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BB10003 Biochemistry > Citric Acid Cycle and Glyoxylate Cycle > Flashcards

Citric Acid Cycle and Glyoxylate Cycle Flashcards

1
Q

Basic Metabolic Fate of pyruvate

A

Glucose –> Pyuvate –> Lactate

  • 2NAD+ –> 2NADH.H+
  • ATP produced
  • O2 can regenerate NAD
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2
Q

Basic Metabolic Fate of pyruvate IN YEAST

A

Pyruvate –> Ethanal –> Ethanol

  • NADH.H+ –> NAD+
  • Enzyme Pyruvate Decarboxylase
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3
Q

Link Reaction

A

Pyruvate + CoASH + NAD+ –> Acetyl CoA + CO2 + NADH.H+

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4
Q

Enzymes in Prokaryotes + Eukaryotes

A
  • E2 is catalytic and structural core of complex
  • E.coli has 24 copies of E2
  • E1 and E3 bound to it
  • 48 E1 : 24 E2 : 24 E3
  • Eukaryote has 60 copies in a pentagonal dodecahedron 5 x 12 = 60
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5
Q

PDHC Link Reaction ENZYMES

Stage 1 -

A

E1 - Pyruvate Decarboxylase
E2 - Lipolylacetyltransferase
Cofactor [TPP-H] Thiamin Pyro-Phosphate

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6
Q

PDHC Link Reaction ENZYMES

Stage 2 -

A

E2 -
[S-S] Lipoic Acid
\lip/

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7
Q

PDHC Link Reaction ENZYMES

Stage 3 -

A

E3 - Dihydro lipamide dehydrogenase

Complex formed which has 1) Flavin Adenine Dinucleotide 2) Histidine

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8
Q

What is E2 in Link Reaction consisting of?

A
  • Long swinging Lysine arm
  • Lipoic Acid
  • Lipoic acid communicates with E1,2,3
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9
Q

Carbons of the Citric Acid Cycle

A

C3 —> C2 + C4 —> C6 —> C4 (C2 RELEASED INBETWEEN C6 AND C4, C4 GOES BACK ROUND TO C6)

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10
Q

General equation for Citric Acid Cycle

A

Pyruvate + 3H2O –> 3CO2 + 10H

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11
Q

Enzymes in order of the CAC

A

1) Citrate Synthase
2) Aconitase
3) Isocitrate Dehydrogenase
4) 2-Oxoglutarate Dehydrogenase Complex
5) Succinate Thiokinase
6) Succinate Dehydrogenase
7) Fumerase
8) Malate Dehydrogenase

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12
Q

Enzymes in order of the Glyoxylate Cycle

A

9) Isocitrate Lyase

10) Malate Synthase

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13
Q

Step 1 - Citrate Synthase

A
  • attraction of a proton off acetyl CoA
  • asp-COO- attacks CH3 group of acetyl CoA to get proton
  • Eq lies to left (+^G) between O=C,(CH2COOH)–COOH
    and Citryl-SCoA
  • Hydrolysis of C-SCoA bond -^G
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14
Q

Mechanism of Isocitrate Dehydrogenase

A
  • enzyme determines that COOH in central C is decarboxylated
  • Isocitrate —> 2 intermediates —> 2-oxoglutarate
  • H removed
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15
Q

Enzymes forming 2-Oxoglutarate dehydrogenase complex

A

E1 - 2-oxoyglutarate decarboxylase
E2 - Lipoyl-succinyl transferase (24 of these)
E3 - Dihydrolipoamide dehydrogenase

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16
Q

^G = -RT ln Keq

A

^G = ^H - T^S

- ^S is highly positive ^G is highly negative in decarboxylation reaction

17
Q

Succinyl-SCoA has high free energy meaning

A

High -^G to make atp

18
Q

Functions of the CAC 1) Final Oxidation

A 
1) Final Oxidation -
Carbs-->Sugars-->Pyruvate
Fats-->fattyacids-->Acetyl-SCoA (C2)
Fats/Tryglycerides --> Glycerol
Proteins--->Amino acids
- Transamination
19
Q

