Question

15. Where do the ketogenic amino acids enter the catabolic pathway (at what entry point)? answer here) 16. What TCA intermediate is needed to initiate the TCA cycle? n answer here) 17. What is the fate of acetyl-CoA as it enters the TCA cycle? answer here) 18. What is the fate of Coenzyme A after the TCA cycle? answer here) 19. What by-product(s) is/are produced in the TCA cycle? answer here) 20. Which coenzyme of TCA cycle is considered to be the primary co-enzyme? answer here) 21. Which coenzyme of TCA cycle is considered to be the secondary co-enzyme? answer here) 22. What is the name of the energy roduct of the TCA cycle?

help

Answer 1

15. The ketogenic amino acids enter the catabolic pathway at the point of oxidation of acetyl CoA, oxidative phosphorylation.

16. The TCA intermediate that is used to initiate the TCA cycle is acetyl CoA.

17. Four possible fates await the acetylCoA produced from fatty acids or glucose in the liver:

1. The acetyl CoA in the mitochondria may be oxidized to carbon dioxideand water in the citric acid cycle and respiration. This pathway, which isused if the liver cells need to generate energy through respiration, makesit clear that the citric acid cycle is shared by both glucose metabolismand fatty acid metabolism.

2. The acetyl CoA in mitochondria may be used to synthesize the sub-stances called ketonebodies. Some ketone bodies are oxidized for energyproduction by the liver. The remainder are transpofted to other tissuesthat can use them for energyproduction. Extensive production of ketonebodies from acetyl CoA occurs only when no glucose is available, as instarvation or diabetes. When no glucose is available to starving braincells, for example, they adapt to the use of ketone bodies as an energysource in about 48 hours.

3. The cltoplasmic acetyl CoA may be used to resynthesize fatty acids.Since some of the acetyl CoA may have come from glucose, this meansthat carbohydrates may be converted to fatty acids.

4. The acetyl CoA may be used to slnthesize cholesterol in the cellularcytoplasm. As with other synthetic processes, the slnthesis of fatty acidsand cholesterol occurs when the body is well supplied with energy.

19. Byproducts of TCA cycle :-

Citrate Synthase + acetyl CoA = citrate

N/A

Aconitase +H2O = isocitrate

N/A

Isocitrate dehydrogenase +NAD = alpha-keto-glutarate

+ CO2 + NADH + H

a-ketoglutarate dehydrogenase +NAD = succinyl-CoA +

aka 2-oxoglutarate dehydrogenase

+ CO2 + NADH + H

Succinyl-CoA dehydrogenase +GDP + Pi = succinate

+ GTP

Succinate dehydrogenase +FAD = fumarate

+ FADH2

Fumarase = malate

N/A

Malate dehydrogenase +NAD = oxoacetate

+ NADH + H