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Krebs cycle

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Title: PowerPoint Presentation Author: Pat Ballow Last modified by: Patricia Ballow Created Date: 10/7/2007 8:18:26 PM Document presentation format – PowerPoint PPT presentation

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Title: Krebs cycle


1
Krebs cycle
2
Krebs Cycle (Citric acid cycle)
  • Series of 8 sequential reactions
  • Matrix of the mitorchondria
  • Synthesis of 2 ATP
  • Generation of 8 energetic electrons
  • 4 CO2 molecules

3
Krebs Cycle
4
Reaction 1 Condensation
  • 2-carbon acetyl group from acetyl-CoA
  • Joins with oxaloacetate a four-carbon molecule
  • Forms a six-carbon molecule, citrate.

5
Reaction 2 Isomerization
  • Hydroxyl (-OH) group of citrate is repositioned
  • A water molecule is removed from one carbon
  • Water is added to another carbon on the same
    citrate molecule.
  • As a result, an H group an OH group change
    positions.
  • Product is isocitrate-an isomer of citrate

6
Reaction 3 The First Oxidation
  • First energy yielding step of cycle
  • Isocitrate undergoes an oxidative decarboxylation
    reaction.
  • First isocitrate is oxidized
  • Yielding a pair of electrons
  • Associated with a proton as a hydrogen atom
  • Reduces NAD to NADH.

7
Reaction 3 The First Oxidation
  • Second oxidized intermediate is decarboxylated
  • Central carbon atom splits off to form CO2
  • Yields a five-carbon molecule
  • a-ketoglutarate

8
Reaction 4 The Second Oxidation
  • a-ketoglutarate is decarboxylated
  • Looses a CO2
  • CoEnzyme A is attached
  • Forms succinyl-CoA
  • Two electrons are extracted
  • Associated with a proton as a hydrogen atom
  • Reduce another molecule of NAD to NADH.

9
Reaction 5 Substrate-Level Phosphorylation
  • Linkage between the four-carbon succinyl group
    CoA is a high-energy bond.
  • Bond is cleaved
  • Energy released drives phosphorylation of GDP,
    forming GTP.
  • GTP is readily converted into ATP,
  • Succinate 4-carbon fragment that remains

10
Reaction 6 Third Oxidation
  • Succinate is oxidized to fumarate
  • FAD is electron acceptor.
  • FAD remains in a part of the inner mitochondria
    membrane
  • FADH2 (reduced) is used in electron transport
    chain in the membrane

11
Reactions 7 8 Regeneration of Oxaloacetate.
  • A water molecule is added to fumarate,
  • Forms malate
  • Malate is then oxidized
  • Yields oxaloacetate a four-carbon molecule
  • Two electrons
  • Associated with a proton as a hydrogen
  • Reduce a molecule of NAD to NADH.

12
Reactions 7 8 Regeneration of Oxaloacetate.
  • Oxaloacetate
  • Molecule that began the cycle
  • Combines with another two-carbon acetyl group
    from acetyl-CoA
  • Reinitiate the cycle.

13
Fig. 9-12-1
Acetyl CoA
CoASH
1
Oxaloacetate
Citrate
Citric acid cycle
14
Fig. 9-12-2
Acetyl CoA
CoASH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Citric acid cycle
15
Fig. 9-12-3
Acetyl CoA
CoASH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric acid cycle
NADH
3
H
CO2
?-Keto- glutarate
16
Fig. 9-12-4
Acetyl CoA
CoASH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric acid cycle
NADH
3
H
CO2
CoASH
?-Keto- glutarate
4
CO2
NAD
NADH
H
Succinyl CoA
17
Fig. 9-12-5
Acetyl CoA
CoASH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric acid cycle
NADH
3
H
CO2
CoASH
?-Keto- glutarate
4
CoASH
5
CO2
NAD
Succinate
NADH
P
i
H
Succinyl CoA
GDP
GTP
ADP
ATP
18
Fig. 9-12-6
Acetyl CoA
CoASH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric acid cycle
NADH
3
H
CO2
Fumarate
CoASH
?-Keto- glutarate
4
6
CoASH
5
FADH2
CO2
NAD
FAD
Succinate
NADH
P
i
H
Succinyl CoA
GDP
GTP
ADP
ATP
19
Fig. 9-12-7
Acetyl CoA
CoASH
H2O
1
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric acid cycle
NADH
3
H
7
H2O
CO2
Fumarate
CoASH
?-Keto- glutarate
4
6
CoASH
5
FADH2
CO2
NAD
FAD
Succinate
NADH
P
P
i
Succinyl CoA
H
GDP
GTP
ADP
ATP
20
Fig. 9-12-8
Acetyl CoA
CoASH
NADH
H2O
1
H
NAD
Oxaloacetate
8
2
Malate
Citrate
Isocitrate
NAD
Citric acid cycle
NADH
3
H
7
H2O
CO2
Fumarate
CoASH
?-Keto- glutarate
4
6
CoASH
5
FADH2
CO2
NAD
FAD
Succinate
NADH
P
i
H
Succinyl CoA
GDP
GTP
ADP
ATP
21
Krebs Cycle
  • 2 pyruvate from glycolysis
  • 6 CO2 molecules
  • 2 ATP molecules
  • 10 electron carriers
  • 8 NADH molecules
  • 2 FADH2