Functions of the CAC 2) Energy

A 
NADH + H+ --ETC--> 3ATP X 4 --> 12 ATP
FADH2 ---> 2ATP X 1 ---> 2 ATP
SUCCTK ---> 1 ATP
TOTAL - 15 PER PYRUVATE 
30 PER GLUCOSE 
2PGM IN GLYCOLYSIS
20
Q

Functions of the CAC 3) Biosynthesis

A
  • Oxaloacetate —> Carbohydrates (gluconeogenesis)
  • Acetyl CoA —> Fatty Acids
  • Pyruvate —> Alanine (via reverse transalanation)
21
Q

Citric acid cycle regulation of energy

A
  • kinase carry out reactions with high energy compounds
  • PDHC ——–> PDHC-P
  • substrates include, pyruvate and CoA
  • products include, acetyl SCoA, NADH
  • Ca2+ inhibits kinase/activates phosphatase
  • insulin stimulates phosphatase
  • 4 kinases
  • 3 phophates added to E1 component
  • E1 is enzyme that’s phosphorylated
  • insulin phosphorylates phosphate
22
Q

Regulation of Citrate Synthase

A
  • ATP- inhibits citrate synthase
  • ATP is an analog of CoA (competitive active site)
  • inhibition between ATP and CoA
23
Q

Regulation of Isocitrate dehydrogenase

A
  • Ca2+, ADP, AMP all activators
  • ATP inhibitor
  • ADP mammalian AMP yeast
24
Q

Regulation of Oxoglutarate dehydrogenase complex

A
  • Ca2+ activates it
  • 3 enzymes PDHC, ISO DH, OGDHC, all activated by Ca2+
  • Ca2+ floods into cells and mitochondria
  • muscular action occurs
  • hormones e.g. adrenaline also stimulate muscular action
25
Q

Anaplerotic reactions

A
  • filling up
  • intermediates taken out of cycle for biosynthesis
  • OAA is not regenerated
  • OAA —> Citrate
26
Q

Complications affecting overall yield…

A
  • ATP being used up so there’s not 30 made
  • pyruvate carboxylase requires acetyl SCoA as if acetyl SCoA builds up theres not enough OAA to take it up so it stimulates pyruvate decarboxylase and inhibits kinase
27
Q

Coupling reactions

A
  • lysine - biotin (coupled)
    Need this because:
  • enzyme - biotin + ATP + HCO3- Co2 - biotin - enzyme + ADP + Pi
  • CO2 - biotin -enzyme +pyruvate biotin-enz + OAA
28
Q

Glyoxylate Cycle

A
  • only one thing normally happens to acetyl coa in this context, it goes to make CO2
  • can’t grow on acetate/acetyl coa if you rely on citric acid cycle as all your carbons go to CO2
  • eat fatty food —> store or use, can’t convert it to glucose using CAC
  • plants therefore bypass Citrate —> OAA where CO2 is release called GC
29
Q

What is done in Glyoxylate Cycle?

A
  • make extra C4
  • C4 + 2C2 —> C4 + C4
  • OAA + A.COA —> SUCCINATE + MALATE
  • succinate goes back to OAA which is used again
  • malate goes to make OAA which is used for biosynthesis
30
Q

Pyruvate carboxylase requires what to work?

A

requires an enzyme attached biotin moiety for catalysis

31
Q

The conversion of pyruvate to acetyl-SCoA is catalysed by…

A

the pyruvate dehydrogenase complex

32
Q

Eukaryotic PDHC is covalently regulated by:

A

phosphorylation

33
Q

eukaryotic 2-oxoglutarate dehydrogenase complex is stimulated by:

A

Ca2+

34
Q

In plants, in which organelle are the enzymes of the glyoxylate cycle situated?

A

glyoxysome

35
Q

What is the cofactor involved in the mechanism of pyruvate carboxylase?

A

biotin

BB10003 Biochemistry (5 decks)

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