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BCM210 > Topic 13 - Citric Acid Cycle > Flashcards

Topic 13 - Citric Acid Cycle Flashcards

1
Q

*Define cellular respiration & ID 3 stages of aerobic respiration

Define respiration

A

Process in which chemical bonds of energy rich molecules (glucose, proteins, FA) are converted into energy useable forms for life processes (ATP).

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2
Q

_​*Define cellular respiration & ID 3 stages of aerobic respiration_

Define Anaerobic respiration

A

Involves glycolysis & fermentation to lactate or ethanol. 2 ATP produced in glycolysis

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3
Q

_​*Define cellular respiration & ID 3 stages of aerobic respiration_

Define aerobic respiration and ID the 3 stages

A
  • Complete oxidation of glucose (pyruvate) to Co2 ***& H2O
  • 30-32 ATP produced***
  • Requires O2 =>terminal electron acceptor
  • Occurs in mitchondria
  • 3 stages:
  • 1. Formation of acetyl-CoA
    2. Citric Acid cycle
    3. Oxidative phosphorylation    *
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4
Q

​*Define cellular respiration & ID 3 stages of aerobic respiration

*Describe the “link” reaction incl. components of the pyruvate DH complex & cofactors

Define stage 1 of aerobic respiration and the link reaction

A
  • Acetyl-CoA formed from glucose, FA or aa
  • Link reaction: conversion of pyruvate to acetyl-CoA
  • Irreversible rxn
  • Occurs in mitochondrial matrix
  • Catalysed by pyruvate DH complex
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5
Q

​*Define cellular respiration & ID 3 stages of aerobic respiration

*Describe the “link” reaction incl. components of the pyruvate DH complex & cofactors

Describe pyruvate DH complex, its enzymes & cofactors

A
  • Composed of 3 distinct enzymes to form a ***multiple enzyme complex:
  • *****E1 (thiamine pyrophosphate attached)
  • E2 (lipolic acid att.)
  • E3 (FAD att.)**
  • 5 cofactors:
  • **-Coenzyme A
  • NAD+***
  • **-FAD
  • Thiamine pyrophosphate (TPP)
  • Lipolic acid***
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6
Q

​*Define cellular respiration & ID 3 stages of aerobic respiration

Describe the 3 distinct chemical transformations undergone in stage 1 of aerobic respiration

A
  • 1. Decarboxylation rxn- 3C=>2C compound, w/ release of CO2
  • 2. Acylation rxn- carboxylic acid group attached to thiol of HSCoA, forming acetyl-CoA
  • 3. REDOX rxn- formation of NADH
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7
Q

_​*Define cellular respiration & ID 3 stages of aerobic respiration_

_*Explain each of the steps in the Citric Acid Pathway (actual pathway given in exam)_

STAGE 2

Describe RXN 1

A
  • High energy
  • Catalysed by citrate synthase (synthase=absence of ATP requirement)
  • Irreversible, condensation rxn
  • 1st C of acetyl-CoA (2C) is joined to carbonyl group of oxaloacetate (4C)
  • Coenzyme A liberated
  • Energy released from hydrolysis of thioester bond of acetyl-CoA drives rxn.
  • ∆G’ ˚ = -32.2kJ/mol
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8
Q

_​*Define cellular respiration & ID 3 stages of aerobic respiration_

_*Explain each of the steps in the Citric Acid Pathway (actual pathway given in exam)_

STAGE 2

Describe RXN 2

A
  • Catalysed by Aconitase
  • Reversible, dehydration (a) => hydration (b) rxn
  • Citrate is isomerised to isocitrate
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9
Q

​*Define cellular respiration & ID 3 stages of aerobic respiration

*Explain each of the steps in the Citric Acid Pathway (actual pathway given in exam)

STAGE 2

Describe RXN 3

A
  • High energy
  • Catalysed by Isocitrate DH
  • Irreversible, oxidative decarboxylation rxn
  • Isocitrate (6C) is oxidised then decarboxylated to a-ketoglutarate (5C)
  • CO2 released, NAD+ electron acceptor
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10
Q

​*Define cellular respiration & ID 3 stages of aerobic respiration

*Explain each of the steps in the Citric Acid Pathway (actual pathway given in exam)

STAGE 2

Describe RXN 4

A
  • High energy
  • Irreversible, oxidative decarboxylation rxn
  • a-ketoglutarate (5C) is decarboxylated & oxidised to succinyl-CoA (4C)
  • CO2 released, NAD+ reduced to NADH
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11
Q

_​*Define cellular respiration & ID 3 stages of aerobic respiration_

_*Explain each of the steps in the Citric Acid Pathway (actual pathway given in exam)_

STAGE 2

Describe RXN 5

A
  • Catalysed by succinyl CoA synthetase
  • Substrate-level phosphorylation
  • High e bond of succinyl-CoA is cleaved, forming succinate
  • Coenzyme A regenerated
  • GTP (ATP) synthesis coupled w/ e released from breaking of thioester bond b/w succinate => CoA
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12
Q

