Carbon Skeletons of Amino Acids - Essentials
essentials of carbon skeletons
- Via glycolysis, glucose (6C) converts to pyruvate (3C), which can then degrade to acetyl CoA (2C).
In animals, there is NO pathway back from acetyl CoA to pyruvate.
- Via gluconeogenesis, pyruvate converts to oxaloacetate (4C) and on to phosphoenolpyruvate, which (through a series of reactions) converts back to glucose.
Thus, although gluconeogenesis results in the formation of glucose from pyruvate, it is NOT simply the reverse of Glycolysis.
- Acetyl coA can either undergo ketogenesis and form ketone bodies and free fatty acids (FFA).
- OR it can enter the TCA cycle where its 2 carbons combine with oxaloacetate's 4 carbons to form citrate (6C).
It would seem like this would then allow acetyl CoA to send its carbons around the cycle and generate glucose from them BUT show that these carbon molecules are used up in are used up in decarboxylation reactions.
– Thus, acetyl CoA can't re– generate pyruvate via the Kreb's cycle.
– The importance of this can't be overstated: Animals cannot generate glucose from ketone bodies or free fatty acids.