MC Biochem 2 > Pyruvate Oxidation > Flashcards

Pyruvate Oxidation Flashcards

(26 cards)

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1
Q

Pyruvate Oxidation

A

Links Glycolysis to TCA cycle

  • remember pyruvate has 3 fates:
  • under Aerobic conditions
  • occurs in the matrix of the mitochondria
  • irreversible reaction
  • catalyzed by the enzyme pyruvate Dehydrogenase and produces CO2 and captures High Transfer Potential electrons in the form of NADH
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2
Q

Pyruvate Dehydrogenase

A

Multienzyme complex
Composed of 3 Prosthetic Groups/2Coenzymes

Overall process preserves free energy of decarboxylation
-Free energy used to reduce NAD+ to NADH and to attach acetyl group to CoA forming Acetyl-CoA

  • E1=pyruvate dehydrogenase
  • E2= dihydrolipoyl transacetylase
  • E3= dihydrolipoyl dehydrogenase
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3
Q

Thiamine Pyrophosphate

A 
TPP
-Prosthetic Grup (E2)
Function-Aldehyde group carrier
-Thiamine (B1) vitamin precursor
-Deficiency-Beriberi
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4
Q

Lipioc Acid

A

(Lipoamide)

  • Prosthetic group (E2)-attaches to R group of Lysine
  • Function-acyl group carrier
  • Lipoid acid is vitamin precursor
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5
Q

Pyruvate Dehydrogenase (E1)

  • Reaction Type
  • Helper Molecules
  • Regulation
A

Reaction Type:
-Decarboxylation
-oxidation/reduction
OR Oxidative decarboxylation of pyruvate

Helper Molecules
-Prosthetic Groups-Thiamine Pyrophosphate (TPP)

TPP Carbanion + Pyruvate-> Hydroxyethyl-TPP + CO2

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6
Q

Dihydrolipoyl Transcetylase (E2)

  • Reaction Type
  • Helper Molecules
  • Regulation
A

Reaction Type:
-Transfer of acetyl group to CoA

Helper Molecules:

  • Prosthetic group- Lipoic acid (lipoamide)
  • Coenzyme-CoA

REGULATION:
Inhibited BY Acetyl CoA

CoA + Acetyellipoamide-> Acetyl-CoA + Dihydrolipoamide

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7
Q

Dihydrolipoyl dehydrogenase (E3)

  • Reaction Type
  • Helper Molecules
  • Regulation
A

Reaction type:

  • oxidation of dihydrolipoamide/reduction of FADH2
  • regeneration of oxidized form of Lipoamide

Helper Molecules:

  • Prosthetic group-FAD
  • Coenzyme-NAD+

Regulation:
Inhibited by NADH

Dihydrolipoamide+ FAD-> Lipoamide + FADH2-> (ADD NAD+) FAD + NADH + H+

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8
Q

Regulation of Pyruvate Dehydrogenase

A

Activated/stimulated by Dephosphorylation
Inactived/Inhibited by Phosphorylation

Allosteric regulators:
Stimulators:
-ADP
-Pyruvate

Inhibitors:

  • ATP
  • acetyl-CoA
  • NADH
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9
Q

Synonyms for Citric Acid Cycle

A

Citric Acid Cycle
TCA Cycle (Tricarboxylic cycle)
Acetyl CoA-> CO2
Krebs Cycle

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10
Q

Where does the citric acid cycle occur?

A

Matrix of Mitochondria

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11
Q

Citrate Synthase Rxn

A

Citric Acid Cycle
Acetyl-CoA(2C) + Oxaloacetate(4C) -> Citrate (6C) + CoA

Rxn Type:
Aldol Condensation followed by Hydrolysis after intermediate
Intermediate: Citryl CoA
Helper Molecules: No

Regulated YES
Allosteric:
Stimulated:
-Ca2+
-ADP
Inhibited:
-ATP
-NADH
-Succinyl CoA
-Fatty Acyl CoA
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12
Q

Citrate Synthase Enzyme

A

Dimer

Sequential Order kinetics:

1) OAA binds (2 binding sites)
2) Acetyl CoA Binds

Minimizes Side Reactions by:

  • ordered binding
  • catalytic residues crucial for hydrolysis of the thioester linkage are not in correct position until Intermediate is formed (Citryl CoA)
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13
Q