_​*Define cellular respiration & ID 3 stages of aerobic respiration_

_*Explain each of the steps in the Citric Acid Pathway (actual pathway given in exam)_

STAGE 2

Describe RXN 6

A
  • Catalysed by succinate DH
  • Dehydrogenation, oxidation rxn
  • 1st oxidation 2H atoms removed from adjacent C atoms, producing C=C
  • Electrons are always accepted by FAD, which is reduced to FADH
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13
Q

_​*Define cellular respiration & ID 3 stages of aerobic respiration_

_*Explain each of the steps in the Citric Acid Pathway (actual pathway given in exam)_

STAGE 2

Describe RXN 7

A
  • Catalysed by fumarase
  • Hydration rxn
  • Fumarate hydrated to L-malate. H2O added across C=C
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14
Q

_​*Define cellular respiration & ID 3 stages of aerobic respiration_

_*Explain each of the steps in the Citric Acid Pathway (actual pathway given in exam)_

STAGE 2

Describe RXN 8

A
  • Catalysed by malate DH
  • Dehygrogenation rxn
  • NAD+ linked oxidation of alcohol group in malate
  • ∆G˚ strongly favours malate production -but proceeds to R due to removal of oxaloacetate by highly exergonic rxn 1 to produce citrate
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15
Q

_*Describe the major controls operating on pyruvate DH & the CC cycle_

Where does regulation generally occur?
Which four enzymes does it involve?

A
  • Occurs @ points of irreversible rxns
  • Involves:
  • **-Pyruvate DH complex
  • Citrate synthase
  • Isocitrate DH
  • a-ketoglutarate DH***
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16
Q

_*Describe the major controls operating on pyruvate DH & the CC cycle_

Describe Pyruvate DH complex regulation (link rxn)
Draw diagram on sl 57

A
  • Inhibited by high e levels
  • ATP
  • Acetyl-CoA
  • NADH
  • FA
  • Stimulated by low e levels
  • AMP
  • Coenzyme A
  • NAD+
17
Q

_*Describe the major controls operating on pyruvate DH & the CC cycle_

Describe Citrate Synthase regulation

A
  • Inhibited by high e levels
  • ATP
  • Succinyl-CoA
  • NADH
  • Citrate
  • Stimulated by low e levels
  • ADP
18
Q

_*Describe the major controls operating on pyruvate DH & the CC cycle_

Describe Isocitrate DH regulation

A
  • Inhibited by high e levels
  • ATP
  • Stimulated by low e levels
  • ADP
19
Q

_*Describe the major controls operating on pyruvate DH & the CC cycle_

Describe a-ketoglutarate regulation

A
  • Inhibited by high e levels
  • Succinyl-CoA
  • NADH
20
Q

_*Understand that the irreversible nature of the citric acid cycle means that there cannot be a next synthesis of glucose from acetyl-CoA_

Why?

A
  • Significant when fats are used as fuels
  • Oxidation of FA’s yield acetyl-CoA
  • because link rxn is irreversible, acetyl-CoA must be fed into CA cycle
  • :: cannot be used to synthesise glucose
21
Q

Acetyl-CoA (2C) oxidised two CO2 molecules. Energy released from these molecules is stored as?

A
  • GTP
  • NADH
  • FADH2
22
Q

What are the 3 irreversible reactions of the CA cycle?

A
  • RXN 1: one oxaloacetate condenses w/ acetyl-CoA
  • RXN 3 & 4: Two CO2 released
23
Q

How many reactions in the CA cycle are catalysed by dehydrogenases?

A

4

24
Q

Energy released by oxidation of acetyl-CoA in the CA cycle is conserved in the production of….?

A 
3 NADH & 1FADH2
1 GTP (ATP)
25
Q
A
  1. Glucose oxidation under anaerobic conditions yields 2 ATP; under aerobic conditions yields 30-32 ATP
26
Q
A
  1. Thyamine pyrophosphate, lipolic acid and NAD+
27
Q
A
  1. Reaction 5
28
Q
A
  1. Reactions 3 & 4
29
Q
A
  1. Fumarate
30
Q
A
  1. 1 mol of FADH2
31
Q
A
  1. 4 mol of NADH, 1 mol of FADH2, 1 mol of GTP
32
Q
A
  1. Acetyl-CoA
33
Q
A
  1. a-ketoglutarate to succinyl-CoA
34
Q
A
  1. Succinyl-CoA to succinate
35
Q

Look at CA cycle diagram.
Which are the intermediates?
How many carbons do they have?

A

acetyl-coa = 2C

Citrate = 6C

Isocitrate = 6C

a-ketoglutarate = 5C

Succinyl-CoA = 4C

Succinate = 4C

Fumarate = 4C

Malate = 4C

Oxaloacetate = 4C

36
Q

Draw a flow chart of the CAC indicating what type of rxn occurs at each of the 8 steps

A
  1. Condensation
  2. a) Dehydration b) Hydration
  3. Oxidative decarboxylation
  4. Oxidative decarboxylation
  5. Substrate level phosphorylation
  6. Dehydrogenation
  7. Hydration
  8. Dehydrogenation

BCM210 (18 decks)

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