Answer to Question #188434 in Biochemistry for Raiko

Question #188434

Answer the ff. questions:


1. How much energy, in the form of ATP, is obtained from b-oxidation of 1 mol of linoleic acid?


2. What would be the metabolic consequences of cells not expressing LDL receptors?


3. Vitamin D3 is derived from cholesterol. How and in which tissues does conversion occur?

Expert's answer
  1. For 1 molecule of acid - 148 ATP molecules. In 1 mol of acid - 6.02214076×1023 molecules. So the total output from beta-oxidation of 1 mol of linoleic acid is 888×1023 molecules of ATP.
  2. The low-density lipoprotein (LDL) receptor mediates the endocytosis of cholesterol-rich LDL. The loss of function is involved in the development of atherosclerosis, which is the process responsible for the majority of cardiovascular diseases, due to accumulation of LDL-cholesterol in the blood[citation needed]. Hyperthyroidism may be associated with hypocholesterolemia via upregulation of the LDL receptor, and hypothyroidism with the converse. A vast number of studies have described the relevance of LDL receptors in the pathophysiology of atherosclerosis, metabolic syndrome, and steatohepatitis.
  3. Under the influence of ultraviolet light, 7-dehydrocholesterol (a cholesterol derivative) is converted in the skin into vitamin D3, cholecalciferol (photolysis reaction). In the course of this non-enzymatic reaction, under the influence of UV radiation, the bond between the ninth and tenth carbon atoms in the cholesterol molecule breaks, the B ring opens. In the skin, cholecalciferol binds to a specific vitamin D-binding protein (transcalciferin), enters the bloodstream and is transferred to the liver, where it is hydroxylated at the 25th carbon atom to form calcidiol. In combination with vitamin D-binding protein, calcidiol is transported to the kidneys and hydroxylated at the first carbon atom to form calcitriol, the active form of vitamin D3.

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