The Citric Acid Cycle Flashcards
Where does the citric acid cycle happen
In the mitochondrial matrix
How does the citric acid cycle begin
The two carbon acetyl CoA from the bridge reaction reacts with oxaloacetate (4c) from gluconeogensis
How much co2 and atp is made in TCA
2 co2
1 atp
How much NADH and FADH2 is made in TCA
What does each do
3 NADH
1 FADH2
They carry total 8 electrons by getting reduced
What is stage 1 of TCA
Reactions 1-4 where two carbon atoms are oxidized and energy rich electrons are gathered
What is stage 2 of TCA
Reactions 5-8 where oxaloacetate is regenerated
one atp is made
energy rich electrons are gathered
What enzyme catalyzed stage 1 of TCA
What does it do
Citrate synthase
Condensation reaction where acetyl CoA (4c) and oxaloacetate (2c) are joined together
This makes citryl CoA (6c) intermediate
After the 6c citryl CoA intermediate is made what happens
Hydrolysis where the CoA leave and H2O comes in
Makes citrate in the end (6C)
In what way does the enzyme citrate synthase interact to make citrate
Is an ordered sequential reaction where oxaloacetate binned to the enzyme and acetyl CoA then the two products leave
It changes it’s confirmation when oxaloacetate binds then when citryl CoA if formed (induced fit)
After citrate is made what enzyme catalyzes the second reaction of the TCA
What type of enzyme is it
Acotinase
A Lyase (it removes and form double bonds)
What does acotinase do in the second reaction of TCA
Citrate is dehydrated (H and oh removed)
This forms cis-aconitate
Then cis aconitate is hydrated (add h and oh)
This makes isocitrate
What is the purpose of the second reaction of TCA
It’s an isomerization reaction where the tertiary oh of citrate is turned into the 2 oh in isocitrate
This part prepares for the next reaction oxidative decarboxylation
What is the enzyme that catalyzes the third reaction of TCA
Isocitrate dehydrogenase
What does isocitrate dehydrogenase do in the third reaction of TCA
Isocitrate (6 carbons) is oxidized (loses two H) which make NADH and oxalosuccinate (6c)
Oxalosuccinate is decarboxylated (lose co2)
This forms alpha-keto glutarate (a ketone and a carboxylic acid)
What catalyzes the 4th reaction of TCA
Alpha keto glutarate dehydrogenase complex
What does the Alpha keto glutarate dehydrogenase complex do in the 4th reaction of the TCA
Alpha keto glutarate (5c) is decarboxylated then oxidized
The CoA bind to it via a thioester bond and forms succinyl CoA (4c), co2 and NADH
Like the pyruvate dehydrogenase complex (same enzymes coafotores and e3 is identical)
From steps 1 to 4 of the TCA, how many electron are gathered
Nadh was formed two times
Each Nadh takes take electrons to make
4 electrons
On stage 2 of TCA what enzyme catalyzed the 5th reaction
Succinyl CoA synthetase
What does Succinyl CoA synthetase do in the 5th TCA reaction in stage two
Succinyl CoA does substrate level phosphorylation to turn adp to atp
The thioester bond is cleaved to make the atp, The CoA group on the Succinyl CoA leaves
This forms CoA, atp, and succinate
Slide 16
Do we need to. Know diagaram
What enzyme catalyzed the 6th reaction in stage two of TCA
Succinate dehydrogenase
What does Succinate dehydrogenase do in the 6th reaction of TCA
succinate is oxidized and forms fumarate and FADH2 (not Nadh because not enough energy to do that reaction)
What is special about succinate dehydrogenase
Unlike all the other enzymes, succinate dehydrogenase is not is the matrix.
It is part of the electron transport chain in the inner mitochondria membrane
What enzyme catalyzes the 7th reaction of TCA and what happens
Fumarase (Lyase)
Fumarate is hydrated (h and oh added)
This forms malate
What enzyme catalyzes the 8th reaction of TCA and what happens
Malate dehydrogenase
Malate( 4c) is oxidized to form NADH and regenerates oxaloacetate (4c)
What is the delta g of the 8th step of TCA and what does it mean
39.7kj/mol
The reaction is exergonic and happens in the forward direction to reuse oxaloacetate for the next reaction
What are the net products of the TCA
2 CO2, 3 NADH, fadh2, ATP, 2H, CoA
What two enzymes are regulated in TCA
Isocitrate dehydrogenase
Alpha ketoglutarate dehydrogenase
How is Isocitrate dehydrogenase regulated
If inhibited what happens
Is allosterically stimulated by adp
Inhibited by atp and Nadh
If inhibited, there’s more citrate with then goes to inhibit phosphofructokinase from glycoslis
How is Alpha ketoglutarate dehydrogenase regulated
Atp inhibits it
It’s products inhibited it (negative feedback)
Slide 25
Idk
How is oxaloacetate also replenished other then in the TCA
It’s made in gluconeogensis
Pyruvate carboxylase enzyme turns pyruvate to oxaloacetate through adding a co2
This is called an anaplerotic reaction (where is fill up the pathway with oxaloacetate)
What does the anaplerotic reaction require
How is it regulates
Acetyl CoA
If the energy charge (atp) is high, glucose is made (no gluconeogensis to make oxaloacetate)
If low TCA is run because gluconeogeneis is happening