Aconitase Rxn

A

Citric Acid Cycle

Citrate-> cis-Aconitate-> Isocitrate
Reaction Type: Dehydration followed by hydration
-Isomerization
Int: cis-Aconitate
Helper Molecules NO

Regulated NO

BUT is inhibited by fluoroacetate

  • rat poision
  • fluoroacetate is converted for Fluoroacetyl-CoA, which condenses with oxaloacetate to form fluoroisocitrate which is an inhibitor of aconitase and citrate accumulates
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14
Q

Aconitase Enzyme

A

Iron Sulfur protein OR Nonheme Iron Protein

Composed of 4 Fe (iron) complexed to:

  • 3 cysteine sulfurs
  • 4 inorganic sulfides

1 Fe binds to Citrate by Carboxyl (COO-) and Hydroxyl (OH-)

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15
Q

Isocitrate Dehydrogenase Rxn

A

Citric Acid Cycle
Isocitrate-> Oxalosuccinate–> Alpha Ketogluterate + CO2

Reaction Type:
Oxidative decarboxylation
-NADH produced
-CO2 produced (after intermediate)
Helper Molecules:NONE
Regulated YES
Allosteric:
Stimulated:
ADP
Ca2+

Inhibited:
ATP
NADH

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16
Q

Alpha Ketogluterate dehydrogenase Rxn

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A

Citric Acid Cycle
Alpha Ketogluterate-> Succinyl CoA

Reaction Type:
Oxidative Decarboxylation
-Produce NADH
-Produce CO2
Helper Molecules: NONE
Regulated YES:
Allosteric:
Stimulated:
-ADP
-Ca2+

Inhibited:

  • ATP
  • NADH

SIMILAR TO PYRUVATE DEHYDROGENASSE

  • 3 subunit enzyme complex
  • 3 prosthetic groups/2 coenzymes
17
Q

Succinyl CoA Synthetase Rxn

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A

Citric Acid Cycle
Succinyl CoA-> Succinate
(AKA Succinate Thiokinase)

Reaction Type:

  • Substrate Level Phosphorylation GDP-GTP
  • use of GDP or ATP is species dependenant-USE nucleotide disphosphokinase to interconvert

Thioster=High Energy Bond

18
Q

Succinyl CoA Synthetase Enzyme

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A

A2B2 heterodimer

  • a subunit contains rossman fold
  • B subunit-contains ATP binding “Grasping” domain
19
Q

Succinate Dehydrogenase Rxn

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A

Citric Acid Cycle
Succinate-> Fumurate

Reaction Type:
Oxidation of Succinate to Fumurate
Reduction of FAD to FADH2
-links to ETC by transfer 2 e- to CoQ

Regulated:
-inhibited by oxaloacetate

20
Q

Succinate Dehydrogenase Enzyme

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A

Membrane bound Heterodimer with 3 Fe-S complexes:

  • 2Fe-2S
  • 3Fe-4S
  • 4Fe-4S
21
Q

Fumurase Rxn

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A

Citric Acid Cycle
Fumarate-> L-Malate

Reaction Type:
Hydration-reversible

22
Q

Malate is also produced in?

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A

Urea Cycle
Purine Synthesis
Catabolism of Phe and Tyr
Gluconeogenesis from converted OAA to PEP

23
Q

Malate Dehydrogenase Rxn

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A

Citric Acid Cycle
L-malate-> Oxaloacetate

Reaction Type:
Malate oxidized to Oxaloacetate
NAD+ reduced to NADH

24
Q

Replinishing Oxaloacetate

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A

Pyruvate Carboxylase

1) Part of gluconeogenesis in mammals
- High energy charge OAA converted to glucose
- low energy charge OAA replenishes citric acid cycle

25
Anapldrotic Reaction
"Fill UP" | -a reaction that leads to the net synthesis or replenishment of pathway components
26
Regulation in Citric Acid Cycle: | -Wholistic perspective
Regulation in 1st, 3rd, and 4th steps 1,2,3: stimulated: ADP Ca2+ Inhibited: ATP NADH STEP wone also inhibited by Succinyl CoA and Fatty acyl CoA
MC Biochem 2
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