Download - Cellular respiration - Krebs Cycle
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Part 2: Oxidative Decarboxylation, Krebs
Cellular Respiration
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Recall: Location
Glycolysis occurs in the cytoplasm
Krebs cycle occurs in the matrix
The end product of glycolysis (pyruvate) must make its way into the mitochondria
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Oxidative Decarboxylation
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Pyruvate Oxidation / Oxidative Decarboxylation Decarboxylation Redox reaction Coenzyme A addition
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Oxidative DecarboxylationPyruvate (3C) is converted into acetyl-
CoA (2C) in order to be brought into the mitochondria
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Oxidative Decarboxylation
Reaction type: decarboxylatio
n redox synthesis
Enzyme: decarboxylase dehydrogenase synthase
Energy: released
CYTOSOL MITOCHONDRION
NADH + H+NAD+
2
31
CO2 Coenzyme APyruvate
Acetyl-CoA
S CoA
C
CH3
O
Transport protein
O–
O
O
C
C
CH3
Figure 9.10
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Coenzyme A
Coenzyme A is a large organic molecule
Active functional group is a thiol
also written as CoA-SH
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Oxidative Decarboxylation Summary2 pyruvate 2 acetyl-CoA
2 CO2 released
2 NADH produced
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Krebs Cycle
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Krebs Cycle
Also known as the citric acid cycle (CAC) and the tricarboxylic acid cycle (TCA)
Krebs cycle is a cyclical process to:generate more high energy
molecules (NADH, FADH2 and ATP)produce additional CO2 molecules
(byproducts)
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Citric Acid Cycle OverviewFor each turn of
Krebs cycle: two carbons exit
completely as CO2 three NADH and one
FADH2 are formed One ATP is made by
substrate-level phosphorylation
ATP
2 CO2
3 NAD+
3 NADH
+ 3 H+
ADP + P i
FAD
FADH2
Citricacidcycle
CoA
CoA Acetyl-CoA
NADH+ 3 H+
CoA
CO2
Pyruvate(from glycolysis, 2 molecules per glucose)
ATP ATP ATP
Glycolysis Citricacidcycle
Oxidativephosphorylatio
n
Figure 9.11
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Figure 9.12
Krebs Cycle
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Krebs Cycle: Step by Step
Step 1: join 2 carbon molecule
with a 4 carbon molecule
Recycling of CoA
reaction type: synthesis
enzyme: synthase
energy: absorbed
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Krebs Cycle: Step by Step
Step 2: rearrangement of
atoms with the help of H2O
reaction type: isomerization
enzyme: isomerase energy: equilibrium
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Krebs Cycle: Step by Step
Step 3: synthesis of CO2 and
NADH 6C 5C reaction type:
decarboxylation redox
enzyme: Decarboxylase dehydrogenase
energy: released
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Krebs Cycle: Step by StepStep 4: synthesis of CO2 and NADH 5C 4C CoA returns reaction type:
decarboxylation redox synthesis
enzyme: decarboxylase dehydrogenase
energy: released
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Krebs Cycle: Step by Step
Step 5: ADP phosphorylation to ATP CoA recycled Reaction type:
substrate-level phosphorylation
Cleavage enzyme:
kinase lyase
energy: released
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Krebs Cycle: Step by Step
Step 6: FADH2 (energy
molecule) formation reaction type:
redox enzyme:
dehydrogenase energy: released
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FAD / FADH2
FAD – flavin adenine dinucleotide (oxidized form)
FADH2 – flavin adenine dinucleotide (reduced form)
Acts the same way as NAD+ NADH by accepting electrons
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FAD / FADH2
FAD – flavin adenine dinucleotide (oxidized form)
FADH2 – flavin adenine dinucleotide (reduced form)
Acts the same way as NAD+ NADH by accepting electrons
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Krebs Cycle: Step by Step
Step 7: rearranging the
molecule for the next reaction
reaction type: hydration
enzyme: hydrase
energy: absorbed
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Krebs Cycle: Step by Step
Step 8: energy molecule
formation & recreating molecules for Krebs cycle
reaction type: redox enzyme:
dehydrogenase energy: released
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Krebs Cycle Summary two cycles of Krebs for EACH glucose
molecule acetyl-CoA oxaloacetate (per cycle) 2 CO2 released (per cycle) 3 NADH produced (per cycle) 1 FADH2 produced (per cycle) 1 ATP produced (per cycle)
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Krebs Cycle