3.5 ETC

Question 1

name the three steps of pyruvate dehydrogenase complex (the whole machine is not enzyme but total of three enzymes so it is enzyme machine)

Answer 1

1. pyruvate dehydrogenase
2. dihydrolipoamide transacetylase
3. dihydrolipoamide dehydrogenase

Question 2

what does pyruvate dehydrogenase do?

Answer 2

pyruvate dehydrogenase will go through redox and decarboxylation of pyruvate

it will decarboxylate the pyruvate
movethe acetyl group of the pyruvate onto the TPP

Question 3

lipoamide vs lipoic acid

Answer 3

lipoic acid is free of lysine res + enzyme

lipoamide is attached to the lysine but can reduced to dihydrolipoamide with two SH

Question 4

Dihydrolipoamide/dihydrolipoyl transacetylase (E2)

Answer 4

—transfers the acetyl group from TPP in E1 to bound lipoamide cofactor, and then from lipoamide to CoA resulting in the reduction of lipoamide to dihydrolipoamide

Question 5

Dihydrolipoamide/dihydrolipoyl dehydrogenase (E3)—

Answer 5

oxidizes dihydrolipoamide to lipoamide in E2 using FAD and NAD+ as oxidizing agents
Lipoic so that it can be reused again

Question 6

Thiamine pyrophosphate aka tpp

Answer 6

prosthetic group in E1 but not covalent and its carbanion will react with the pyruvate to form ethylhydroxy carbanion pyruvate

Question 7

lipoamide aka lpa

Answer 7

Hydroxyethyl carbanion is subsequently oxidized to an acetyl group with concomitant reduction of lipoamide resulting in the formation of acetyl-dihydrolipoamide-E2 intermediate and regeneration of active TPP.E1

Question 8

coenzyme A

Answer 8

co substrate in E2 that takes the acetyl group from the dihydrolipoamide and places it on acetyl coA

Question 9

flavin adenine diphosphate (FAD)

Answer 9

-prosthetic group in E3 noncovalently bounded and reduced by lipoamide
has a sugar called ribitol (five carbons)
takes both the H from S

Question 10

FAD relationship to E3

Answer 10

• In so doing, the disulfide linkage of E3 becomes reduced to thiol groups resulting in the conversion of E3(ox).FAD complex to E3(red).FAD intermediate

Question 11

Krebbs cycle is what main focus

Answer 11

involves the oxidation of acetyl group of acetyl-coenzyme A (acetyl-CoA) to CO2 with concomitant release of NADH, FADH2, and GTP

Question 12

citrate synthase

Answer 12

pyruvate and oxaloate to make iso citrate

Question 13

aconitase

Answer 13

lyase bc it breaks bond and isomerizes citrate withloss of h20 to make cis citrate and with loss of another water will become citrate

Question 14

isocitrate dehydrogenase

uses energy

Answer 14

uses energy and cofactor mn2+
Oxidation of isocitrate (using NAD+ as oxidizing agent) to oxalosuccinate intermediate harboring a newly formed carbonyl group with concomitant release of NADH
oxalosuccinate will go through decarboxylation and will lose co2 to become alpha ketoglutarate

Question 15

alpha keto dehydrogenase

use energy

Answer 15

Oxidation of -ketoglutarate (using NAD+ as oxidizing agent) facilitates the release of a CO2 molecule

(b) Transfer of the thiol group of CoA-SH generates “high-energy” succinyl-CoA

Question 16

Succinyl-CoA Synthetase

Answer 16

uses energy
picks up phosphate and exhanges it with co A to make phosphoanhydride

Catalyzes the cleavage of “high-energy” succinyl-CoA to succinate coupled with the synthesis of “high-energy” GTP via three steps: (1) Condensation of Pi and succinyl-CoA to generate succinyl-phosphate (SucP) and CoA (2) Transfer of phosphoryl group of SucP to a histidine on the enzyme so as to release succinate (3) Transfer of phosphoryl group from the histidine on the enzyme to GDP to generate GTP

Question 17

Succinate Dehydrogenase

Answer 17

fumerate is only compound with double bond and only one that uses FAD?

Catalyzes dehydrogenation of succinate to fumarate (didehydrosuccinate) using FAD (covalently bound to the enzyme via a histidine residue) as an oxidizing agent (more powerful than NAD+):

Question 18

Fumarase

Answer 18

hydration of C=C double bond in fumarate (didehydrosuccinate) to malate (alpha-hydroxysuccinate):

(a) Nucleophilic attack of an hydroxyl anion (from H2O) on C=C double bond in fumarate generates a carbanion intermediate
(b) Protonation of carbanion intermediate generates malate

Question 19

Malate Dehydrogenase

Answer 19

Catalyzes oxidation of malate (alpha-hydroxysuccinate) to oxaloacetate (alpha-ketosuccinate):

(a) Electrons in the form of an hydride ion are funneled to NAD+ so as to oxidize the hydroxyl moiety in malate to a keto group in oxaloacetate