Citric Acid Cycle Flashcards
How many enery capture steps in the CAC
5
What’s the first step of the CAC
- substrates + products/ enzymes/ irreversible or reversible
- first step is hydrolysis of the thioester bond
- irreversible conversion of A.Coa/OAA to citrate via the enzyme citrate synthase
What task does a synthase perform
joing 2 molecules together without ATP or NTP
Is the first step in the CAC exergonic or endergonic? Why
Exergonic, because of the release of energy of the thioester bond
What happens if there is an increase in citrate concentration?
the citrate is take to the cytosol to be used for Fatty acids
Why is citrate converted to isocitrate
because the tertiary hydroxyl group is hard to oxidized, so an isomerization occurs
what is the 3 steps of the CAC?
- important notes/ enzymes/ S&P/Rev or IRRev
- isocitrate is converted to A-ketoglutarate
- via a decarboxylation and oxidation
- Enzyme: Isocitrate dehydrogenase
- irreversible step
How does Mn2+ help with the decarboxylation of isocitrate
- it increases electron withdrawing group for decarboxylate
Where are the 2 forms of ioscitrate dehydrogenase and why do they reside there?
- Resides in the matrix of the mitochandria for CAC, NAD+ dependent enzyme
- Able to dump electrons onto NAD= - Resides in the cytosol for NADP+ dependent enzyme
Write the balanced equation of Isocitrates conversion
Isocitrate + NAD+ –> A Ketoglutarate + NADH + CO2
What makes pyruvate and A-KG, A-keto acids
They are 1 bond away from the carbonyl group making them a-keto acids
What cosubstrate is typically involved in the conversion of hydroxyl groups to carbonyl groups?
NAD+ and NADPH
What occurs in the 4th step of the CAC
- A-ketoglutarate is converted into Succinyl CoA
- enzyme: A-ketoglutarate dehydrogenase
- Irreversible step
- Thioester bond formed, decarboxylation and oxidation
What is complex is A-ketoglutarate dehydrogenase most similar to
PDH complex
How is A-ketoglutarate dehydrogenase regulated?
Via allostery
What are the difference between PDH and A-KG dehydrogenase?
what is the 5th step of CAC
- conversion of Succinyl-Coa to succinate
- transfer of thioester to high energy molecule
- SLP
- Succinyl-CoA synthetase
How does the energy capture step of succinyl-CoA occur
- Breaking of thioester bond to form an anhydride bond
Why does GDP need to be regenerated? How does this occur in the CAC
- has to be regenrated for reaction to work
- GDP is made into GTP which it transfers it Triphospate onto ADP making ATP via nuclotide diphosphate kinase
What do nucleotide diphosphate kinase do?
- transfer of phosphate
What does a synthetase do?
joins two molecules with the participation of ATP and NTP
How many high energy bonds in the Succinyl- CoA sythetase reaction?
4
Explain the succinyl- CoA synthetase reation
- Formation of succinyl phosphate
Pi + Succinyl- CoA(thioester) <-> succinyl-phosphate (mixed anhydride) + CoASH - Formation of phophoryl His
Enzymer-His + S.P <-> 3-phopho-His (phosphoamide) + Succinate - Phosphoryl tranfer to GDP forming GTP (SLP Step)
GDP + 3-phospho-His <-> GTP (phosphoanhydride)
What is the importance of the last 3 steps of the CAC?
they convert methylene group of Succinate to carbonyl group of OAA
Where does FAD typically show up in reactions
oxidations of alkanes to alkenes
What are the products of the Citric Acid Cycle?
3 NADH
1 GTP (ATP)
2 CO2
1 FADH2
Write a balanced equation for the CAC
A.CoA +3 NAD+ GDP + Pi + FAD H20 –> 2 CO2 + NADH + FADH2 + GTP + CoA
Why cant mammals convert FA into glucose?
Fatty acids are broken down into ACoA, there is no net gain of carbons therefore cannot be used as glucose
Where can FA’s enter in the CAC
As succinyl CoA, last 3 carbons of uneven fatty acids
What makes CAC an Amphibolic pathway?
- Catabolic processes such as oxidative catabolism of carbs, fa, and aa
- Anabolic process for aa syntheses, purine and pyrimidine biosynthesis, gluconeogensis, FA and sterol syntheisis
What processes in catapleurotic?
- OAA can be used for glucose
- Malate can be used for glucose
- Citrate for FA aand cholestrol
- A-KG for AA
Which processes are anapleurotic
- CO2, fatty acids for Succinyl- Coa
- Amino acids at A-KG
Why are anaplerotic reactions important in the CAC
- needed to replenish the CAC for anabolic process
What is the most important anaphlerotic process in mammales
pyruvate carboxylation
What transmination reaction occurs with pyruvate?
Alanine
What transmination reaction occurs with OAA?
Asparatate
What transmination reaction occurs with A-KG
glutamate
Under what conditions will pyruvate be turned into OAA?
- starvation
- Exercise
Under what conditions is pyruvate converted to A.CoA
Heavy fatty acids and amino acid metabolism
- acetyl CoA iacticates pyruvate carboxylase
Describe the process the occurs when during starvation, in regards to pyruvate?
- Occurs in the liver
- decrease in the PDC which converts Pyruvate to A.CoA
- A.CoA is converted to ketons which is used for fuel
- Increase in pyruvate carboxylate which converts pyruvate to OAA
What is the fate of pyruvate pyruvate during during exercise
- decrease in PDC
- Pyruvate is converted to OAA and used for the CAC
What are the most crucial factors the CAC responds to?
- Energy state of the cell (ATP:ADP)
- Redoc State of the cell
(NADH: NAD+)
Product inhibition of CA flux
- nadh
- succinyl-coa
- citrate
The activity of ETC controls…
the activity of the CAC
What occurs if there is a decrease in ADP in the mitochandria?
= D activity of ATp synthase, In. proton gradient, De E- flow, DE reoxidation of NADH, and Increase NADH: NAD+
What occurs if there is a increase in ADP in the mitochandria?
Increase ATP synthase activity, decreased proton gradient, increase electron flow, increase reoxidation of NADH and decreased NADH: NAD+
