A population of bacteria is breaking down some lipids to support microbial growth. Where do the products of lipid breakdown enter the central metabolic pathway?
The correct answer and explanation is:
The products of lipid breakdown enter the central metabolic pathway at the level of acetyl-CoA.
Lipid molecules, such as triglycerides, are broken down into their component parts—fatty acids and glycerol. The glycerol undergoes glycolysis, where it is converted into dihydroxyacetone phosphate (DHAP), which is then further processed into an intermediate of the central metabolic pathway, specifically entering the glycolytic pathway.
The fatty acids are broken down through a process known as beta-oxidation. During beta-oxidation, fatty acids are converted into acetyl-CoA units, which can then enter the citric acid cycle (also called the Krebs cycle or TCA cycle). Acetyl-CoA is a key molecule in cellular metabolism and serves as a central entry point for various metabolic processes.
Once inside the citric acid cycle, acetyl-CoA is combined with oxaloacetate to form citrate. Through a series of enzymatic reactions, citrate is converted back into oxaloacetate, releasing energy in the form of ATP, NADH, and FADH2, which are used by the cell for various functions, including energy production and biosynthesis.
Thus, the breakdown products of lipids—acetyl-CoA from fatty acids and intermediates from glycerol—are integrated into the central metabolic pathway, allowing the cell to generate energy and support growth. This is important because lipid metabolism provides a significant energy source, especially in cells that require large amounts of ATP, like muscle cells and certain microbes.