Anabolism of carbohydratesIn these steps simple organic acids can be converted into monosaccharides such as glucose and then used to assemble polysaccharides such as starch. Glucose is made from pyruvate, lactate, glycerol, glycerate 3-phosphate and amino acids and the process is called gluconeogenesis. Gluconeogenesis converts pyruvate to glucose-6-phosphate through a series of intermediates, many of which are shared with glycolysis.
Usually fatty acids stored as adipose tissues cannot be converted to glucose through gluconeogenesis as these organisms cannot convert acetyl-CoA into pyruvate. This is the reason why when there is long term starvation, humans and other animals need to produce ketone bodies from fatty acids to replace glucose in tissues such as the brain that cannot metabolize fatty acids.
Usually fatty acids stored as adipose tissues cannot be converted to glucose through gluconeogenesis as these organisms cannot convert acetyl-CoA into pyruvate. This is the reason why when there is long term starvation, humans and other animals need to produce ketone bodies from fatty acids to replace glucose in tissues such as the brain that cannot metabolize fatty acids.
Plants and bacteria can convert fatty acids into glucose and they utilize the glyoxylate cycle, which bypasses the decarboxylation step in the citric acid cycle and allows the transformation of acetyl-CoA to oxaloacetate. From this glucose is formed.
Glycans and polysaccharides are complexes of simple sugars. These additions are made possible by glycosyltransferase from a reactive sugar-phosphate donor, such as uridine diphosphate glucose (UDP-glucose), to an acceptor hydroxyl group on the growing polysaccharide. The hydroxyl groups on the ring of the substrate can be acceptors and thus polysaccharides produced can have straight or branched structures. These polysaccharides so formed may be transferred to lipids and proteins by enzymes called oligosaccharyltransferases.