Question

How much carbon dioxide is produced from the complete aerobic catabolism of one molecule of linoleate via catabolic pathways?

A) 18 CO2

B) 17 CO2

C) 16 CO2

D) 15 CO2

E) 8 CO2

Answer 1

Linolenic acid, an unsaturated fatty acid with two cis double bonds, undergoes three cycles of ?-oxidation. Three molecules of acetyl CoA and a 12 carbon chain fatty acyl-CoA cis-?3,cis-?6 are formed. The ?3,?2-enoyl-CoA isomerase converts fatty acyl-CoA cis-?3,cis-?6 to trans-?2,cis-?6 fatty acyl-CoA. . This product undergoes one more cycle of ?-oxidation resulting in a fourth molecule of acetyl CoA and cis-?4 fatty acyl-CoA. The acyl-CoA dehydrogenase converts it to trans-?2,cis-?4 fatty acyl-CoA in first step of beta oxidation. The enzyme 2,4-dienoyl CoA-reductase converts trans-?2,cis-?4 fatty acyl-CoA to trans-?3 fatty acyl-CoA. This product is acted upon by enoyl-CoA isomerase to form trans-?2 fatty acyl-CoA.

The trans-?2 fatty acyl CoA undergoes four cycles of ?-oxidation thereby forming five molecules of acetyl CoA. Thus, total 3+1+4=9 acetyl CoA is formed from one molecule of linoleate, which enters the Kreb’s cycle. There is formation of 6 FADH2 and 8 NADH as well.

Two carbon dioxide molecules are formed form each molecule of acetyl CoA. There are two carbons present in one acetyl CoA. Each carbon will release one CO2.

Hence, total CO2 released = 9*2= 18

Right choice is A) 18 CO2