tailieunhanh - Ebook Elsevier's integrated review biochemistry (2nd edition): Part 2

(BQ) Part 2 book "Elsevier's integrated review biochemistry" presents the following contents: Metabolism of steroids and other lipids, amino acid and heme metabolism; integration of carbohydrate, fat and amino acid metabolism; purine, pyrimidine, and single carbon metabolism; organization, synthesis and repair of DNA,. | Metabolism of Steroids and Other Lipids 11 CONTENTS STEROID METABOLISM Cholesterol Synthesis Bile Acids PHOSPHOGLYCERIDE METABOLISM Synthesis of Simple Phosphoglycerides Complex Phospholipids Phospholipases respiRatOry distress syndrome SPHINGOLIPID METABOLISM Ceramide Synthesis ABO Blood Groups Sphingolipidoses Lipid Storage Diseases EICOSANOIDS Prostaglandins Thromboxanes Leukotrienes Cholesterol Synthesis Cholesterol is synthesized in four phases all of which are in the cytoplasm. First the precursor mevalonate is synthesized followed by its conversion to an isoprenoid 5 Carbons intermediate. Then the isoprenoid intermediate is polymerized into a 30-carbon steroid carbon skeleton squalene. The final phase consists of cyclizing and refining the 30-carbon squalene to produce the 27-carbon cholesterol. Nicotinamide adenine dinucleotide phosphate NADPH is a coenzyme for many of the reductive biosynthesis steps in this pathway. Six-Carbon Mevalonate Three reactions synthesize 6-carbon mevalonate by condensation of 3 molecules of acetyl-CoA Fig. 11-2 . STEROID METABOLISM Cholesterol is the most ubiquitous and abundant steroid found in human tissue. It serves as a nucleus for the synthesis of all steroid hormones and bile acids. The major location for the synthesis of cholesterol is the liver although it is synthesized in significant amounts in intestinal mucosa adrenal cortex the testes and the ovaries. Cholesterol is composed of a fused ring system cyclopentanoperhydrophenanthrene CPPP with a hydroxyl group on carbon 3 and an aliphatic chain on carbon 17 Fig. 11-1 . All 27 carbon atoms of cholesterol originate from acetyl-coenzyme A CoA . The major categories of steroids are based on the side chain attached to the C17 position of the CPPP nucleus Estrogens C18 . 18-carbon steroids Androgens C19 steroids Progesterone and adrenal cortical steroids C21 steroids Bile acids C24 steroids Cholesterol and cholecalciferol not shown in Fig. 11-1 C27 steroids Thiolase Two .