Question

What are 2 differences between glycolysis in liver cells versus muscle cells? How are these cells affected under conditions where an individual has insulin deficiency ?

Answer 1

Ans- Difference: It occurs in liver cells, and will only phosphorylate the glucose entering the cell to form glucose-6-phosphate (G6P), when the sugar in the blood is abundant. This being the first step in the glycolytic pathway in the liver, it therefore imparts an additional layer of control of the glycolytic pathway in this organ.

It is present in low levels in the muscle. Glycolysis converts glucose to pyruvate, water and NADH, producing two molecules of ATP. Excess pyruvate is converted to lactic acid which causes muscle fatigue. Cellular respiration produces further molecules of ATP from pyruvate in the mitochondria.

The only difference is that liver cells contain an isozyme of hexokinase called glucokinase.When the glucose in the blood runs low, the L-isozome of pyruvate kinase is phosphorylated, which decreases its activity and decreases the rate of glycolysis.

Liver cells affected by insulin deficiency - Insulin stimulates the liver to store glucose in the form of glycogen. A large fraction of glucose absorbed from the small intestine is immediately taken up by hepatocytes, which convert it into the storage polymer glycogen. Insulin has several effects in liver which stimulate glycogen synthesis.

Muscle cells affected by insulin deficiency - Insulin not only lowers blood sugar levels, but promotes the growth and proliferation of cells; insufficient action of insulin has been thought to result in the suppression of growth and proliferation of muscle cells, which in turn contribute to thedecline in skeletal muscle mass.