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BioChem Exam 4 > Lecture 27: Glucose Catabolism (Citric Acid Cycle) > Flashcards

Lecture 27: Glucose Catabolism (Citric Acid Cycle) Flashcards

1
Q

Citric Acid Cycle (CAC) Overview

What are other names for CAC?

A

Tricarboxylic Acid Cylce (TCA) or Krebs Cycle

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2
Q

Citric Acid Cycle (CAC) Overview

How many units of CO2 are produced?

A

2

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3
Q

Citric Acid Cycle (CAC) Overview

What product of pyruvate begins the CAC?

A

Acetyl CoA

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4
Q

Citric Acid Cycle (CAC) Overview

What does Acetyl CoA react with to initiate the CAC?

A

oxaloacetate

start and finish of CAC

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5
Q

Citric Acid Cycle (CAC) Overview

What is produced through the CAC?

A

1 GTP (energy equvilent to ATP)
3 NADH
1 FADH2

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6
Q

Citric Acid Cycle (CAC) Overview

What is the general equation for the CAC?

A

Acetyl-CoA + 3 NAD + FAD + GDP + Pi + 2 H2O
–>
2 CO2 + 3 NADH + FADH2 + GTP + CoA + 3 H

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7
Q

Citric Acid Cycle (CAC) Overview

Why is it called the Citric Acid cycle?

A

The first product, the 6-carbon unit, is citic acid

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8
Q

Citric Acid Cycle (CAC) Overview

How much ATP can NADH and FADH2 produce through oxidative phosphorilation?

A

1 NADH = 2.5 ATP
1 FADH2 = 1.5 ATP

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9
Q

CAC in Eukaryotes

Where does the CAC occur?

A

mitochondrial matrix
(vs in cytosol for bacteria)

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10
Q

CAC in Eukaryotes

Where does oxidative phosphorylatoin occur?

A

mitrochondria innter membrane

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11
Q

CAC in Eukaryotes

What are the intermediates from CAC used for?

A

biosynthesis of: AA, nucleotides, fatty acids, sterols, etc

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12
Q

The Bridging Step: Oxidative Decarboxylation of Pyruvate

What enam catalyzed the transition from pyruvate to Acetyl CoA?

A

Pyruvate dehydrogenase

regulated by phosphorylation

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13
Q

The Bridging Step: Oxidative Decarboxylation of Pyruvate

What are the 5 cofactors required for pyruvate dehdrogenase?

A

TPP, lipoic acid, and FAD (prosthetic groups)
NAD and CoA-SH (co-substrates)

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14
Q

The Bridging Step: Oxidative Decarboxylation of Pyruvate

Q from Slides: The conversion of 1 mole of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the CAC also yield ____ mol of NADH, ____ mol of FADH2, and ____ mol of ATP (GTP)?

A

4 mol NADH
1 mol FADH2
1 mol ATP (GTP)

Pyruvate to Acetyl CoA produce an extra NADH

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15
Q

CAC

How many steps/enzymes are there for the CAC?

A

8

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16
Q

CAC

Step 1:

A

C-C bond formation to make Citrate:
condensation between a 2-carbon units (oxaloacetate, OAA) and 4 carbon units (acetyl-CoA) to make 6 carbon units (Citric Acid)
catalyzed by citrate synthase

The first 2 CO2 produced originate from the OAA not acetyl-CoA

17
Q

CAC

Step 2:

A

Isomerization via dehydration/rehydration:
Aconitase isomerized citrate to isocitrate as isocitrate is easily oxidized. Converts the 3° alcohol to 2° alcohol (switches the OH group)
dehydrogenation first to cis-Aconitate then rehydration to form isocitrate

18
Q

CAC

Step 3:

A

Oxidative decarboxylations to give NADH:
Isocitrate dehydrogenase oxidiazed the isocitrate to oxalosuccinate (a-keto acid), which forms NADH. Oxalosuccinate is than decarboxylated to for a-ketoglutarate

19
Q

CAC

Step 4:

A

Oxidative decarboxylations to give NADH and CO2:
a-ketoglutarate dehydrogenase oxidatively decarboxylates a-ketoglutarate into succinyl-CoA
irreversible, regulated by product inhibition

final oxidative decarboxylation

20
Q

CAC

Step 5:

A

Substrate-level phosphorylation to give GTP:
Succinyl-CoA synthetase converts succinyl-CoA to succinate
gives phosphate group to GDP to form GTP (GTP to ATP is realatively simple and just involves transfering the phosphate to ADP using the enzyme nucleoside diphosphokinase)

21
Q

CAC

Step 6:

A

Dehydrogenation to give reduced FADH2:
oxidation of succinate is catalyzed by succinate dehydrogenase to form fumarate
Formation from a single C-C bond to a trans double C-C bond.
also forms FADH2

enam is part of complex II in ETC

22
Q

CAC

Step 7:

A

Hydration:
catalyzed by Fumarase. Hydrates the double bond to produce a single bond Malate

23
Q

CAC

Step 8:

A

Dehydrogenation to give NADH:
Malate dehydrogenase reforms the oxaloacetate by oxidizing the secondary OH of Malate to a ketone
final step of cycle
forms 3rd and final NADH

24
Q

Regulation of CAC

What is the CAC activated by?

A

Substrate Availability

NAD and AMP

25
Q

Regulation of CAC

What is the CAC inhibited by?

A

product accumulation

NADH and ATP

26
Q

Regulation of CAC

Which enzymes regulate rate-limited steps?

A

Citrate Synthase: ATP, NADH, and succinyl-CoA inhibit

Isocitrate dehydrogenase: ATP inhibits, ADP and NAD activate

a-Ketoglutarate dehydrogenase: NADH and succinyl-CoS inhibit, AMP activates

27
Q

Plants/bacteria

What cycle do plants and some bacteria have similar to CAC?

A

Glyoxylate Cycle

28
Q

Plants/Bacteria

What are the differences in Glycoxylate cycle and CAC?

A

Glycoxylate skips the decarboxylation of CAC to form glycoxylate

Also has 2 new enams, isocitrate lyase and malate synthase

BioChem Exam 4 (8 decks)

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