Cell Metabolism 2 - Tricarboxylic Acid Cycle Flashcards
Products of the Kerbs/TCA cycle
2x CO2
3x NADH
1x GTP
1x FADH2
Where is the Krebs/TCA cycle located?
Mitochondrial matrix space
When is the bulk of ATP generated?
When reduced coenzymes are re-oxidised
Step 1:How does the Krebs/TCA cycle start?
Acetyl CoA joins with oxoaloacetate —> makes citrate
Condensation of 4C + 2C
Step 2: what happens to citrate
Isomerise to isocitrate
Step 3: what happens to the isocitrate?
Isocitrate —> alpha ketoglutarate
Decarboxylation
Removes e- —> added to NAD+ to form NADH
Step 4: what happens to alpha-ketoglutarate?
Alpha-ketoglutarate —> succinyl-CoA
Decarboxylation
Removes e- —> added to NAD+ to form NADH
Step 5: what happens to succinyl CoA?
Succinyl CoA —> succinate
Removes CoA-SH
GDP + Pi —> GTP
Step 6: what happens to succinate?
Succinate —> fumerate
Removes e- —> added to FAD —> FADH
Step 7: what happens to fumerate?
Fumerate —> malate
Hydration
Step 8: what happens to malate?
Malate —> oxoloacetate
Removes e- —> NAD+ —> NADH
What does oxaloacetate do?
Joins with another acetyl CoA
Why is FAD used rather than NAD?
Free energy change is only enough to be able to reduce FAD
FAD has a greater affinity to the e-
What two types of amino acids enter the TCA cycle?
Glucogenic
Ketogenic
What happens to an amino acid before it is fed into the TCA cycle?
Amino acid removed —> excreted as urea
Carbon skeleton funnelled into the the TCA cycle
What is transamination?
Amine group is transferred from one amino acid to a keto acid
Group transfer
Alainine transamination
Alanine + alpha-ketoglutarate —> pyruvate + glutamate
Glutamate re-converted into alpha-ketoglutarate by glutamate dehydrogenase
How many ATP does NADH, FADH, GTP?
3
2
1
How does NADH (its high energy e-) cross from the cytoskeleton into the mitochondria matrix?
Glycerol phosphate shuttle
Malate-aspartame shuttle
What happens in the glycerol phosphate shuttle?
Dihydroxyacetone phosphate converted into glycerol 3-phosphate
NADH transfers e- to DHAP
Membrane bound glycerol 3-phosphate transfers e- to FAD to from FADH2
Where does the glycerol phosphate shuttle occur?
Muscle
Brain
What happens in the malate-aspartate shuttle?
Aspartate ate converted into oxoalacetate ( transamination)
Oxoalacetate converted into malate
NADH gives e- to malate
Malate diffuses through the mitochondrial matrix
Reverse reactions happen
NAD+ —> NADH
Where does the malate-aspartate shuttle occur?
Liver
Heart
Kidney
How many ATPs does the oxidation of 1x acetyl CoA give?
3x NADH (3x3)
1x FADH2 (1x2)
1x GTP
(3x3) + (1x2) + 1 = 12 ATP
What do mutations in the TCA cycle genes cause?
Decrease TCA activity and enhance aerobic glycolysis (Warburg Effect)
