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WHat does the CAC do?
What is it?
Where do the reactions take place?
oxidizes acetly groups from carbs, fatty acids, and amino acids
cycle (like one big enzyme)
all reactions in the mitochondria
What does the CAC do to carbons?
2 C in, 2 C out each cycle
intermediates are the building blocks
acetyl --> CO2, transfer 4 pair of electrons to 3 NADH and 1 FADH2, get 1 GTP
oxaloacetate+ acetyl coA--> citrate
catalyzed by citrate synthase (induced fit enzyme)
forms a 6 carbon structure that is needed to start the cycle
What is the structure of citrate synthase?
two active sites; two conformations
we don't want acetyl CoA to come in and have them hydrolyzed off. The enzyme helps this by remaining inactive until oxaloacetate binds; the active site closes. Acetyl CoA binds and 2 substrates are in the active site forming the substrate complex
From the substrate complex, an __ forms, and it is __.
In the citryl CoA complex, what happens?
- enol intermediate
- highly reactive and can allow condensation to take place
at this point, a 2nd conformation change takes place--> bond broken between citrate CoA
aconitase: via intermediate, you remove water, add water, etc.
In aconitase, what is involved?
iron is involved; in iron cluster: mutliple iron atoms cluster with sulfurs--> helps facilitate a reaction
4 Fe 4S cluster
In the step with isocitrate dehydrogenase, what happens?
- NADH forms
- isocitrate--> alpha ketoglutarate
it catalyzes oxidative decarboxylation
What is favorable with isocitrate dehydrogenase?
oxidation is favorable/ decarboxylation is not so much, coupling addition of O2 with removal of CO2
Alpha-ketoglutarate dehydrogenase complex
enzyme complex catalyzes this (a thioester bond)
electrons captured in NADH
this is teh 2nd oxidative decarboxylation
Succinyl CoA--> succinate
Where does the energy come from?
takes phosphate and GDP to become GTP
the energy comes in and energy from attaching succinate to CoA will supply nergy
An enzyme called __ can take GTP and ADP--> GDP and ATP
nucleoside diphosphate kinase
Explane succinate dehydrogenase
associated with the inner mitochondrial membrane and tghtly linked to ETC
- remove electrons
- --> energy not sufficient to form NADH--> so, FADH2 forms
adds water to convert Fumarate to malate
has enough electron transfer potential to form NADH
Final step of the pathway
Malate back to oxaloacetate by malate dehydrogenase
What was an experiment to identify if the same oxaloacetate is used?
They radioactively labeled terminal carbon on oxaloacetate. THough the molecule was symmetrical, the carbon that gets removed is the oxaloacetate one.
The reason for this is because, though it is symmetric, the enzyme is not and binds in a certain way that causes exposure of the carboxyl end of oxaloacetate, whch gets removed
What is the problem with oxaloacetate?
it is a building block of aspartic acid, asparagine, lysine, isoleucine, methionine, and threonine
So, it gets removed from the CAC. To restore the amounts that left, pyruvate gets converted to it by pyruvate carboxylase
gets converted to glutamate and then other amino acids and purines
intermediate that can be removed to make several amino acids
can be converted to porphyrins, heme, chlorophyll
2 succinyl CoA