22
Figure 9.16b
6 NADH
2 FADH2
2 NADH
PYRUVATE OXIDATION 2 Acetyl CoA
CITRIC ACID CYCLE
2 ATP
23
  • Glycolysis the Krebs cycle
  • produced a large amount of electron carriers.
  • These carriers enter the electron transport chain
  • Help produce ATP

24
Electron transport chain
  • Energy captured by NADH is not harvested all at
    once.
  • Transferred directly to oxygen
  • 2 electrons carried by NADH are passed along the
    electron transport chain if oxygen is present.

25
Oxidative phosphorylation Formation of ATP
  • 1. Electron transport chain
  • Series of molecules embedded in the inner
    membranes of mitochondria.
  • Electrons are delivered at the top of the chain
  • Oxygen captures them at the bottom

26
Electron transport chain
  • Large protein complexes
  • Smaller mobile proteins
  • Smaller lipid molecule called ubiquinone (Q)

27
Fig. 9-13
NADH
50
e
2
NAD
FADH2
2
e
FAD
Multiprotein complexes
?
FAD
40
FMN
??
FeS
FeS
Q
???
Cyt b
FeS
30
Cyt c1
IV
Free energy (G) relative to O2 (kcal/mol)
Cyt c
Cyt a
Cyt a3
20
e
2
10
(from NADH or FADH2)
O2
2 H 1/2
0
H2O
28
  • Electrons move towards a more electronegative
    carrier
  • Electrons move down an electron gradient
  • This flow of electron creates the active
    transport of protons out into the matrix

29
  • 2. Chemiosmosis
  • Protons diffuse back into the matrix through a
    proton channel
  • It is coupled to ATP synthesis

30
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31
Electron transport chain
  • Carbon monoxide cyanide affect the electron
    transport in the mitochondria
  • Shuts down the production of ATP
  • Cell dies as does the organism

32
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33
Fermentation
  • Anaerobic conditions
  • H atoms (NADH) are donated to organic compounds
  • Regenerates NAD

34
Figure 9.17a
2 ADP 2
P
2
ATP
i
GLYCOLYSIS
Glucose
2 Pyruvate
NAD
NADH
2
2
2
CO2
2 H
2
Ethanol
2 Acetaldehyde
(a)
Alcohol fermentation
35
Figure 9.17b
2
2 ADP 2
ATP
P
i
GLYCOLYSIS
Glucose
NAD
2
2
NADH
2 H
2 Pyruvate
Lactate
2
(b)
Lactic acid fermentation
36
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37
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38
Proteins and fats
  • Other organic molecules are an important source
    of energy.

39
Proteins
  • First are broken down to amino acids
  • Each amino acid undergoes a process called
    deamination.
  • Removal of the nitrogen containing side group
  • After a series of reactions the carbon groups
    enter the either glycolysis or the krebs cycle

40
Fats
  • Fats are broken down to FA glycerol
  • Each FA undergoes ß oxidation
  • Conversion of the FA to several acetyl groups
  • These groups combine with coenzyme A to make
    acetyl-CoA

41
Regulation
  • Control of the glucose catabolism
  • Occurs at 3 key points
  • 1. Control point in glycolysis
  • Enzyme phosphofructokinase
  • Catalyzes the conversion of fructose 6-phosphate
    to fructose 1,6 bisphosphate.

42
Regulation
  • High levels of ATP inhibit phosphofructokinase
  • ADP AMP activate the enzyme
  • Low levels of citrate also activate the enzyme

43
Regulation
  • 2. Pyruvate dehydrogenase
  • Enzyme that removes CO2 from pyruvate.
  • High levels of NADH will inhibit its action

44
Regulation
  • 3. High levels of ATP inhibit the enzyme citrate
    synthetase
  • Enzyme that starts the Krebs cycle
  • Combines Acetyl-CoA with oxaloacetate to make
    citrate

45
Evolution
  • Krebs cycle ETC function only in aerobic
    conditions
  • Glycolysis occurs in both
  • Early bacteria used only glycolysis to make ATP
    before O2
  • All kingdoms of life use glycolysis
  • Occurs outside the mitochondria
  • Indicates mitochondria developed later.
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