Synthesis Of Acetyl-CoA

Question 1

What is the citric acid cycle

Answer 1

Is a pathway to obtain energy from carbohydrates, fatty acids, amino acids. These are broken down into acetyl-coA and then oxidized

Question 2

The enzymes of the TCA are where

Answer 2

In the matrix of the mitochondria

Question 3

What is pyruvate dehydrogenase and what are it’s subunits

Answer 3

It is a multienzyme complex made of : E1 (pyruvate dehydrogenase), E2 (dihydrolipoyl transacetylase), E3 (dihydrolipoyl dehydrogenase), E4 (E3BP)

Question 4

What makes up the central core and outer shell of pyruvate dehydrogenase

Answer 4

Central core is made of 60 E2 subunits (which have a dodecahedral symmetry) combine with 12 E3BP. The outer shell is made of 9 E3 subunits (are homodimers) partly embedded in the E2 core and 45E1 heterotetramers from a shell around the E2/E3BP core

Question 5

What are cofactprs of the pyruvate dehydrogenase enzyme

Answer 5

3 prosthetic groups : TPP, Lipoamide, FAD

2 cosubstrates : coA, NAD+

Question 6

Where is TPP, function?

Answer 6

Bound to E1, decarboxylates pyruvate, yields a hydroxyethyl TPP carbanion

Question 7

Where is Lipoamide and what’s it’s function

Answer 7

Linked to Lys on E2, it accepts the hydroxyethyl carbanion group as an acetyl group

Question 8

Where is coA and what is it’s function

Answer 8

It’s a substrate for E2, accepts the acetyl group from lipoamide

Question 9

Where is FAD and what is it’s function

Answer 9

Is bound to E3, it is reduced by lipoamide

Question 10

Where is NAD+ and what is it’s function

Answer 10

It is reduced by FADH2

Question 11

The active form of thiamine is TPP, what are it’s functions

Answer 11

Needed for pyruvate decarboxylase in alcohol fermentation, for transketolase in PPP, in decarboxylation of pyruvate , synthesis of Ach and GABA and leu and Val

Question 12

The constituents of acetyl coA are

Answer 12

3’-phosphoadenosine diphosphate, pantothenic acid, beta- mercapto ethylamine, acetyl group

Question 13

Riboflavin is made of

Answer 13

D-ribitol and isoalloxazine

Question 14

FMN is made of

Answer 14

Isoallaxozanine, D-ribitol, phosphate group

Question 15

FAD is made of

Answer 15

D-ribitol, isoallaxozanine, phosphate group, AMP

Question 16

List the specifics between hydride ion transfer when going from the oxidized form to the reduced form of nicotinamide

Answer 16

The N+ attracts electrons so it makes the transfer of H+ easier, the H+ addition site is prochiral, the transfer is steroespecific

Question 17

What are the components and individual functions of the subunits of the pyruvate dehydrogenase complex and how they help the formation of acetyl coA

Answer 17

E1- contains TPP and catalyses reaction 1+2 , E2- contains lipoamide and catalyses reaction 3, E3- contains FAD with a SS in a redox center and catalyses reaction 4 and 5

Question 18

What is reaction 1

Answer 18

The pyruvate dehydrogenase (E1) decarboxylates pyruvate and forms hydroxyethyl TPP

Question 19

What is reaction 2

Answer 19

The Lipoamide accepts the hydroxyethyl group and the hydroxyethyl carbanion is oxidized into acetyl and the Lipoamide disulfide bonds are reduced

Question 20

What is reaction 3

Answer 20

The dihydrolipoyl transacetylase catalyses the transfer of the acetyl from the Lipoamide onto coA. This is a transesterification reaction

Question 21

What is reaction 4

Answer 21

Dihydrolipoyl dehydrogenase oxidizes dihydrolipoamide by reducing the S-S bond into 2 S-H bonds in the FAD redox center, this is a disulfide exchange

Question 22

What is reaction 5

Answer 22

It is catalysed by E3, the 2 S-H bonds in the FAD redox center are reoxidized into S-S bonds, FAD gives electrons to NAD+ forming NADH

Question 23

What is the lipoyllysyl arm

Answer 23

It is a structure of the E2 subunits of the pyruvate dehydrogenase complex, it is used to transfer intermediates

Question 24

ATP synthesis happens in the

Answer 24

inner mitochondrial membrane

Question 25

PDH is allosterically inhibited by

Answer 25

acetyl coA, NADH, ATP

Question 26

PDH is allosterically enhanced by

Answer 26

AMP

Question 27

PDH is covalently inhibited by

Answer 27

pyruvate DH kinase, WHICH IS stopped by Ca2+, pyruvate, ADP and encouraged by NADH and acetyl coA

Question 28

PDH is covalently encouraged by

Answer 28

pyruvate DH phosphatase, which is encouraged by insulin, Ca2+, Mg2+