from acetyl coa

Question 15

regulation of the PDC

Answer 15

2 levels:
product inhibition via NADH and acetyl coa (produced in steps 5 and 3)

covalent modification via phosphorylation of E1 (pyruvate dehydrogenase)
the phosphorylation of E1 makes it inactive

Question 16

what occurs during product inhibition

Answer 16

when acetyl coa or NADH levels are high the reactions 3 and 5 run backwards

3. acetyl coa + dihydrolipoamide –> coa + acetyl dihydrolipoamide
4. FAD-SS + NADH –>NAD+ + FADH2

this prevents useless consumption of pyruvate

when pyruvate builds up in the liver, then gluconeogensis can occur, thus increasing eh lactate in muscle to go through the cori cycle

Question 17

regulation of PDC via phosphorylation

Answer 17

inactivation via PDK

1. PDK allosterically activated but acetyl coa and NADH
2. PDK phosphorylated E1
3. E1 is inactive and shuts down he PDC

PDK is allosterically inhibited by ADP, Ca2+

reactivation via PDP

1. PDP allosterically activated by Ca2+
2. PDP dephosphoryaltes E1
3. E1 active

Question 18

utilization of pyruvate is controlled by

Answer 18

PDC and LDH

Question 19

what occurs in cancer cells with PDC activity

Answer 19

PDC activity is suppressed by PDK phosphorylation.

pyruvate is instead converted into lactate via the Warburg effect

cancer cells have hyper active PDK, which inactivates the conversion of pyruvate to acetyl coa , thus resulting in an accumulation of lactate

Question 20

regulation of PDC when stop running

Answer 20

muscle at rest
no need for ATP

acetyl coa and NADH accumulate, E2 E3 are off via product inhibition

E1 is off via phosphorylation

Question 21

regulation of PDC when start running

Answer 21

need to produce ATP

activate glycolysis to produce pyruvate

blocks PDK active E1

Ca2+ increases for mscuel contraction, thus activates PDP to keep E1 on