Question

A low level of carbon dioxide labeled with 14C is accidentally released into the atmosphere surrounding industrial workers as they resume work following the lunch hour. Unknowingly, they breathe the contaminated air for 1 hour. Which of the following compounds will be radioactively labeled?

A. The carboxyl atom of newly synthesized fatty acids.

B. About one third of the carbons of newly synthesized malonyl CoA.

C. All of the carbon atoms of newly synthesized fatty acid.

D. About one half of the carbon atoms of newly synthesized fatty acids.

E. One half of the carbon atoms of newly synthesized acetyl CoA.

Answer 1

The reaction where the addition of carbon dioxide takes place in the formation of malonyl Co. A from acetyl Co.A by the enzyme acetyl.Co.A carboxylase. this is the committing step of fatty acid synthesis. However, this added carbon dioxide is removed later and the resulting fatty acids would not have the radiolabelled carbon. the source of the carbon dioxide is the dissolved bicarbonate and the formation of this bicarbonate from inhaled Co2 is very less. so only about one-third of the newly synthesized malonyl Co. A would have the radiolabelled carbon.

the CO2 addition and removal are shown in green