L16- The Citric Acid Cycle Flashcards
Where does it take place?
In mitochondria in eukaryotes or cytosol in bacteria
What are the intermediates used for?
Biosynthetic reactions
It’s aerobic catabolism, meaning which type of reactions?
Oxidation reactions
How is energy in the citric acid cycle largely stored as?
Reducing power
Which co-enzymes are reduced? To what?
- NAD+ –> NADH
- Ubiquimome (Q) –> Ubiquinol (QH2)
how does pyruvate get into the mitochondria?
It’s transported by pyruvate translocase, in symport with H+.
What happens once pyruvate has enetered the mitochondria?
Pyruvate is then coupled to coenzymes A and decarboxylated and oxidised by a huge enzyme complex called pyruvate dehydrogenase.
In summary, what is done for each acetyl coA which enters the cycle?
- Two molecules of CO2 are released
- Coenzymes NAD+ and Q are reduced
- One GDP (ADP) is phosphorylateed
- The intitial acceptor molecule (oxoloacetate) is reformed
How can reduced coenzymes make ATP?
NADH+, QH2 can be oxidised to produce ATP by oxidative phosphorylation
For each acetyl coA entering the cycle, what is the net production of energy stores?
3 NADH
QH2
GTP (or ATP)
How many ATPs does the oxidation of each yield?
- NADH
- QH2
- Acetyl CoA (complete oxidation)
- 2.5 ATP
- 1.5 ATP
- 10 ATP
how many ATP molecules are made during:
- substrate level phosphorylation
- Oxidative phosphorylation
- 4
- 28
Total = 32
Glycolytic NADH is available to fuel ATP formation. How can ir be transferred to the mitochondria?
- most common- Malate aspartate shuttle
- Glycerol phosphate shuttle (yields one fewer ATPs per NADH, 2 fewer in total, only 30)
What controls the citric acid cycle?
- allosteric modulators
- covalent modification of cycle enzymes
- supply of acetyl CoA
What regulates th pyruvate dehydrogenase complex PDH?
High levels of acetyl CoA and NADH inhibit the PDH. (feedback)
Phosphorylation of E1 by kinase (part of PDH) makes it inactive. Use phosphotase to take phosphate off, re-activates PDH complex.
