Biochemistry Exam 3: Citric Acid Cycle

Front 1

What happens in citric acid cycle?

Back 1

It reduces carbon structures down to CO2 and produces reducing equivalents used in electron transport and then reoxidized by O2. It is central pathway for recovering energy from carbs, fatty acids, and amino acids. It also provides intermediates for other reactions and pathways.

Front 2

Citric Acid Cycle is a series of how many reactions.

Back 2

8

Front 3

What is the general overall process of the citric acid cycle.

Back 3

The acetyl CoA is oxidized into two molecules of CO2\

Front 4

What is yielded in one complete cycle?

Back 4

2 CO2, 1 FADH2, 3 NADH, 1 GTP or ATP

Front 5

What is considered central hub of all metabolism?

Back 5

Citric Acid Cycle

Front 6

Where does citric acid cycle occur in eukaryotes?

Back 6

In mitochondria

Front 7

T/F the carbon atoms of acetyl CoA are the same ones leaaving as CO2.

Back 7

False

Front 8

What does oxidation of acetyl CoA to 2 CO2 require?

Back 8

transfer of 4 pairs of electrons -> reduction of 3 NAD+ to 3 NADH accounts for 3 pairs and reduction of FAD to FADH2 accounts for 4th pair

Front 9

What are final products of glycolysis under aerobic conditions?

Back 9

Pyruvate and NADH

Front 10

How are pyruvate and H+ moved into mitochondria?

Back 10

Pyruvate H symport

Front 11

What is pyruvate dehydrogenase multienzyme complex?

Back 11

It is group of noncaovalently bound associated enzyme complexes

Front 12

What are the advantages of multienzyme complexes?

Back 12

minimized enhancing reaction rates, minimizes side reactions, and can coordinately control reactions

Front 13

What are the three enzymes that make up pyruvate dehydrogenase complex?

Back 13

Pyruvate dehdorgenase E1, Dihydolipoyl transacetylase E2, Dihydroplipoyl dehydrogenase E3

Front 14

What makes up the core of the dehydrogenase complex?

Back 14

60 units of E2

Front 15

What surrounds the core of this dehydrogenase complex?

Back 15

30 E1 and 12 E3

Front 16

What does the pyruvate dehydrogenase complex do?

Back 16

It catalyzes 5 sequential reactions with the overall stochiometer of pyruvate + CoA + NAD+ -> acetyl CoA + CO2 + NADH

Front 17

What are the five different cofactors required with pyruvate dehydrogenase reactions?

Back 17

TPP, Lipamide, CoA, FAD, NAD+

Front 18

What is the 1st reaction of Pyruvate Dehydrogenase complex?

Back 18

E1 is bound to TPP. This decarboxylates pyruvate and forms hydroxyethyl TPP intermediate

Front 19

What is the second reaction of Pyruvate Dehydrogenase?

Back 19

Hydroxyethyl group transferred to next enzyme E2 which contains lipamide group. The hydroxyethyl group is oxidized to acetyl group as lipamide disulfide is reduced. Because the lipoamide attacks the hydroxyethyl and removes the TPP.

Front 20

What is the third reaction of pyruvate dehydrogenase complex?

Back 20

E2 catalyzes transesterification reaction in which acetyl group transferred to CoA yielding Acetyl CoA and dihydrolipamide-E2

Front 21

What is fourth reaction of dehydrogenase complex?

Back 21

Acetyl CoA formed and E2 lipamide must be regenerated. E3 reoxidizes dihydrolipoamide resulting in disulfide interchange reaction. E3 contains disulfide group and FAD.

Front 22

What is the 5th reaction of pyruvate dehydrogenase complex?

Back 22

E3 reoxidized and sulfhydryl groups reoxidized by FAD funneling electrons to NAD+ to yield NADH

Front 23

What does arsenic do to dehydrogenase complex?

Back 23

It inhibits lipamide containing enzymes. Such as pyruvatedehdrogenase and stops respiration of Citric Acid Cycle

Front 24

What was arsenic once used for and why?

Back 24

Syphillis treatment because mor toxic to bacteria

Front 25

What is the function of Citric Synthase?

