Question

Briefly describe how protein and lipid metabolism are linked to glycolysis and the Krebs cycle, and determine the ATP yield of each.

Answer 1

Connection of Lipid and sugar metabolism-

Triglycerides—made from the bonding of glycerol and three fatty acids—are a form of long-term energy storage in animals. Animals can make most of the fatty acids they need. Triglycerides can be both made and broken down through parts of the glucose catabolism pathways that include glycolysis and Kreb cycle. Glycerol can be phosphorylated to glycerol-3-phosphate, which continues through glycolysis. Fatty acids are catabolized in a process called beta-oxidation, which takes place in the matrix of the mitochondria and converts their fatty acid chains into two-carbon units of acetyl groups. The acetyl groups are picked up by CoA to form acetyl CoA that proceeds into the citric acid cycle.

ATP production occur in mitochondria where Triacylglycerol molecule split in the glycerol molecule and three water insoluble fatty acid molecule with the help of enzyme lipase. This process stimulates the diffusion of fatty acid in the circulation. Glycerol molecule is converted into 3-phosphoglyceraldehyde, which degrades into pyruvate to form ATP through oxidative phosphorylation. The complete break-down of a single glycerol molecule generates 19 ATP under aerobic conditions.

Hence, each triacylglycerol molecule release (441 ATP from fatty acid metabolism + 19 ATP from glycerol metabolism) a total of 460 ATP productions.

Connection of protein and sugar metabolism- Amino acid can be broken into precursor for the glycolysis and Kreb cycle. Amino acid can enter the cycle through more than one pathway.

Although protein breakdown is not a preferred source for energy but amino acid can be used as source of energy in case of starvation. Protein metabolism occurs exclusively in the mitochondria. The first step includes the deamination and product of deamination is converted into pyruvate. Because the processing of amino acid result in the creation of metabolic intermediate that include pyruvate, acetyl CoA, acetoacli CoA elpha – ketoglutarate. Amino acid can serve as a source of energy production through kreb cycle.