Question

31. A triglyceride, isolated from the seeds of a pumpkin, has the following fatty acid composition- 21:3, 28:7, 22:1. EITHER Calculate the theoretical energy yield in terms of ATPs, that could be obtained from the complete oxidation of the triglyceride and draw a flow diagram to show how you obtained the final number. OR Calculate the theoretical yield of glucose if two molecules of the triglyceride were converted to glucose. Draw a flow diagram to show how you obtained the final number. 32. Glutamine synthetase (GS) is one of the ways in which ammonia is incorporated into organic linkages. Briefly describe the reaction that GS catalyses and how the activity of GS in regulated in Escherichia coli. 33. Futile cycling is energetically wasteful to a cell. Briefly describe what you understand about futile cycling and, using at least two examples, describe how cells avoid it. What are the similarities and differences between the electron transport chains found in mitochondria and chloroplasts?

Answer 1

31.

32. Glutamine synthetase is an enzyme that condenses glutamate with ammonia to produce glutamine.Glutamine synthetase enzyme is regulated by different processes like adenylation/ deadenylation, uridinylation/ deuridinylation,

Adenylation by adenyl transferase enzyme deactivates the enzyme while deadenylation activates GS. A P₁₁ protein attached to UMP (by uridinylation of P₁₁) activates adenyl transferase enzyme.

33.

Futile cycle is also called substrate cycle. It is a process by which opposite metabolic reactions occur simultaneously resulting just in the dissipation of energy in the form of heat. For eg: If glycolysis and gluconeogenesis occur at the same time, glucose will be converted to pyruvate by glycolysis but glucose will be produced by gluconeogenesis. This results in simply utilization of ATP and waste of energy.

During glycolysis, fructose-6-phosphate is converted to fructose-1,6-bisphosphate in a reaction catalysed by the enzyme phosphofructokinase 1 (PFK-1).

ATP + fructose-6-phosphate ? Fructose-1,6-bisphosphate + ADP

and during gluconeogenesis,

Fructose-1,6-bisphosphate + H₂O ? fructose-6-phosphate + P_i

Giving an overall reaction of:

ATP + H₂O ? ADP + P_i + Heat

TO avoid futile cycles, cells have a) compartmentalization of the rate limiting steps in different cellular spaces b) irreversible steps for the enzyme requiring a separate enzyme for opposing step. c) difference in the regulation of enzyme involved in opposite reactions. d) utilization of different intermediates in different pathways.

Differences between the electron transport chain in mitochondria and chloroplast are

a) Mitochondria carry out oxidative phosphorylation whereas Chloroplasts use photophosphorylation for ATP synthesis

b) Mitochondria uses chemical energy from redox reactions in ETC whereas Chloroplasts utilizes light energy

c) In Mitochondria electron transport chain takes place in cristae but Chloroplasts have it in thylakoid membranes

d) Mitochondria has the co enzymes NAD and FAD as electron carriers in complexes whereas Chloroplasts have NADP

e) Mitochondria have proton gradient from the inter-membrane space to the matrix but Chloroplasts have it from the thylakoid space to the stroma

f) Mitochondria have final electron acceptor of Oxygen and H+ whereas Chloroplasts have Chlorophyll in cyclic photophosphorylation and NADPH+ in non cyclic photophosphorylation.