Download Preparation of pyruvate for the citric acid cycle Recap 1. We have

Preparation of pyruvate for the citric acid cycle
Recap
1.
2.
3.
We have worked our way through glycolysis
We now have 2 molecules of pyruvate
We have produced 2 ATPs and 2 NADHs
We have already stated what happens to pyruvate:
Aerobic conditions
1. Converts to acetyl CoA (by pyruvate dehydrogenase) for use in the TCA cycle and
oxidative phosphorylation (leads to more ATP production)
2. Converts to oxaloacetate , which can then shuttle into the synthesize glucose (can also
be done from lactate)
Anaerobic conditions
3. It is converted to Lactate (animal muscles)
4. It is converted to ethanol (yeast; alcohol fermantation)
Pyruvate enters the Citric acid cycle
First, we need to get pyruvate to the correct location:
Glycolyis occurs in the ______________
TCA cycle occurs in the ______________
Mitochondria
1. Recall that mitochondria have 2 membranes
2.
The outer mitochondrial membrane is permeable to most small molecules (transport occurs by
diffusion)
3.
The inner mitochondrial membrane is impermeable to most molecules
(transport requires active or symport transport)
4.
Pyruvate is transported into the mitochondria by pyruvate translocase
(an integral membrane protein that drives the movement of pyruvate by symporting it with H+)
Chemistry C483
Fall 2009
Prof Jill Paterson
31-1
Conversion of pyruvate to acetyl CoA
In order to enter the citric acid cycle, pyruvate must be converted to acetyl CoA
This occurs by oxidative decarboxylation of pyruvate (with the release of CO2).
A reaction catalyzed by pyruvate dehydrogenase.
+ H+
Pyruvate dehydrogenase contains 36 subunits!!!!
36 subunits include:
• 3 enzymes
E1: pyruvate dehydrogenase
E2: dihydrolipoamide acetyltransferase
E3: dihydrolipoamide dehydrogenase
• 5 coenzymes
• other proteins
TPP
CoASH
FAD & NAD+
Pyruvate dehydrogenase: Step 1
E1:
Pyruvate dehydrogenase: Step 2
E2:
Chemistry C483
Fall 2009
Prof Jill Paterson
31-2
Pyruvate dehydrogenase: Step 3
E2:
Pyruvate dehydrogenase: Step 4
E2:
Pyruvate dehydrogenase: Step 5
E3:
E3-FADH2 + NAD+
E3-FAD + NADH + H+
But now pyruvate is ready to enter the citric acid cycle!
It has been converted to Acetyl CoA…
We can also get acetyl CoA from:
the metabolism of fatty acids
the metabolism of amino acids
Chemistry C483
Fall 2009
Prof Jill Paterson
31-3
Additional ways to enter the TCA cycle
Chemistry C483
Fall 2009
Prof Jill Paterson
31-4