Question

5. What steps must be taken before each of the following biological molecules can be oxidized for the generation of ATP? How and where do these alternate fuels enter the cellular respiration pathway that we saw for glucose? Glycogen a. b. Triacylglycerol adt c. Protein nole er 1te

Answer 1

Ans - a. Glycogen - Excess glucose in the blood is stored in the form of glycogen in muscles and liver. When the blood sugar level drops this stored glycogen is utilized as the substrate for cellular respiration. Glycogen enters in cellular respiration as Glucose - 6 phosphate after glycolysis step.

b. Triacylglcerol - It consists of 1 molecule of glycerol and 3 fatty acids molecule which enter in cellular respiration pathway at different steps. Fatty acids undergo beta oxidation to form acetyl co-A while glcerol changes to glyceraldehyde - 3 phosphate before entering cellular respiration pathway.

c. Protein - Proteins are used as substrate for cellular respiration only in case of extreme starvation of cell. It is first broken down into amino acids and the step involves the removal of amino group. Each amino acid enters differently in the TCA cycle . For e.g - isoleucine changes to acetyl co- A and enters in the first step, asparagine converts to oxaloacetate and enters in the last step, tyrosine and phenylalanine enters as fumarate in the sixth step, histidine , proline, glutamine ,arginine change to glutamate and further to alpha ketoglutarate before entering in the third step, serine, cysteine, alanine enter as pyruvate .