Carbohydrates 5: Citric Acid Cycle Flashcards
where does citric acid cycle occur?
mitochondrial matrix
what are 3 common “fuel” molecules?
- carbohydrates
- amino acids
- fatty acids
does the cycle produce ATP directly?
No
does the cycle include O2 as the reactant directly?
No
As electrons are formed, what two reduced electron carriers are produced?
NADH and FADH2
In which glycolysis step is the NAD converted to NADH ( reduction)
step 6
in which step in glycolysis is NADH re-oxidised? (to form NAD again)
Pyruvate to lactate step
what is citric acid cycle in simple words?
Stripping molecules from their electrons which are carried to terminal respiration step. Electrons are harvested to completely oxidise food molecules to CO2, H2O and make lots of energy
what 2 substances can be oxidised to form acetyl CoA?
- pyruvate (from glycolysis)
2. fatty acids
what enzyme is used to break down pyruvate into acetyl CoA?
pyruvate dehydrogenase
what 3 steps/ series of reactions occur when acetyl CoA is formed from pyruvate?
- decarboxylation of pyruvate
- oxidation
- transfer/attachment of CoA complex
what does the carboxylation step in formation of acetyl CoA from pyruvate release?
2 electrons (2H ions)
what electron carrier goes through reduction in the formation of acetyl CoA from pyruvate?
NAD turns to NADH (carries the 2 electrons released through pyruvate dehydrogenase)
what is pyruvate dehydrogenase made up of?
Many copies of each enzyme subunit
what is the advantage of having several enzyme subunits making up pyruvate dehydrogenase?
each subunit catalyses a different part of the reaction
what does E1 subunit in pyruvate dehydrogenase catalyse?
first decarboxylation of pyruvate
what does E2 subunit in pyruvate dehydrogenase catalyse?
transfers the acetyl group to coenzyme A
what does the E3 subunit in pyruvate dehydrogenase catalyse?
recycles lipoyllysine through reduction of FAD which is recycled by passing electrons to NAD+
why is CAC called the “black box”?
because intermediate molecules that make up the cycle remain CONSTANT at all times
what molecule is involved in energy transfer which is then readily converted to ATP?
GTP
what is the order of intermediates from CAC starting from citrate? (8)
- citrate
- isocitrate
- alpha-ketoglutarate
- succinyl-CoA
- Succinate
- fumarate
- malate
- oxaloacetate
what 2 molecules are released between isocitrate and alpha-ketoglutarate?
- NADH
- CO2
what 2 molecules are released between alpha-ketoglutarate and succinyl-CoA?
- NADH
- CO2
what is released at succinate intermediate
GTP
what is released between succinate and fumarate intermediates?
FADH2
what is release at oxaloacetate intermediate?
NADH
between which two steps in the CAC is CoA group removed completely?
between succinyl CoA and succinate steps
If the cell has enough energy, what will happen to the production of pyruvate dehydrogenase?
it will be stopped/ inhibited
what 3 things can inhibit pyruvate dehydrogenease that makes acetyl CoA
- ATP
- NADH
- acetyl CoA
what 2 things can stimulate production of pyruvate dehydrogenase to make acetyl CoA?
- ADP
- pyruvate
at what 2 intermediates in CAC, are the other control points?
- isocitrate
2. alpha-ketoglutarate
What sort of reactions are the control points in CAC?
non-reversible reactions (exergonic steps, deltaG -ve)
what 2 things inhibit isocitrate dehydrogenase?
- ATP
2. NADH
what stimulates isocitrate dehydrogenase?
ADP
what 3 things inhibit alpa-ketoglutarate dehydrogenase?
- ATP
- NADH
- succinyl CoA
are isocitrate and citrate interconvertible?
yes
if there is citrate build up when isocitrate dehydrogenase stops working, what happens?
citrate is shuttled into cytoplasm causing phosphofructokinase to stop glycolysis
what happens if there is a build up of alpha-ketoglutarate if alpha-ketoglutarate dehydrogenase is inactive?
alpha-ketoglutarate switches its use to production of amino acids
what sort of pathway is CAC?
amphibolic pathway (both catabolic and anabolic processes occur)
what does build up of citrate produce? (2)
fatty acids, sterols
what does build up of alpha-ketoglutarate produce?
- glutamate (leading to AAs like glutamine, proline, arginine etc) and purines
what does build up of succinyl CoA produce?
porphyrins, heme
what enzyme is used to convert pyruvate to oxaloacetate?
pyruvate carboxylase
what sort of a reaction is conversion of pyruvate to oxaloacetate?
anabolic process (formation)
what are the 3 main products produced as a result of intermediates from CAC building up?
- nucleotide bases
- heme groups
- proteins
if there is a build up of Acetyl CoA (excessive production) during exercise, what needs to be produced more of to keep CAC going?
oxaloacetate
what pathway can produce oxaloacetate directly?
Pyruvate can be converted to oxaloacetate through pyruvate carboxylase
what is the term given to conversion of pyruvate to oxaloacetate by pyruvate carboxylase?
anaplerotic
