L11: TCA cycle Flashcards
What is the energy cost of gluconeogenesis?
- 4 ATP
- 2 GTP
- 2 NADH
Where is ATP used in gluconeogenesis?
- Bypass 1 between pyruvate and oxaloacetate - uses 2 ATP as 2 molecules of pyruvate are used to produce 2 oxaloacetate
- Uses 2 ATP between 3-phosphoglycerate and 1,3-bisphosphoglycerate - 2 molecules of each so 2 ATP
Where is GTP used in gluconeogenesis?
- Bypass 1 between oxaloacetate and phosphoenolpyruvate
- 2 molecules of phosphoenolpyruvate generated so 2 GTP used
Where is NADH used in gluconeogenesis?
- Between 1,3-bisphosphoglycerate and glyceraldehyde-3-phosphate
- Uses 2 NADH as 2 glyceraldehyde generated
Is glycolysis or gluconeogenesis more energy expensive?
- Gluconeogenesis - uses 4 ATP, 2 GTP and 2 NADH
- Glycolysis uses 2 ATP, but produces 2 ATP and 2 NADH
Where does the TCA cycle take place?
Mitochondrial matrix
What conditions are required for the TCA cycle?
Aerobic conditions
What is the importance of the TCA cycle?
- Final common pathway for oxidation of fuel molecules: amino acids, fatty acids, carbohydrates
- Important supply of intermediates for biosynthesis - e.g. to generate nucleotides, amino acids and metabolites
- Important for production of energy
What molecule acts on pyruvate when it enters the mitochondria?
Pyruvate dehydrogenase (PDH)
What is pyruvate dehydrogenase?
- Multienzyme complex in the mitochondrial matrix
- Consists of 3 distinct enzyme - pyruvate decarboxylase (E1), dihydrolipoyl transacetylase (E2), dihydrolipoyl dehydrogenase (E3)
- Uses vitamin B1 as a cofactor
What is the main function of pyruvate dehydrogenase?
Catalyses the irreversible oxidative decarboxylation of pyruvate to produce acetyl CoA, CO2 (and NADH)
Where is pyruvate dehydrogenase found in the pathway for aerobic metabolism?
- Pre-Krebs
- Intermediate step before the Krebs cycle
Draw the mechanism for pyruvate into acetyl CoA. Include locations and molecules used and produced in the process
What important molecule is generated from the mechanism involving pyruvate dehydrogenase?
- 2 molecules of NADH
- No ATP here
What is energy requirements matching?
- When there is not enough glucose available to be metabolised, other sources of energy as used, including fatty acids and glycerols from fats, and amino acids from proteins in muscle cells
Draw the TCA cycle (to include the names of molecules, enzymes and what is generated)
- Citrate is a 6 carbon molecule
- a-ketoglutarate is a 5 carbon molecule
- Succinyl-CoA is a 4 carbon molecule
- Oxaloacetate is a 4 carbon molecule
What are the two parts to the TCA cycle?
- Control half - release of NADH and CO2
- Regeneration half - regenerate oxaloacetate to interact with another molecule of CoA to start the cycle again
What is the order in which you get production of NADH and energy equivalence in the TCA cycle?
- 2 Acetyl-CoA are used, as 2 pyruvate molecules are generated per glucose molecule so NADH and energy are double
- Means 2 ATP/GTP, 6 NADH, and 2 FADH2