Question

You have been studying hard for the last few days and you have completely forgotten to eat since yesterday morning. Explain how your short fast affects lipid metabolism in your body and make sure to include ALL relevant enzymes and describe how they are regulated.

Answer 1

Our body gets energy from the food we eat. The food is broken down into it's simplest form like carbohydrates, lipids, proteins, vitamins etc so thet the cells can absorb these nutrients and carry out it's functions. Glucose is the main source of energy which we get from food. When we don't eat for almost 24 hrs and more, our body gets deprived of glucose. When the glucose reserve finishes then our body breaks down lipids for energy. This principle is followed in intermittent fasting to cut down body fats.

When we do short fasting first of all the glycogen reserve are broken down by gycogenolysis into glucose. At this point body's blood insulin level becomes very low and our brain need a continuous supply of glucose to be active. When the body cannot produce glucose from glycogen then the fats are broken down into fatty acids and glycerol by the process of lipolysis and further the fatty acids are directly broken down to generate energy. The fatty acid is further oxidized to form acetyl CoA by beta-oxidation process. The first step in lipolysis is, the triacylglycerol is converted into a diacylglycerol by the enzyme adipose triglyceride lipase (or ATGL), this enzyme helps in hydrolyzing adipose tissue lipids. Then the diacylglycerol is converted to monoacylglycerol by the enzyme hormone-sensitive lipase (HSL), this enzyme helps to remove a glycerol group. At the end monacylglycerol is down to a glycerol molecule by the enzyme monoacylglycerol lipase (MGL). The glycerol generated enters the glycolysis pathway in the form of DHAP. The three fatty acids produced from one triglyceride is converted to fatty acyl CoA molecules in the cytoplasm then it adds with carnitine to form a fatty acyl carnitine molecule, this helps in fatty acid transportation across the mitochondrial membrane. Then inside the mitochondrial matrix the fatty acyl carnitine is converted back to fatty acyl CoA then finally to acetyl CoA and acyl CoA. The acetyl CoA then enters the kreb's cycle to generate ATP, the energy unit for cell. In this way body gets energy from lipids during short fasting.