Back 25

It catalyzes condensation of acetyl CoA and oxaloacetate. This is when carbon atoms from carbs, fatty acids and amino acids enter cycle

Front 26

What is a key characteristic of this citrate synthase reaction?

Back 26

It is ordered sequential kinetic mechanism in which oxaloacetate binds prior to acetyl CoA

Front 27

Describe the structure of citrate synthase.

Back 27

It is dimer in open form with two domains forming cleft containing oxaloacetate binding site. Once oxaloacetate binds it rotates the enzyme opening up acetyl CoA binding site

Front 28

What is the proposed mechanism of citrate synthase?

Back 28

Enol of acetyl CoA generated in rate limiting step when proton removed from methyl group. His 274 forms H bond with enolate and Citryl CoA formed which is hdyrolyzed to Citrate and Coa

Front 29

wHAT DOES ACONITASE DO?

Back 29

It catalyzes reversible isomerization of citrate and isocitrate with cis-aconitate as intermediate

Front 30

How does aconitase reaction begin?

Back 30

With dehydration

Front 31

Describe the citrate group and what happens with the removal of one carboxymethyl group attached to central C atom.

Back 31

It is prochiral and rmeoval or modicication of one group makes C atom chiral.

Front 32

Where does aconitase remove water from citrate?

Back 32

Lower arm

Front 33

What does aconitase contain?

Back 33

Iron Sulfur cluter and this coordinates OH group of citrate to facilitate elimination

Front 34

What is second stage of aconitase reaction?

Back 34

It is rehydration of double bond of cis-aconitate to isocitrate

Front 35

What does isocitrate dehydrogenase do?

Back 35

It catalyzes oxidative carboxylation of isocitrate to alpha ketoglutarate

Front 36

Why is Mn or Mg required as cofactor for isocitrate dehydrogenase?

Back 36

It helps polarize newly formed carbonyl group

Front 37

What is the function of alpha ketoglutarate dehydrogenase?

Back 37

It catalyzes oxidative decarboxylation of alpha ketoglutarate and produces 2nd CO2 and NADH of TCA cycle. It produces succinyl CoA

Front 38

What does siccinyl CoA synthetase do?

Back 38

It couples cleavage of high energy succinyl CoA to synthesis of high energy nucleoside triphosphate GTP

Front 39

What is the three step process of succinyl CoA synthetase?

Back 39

succinyl CoA reacts with Pi forming succinyl phosphate and CoA

Then phosphoryl group is transferred from succinyl Phosphate to His residue on E releasing succinate

Phosphoryl group on E transferred to GDP to make GTP

Front 40

What does succinate dehydrogenase do?

Back 40

It catalyzes sterospecific dehydrogenation of succinate to fumarate.

Front 41

What does dehdrogenation of succinate make?

Back 41

FADH2 and fumurate

Front 42

Why is succinate dehydrogenase unique in TCA cycle?

Back 42

It is the only membrane bound enzyme of TCA so it can funnel electreons directly into electron transport chain

Front 43

What does Fumarase do?

Back 43

It catalyzes hydration of double bond of fumarate to form malate.

Front 44

What does malate dehydrogenase do?

Back 44

It catalyzes final TCA reaction of regeneration of oxaloacetate. OH group of malate is oxidized in NAD + dependent reaction

Front 45

How is TCA cycle closely regulated?

Back 45

substrate availability, need for TCA cycle intemediates as biosynthetic precursors, demand for ATP

Front 46

How many ATP is each NADH and each FADH2 responsible for?

Back 46

3 nadh AND 2 FADH2 so TCA CYCLE PRODUCES 12ATP

Front 47

What are the regulatory systems of pyruvate dehydrogenase?

Back 47

1ST is product inhibition by NADH and acetyl CoA since they are competitive inhibitors with NAD and CoA binding sites NADH and acetyl CoA also drive E2 AND E3 backwards

2nd regulatory system is covalent modification of E1. If pyruvate dehydrogenase kidnase is activated by NADH and acetyl CoA then phosphorylization inactivates multienzyme complex

Front 48

How do pyruvate and ADP function to regulate pyruvate dehydrogenase?

Back 48

They inhibit pyruvate dehydrogenase kinase

Front 49

What about Ca?

Back 49

It inhibits ppyruvate dehydrogenase kinase and activates phyruvate dehydrogenase phosphatase