Monosaccharides are reduced to their corresponding alcohols by reducing agents such as sodium amalgam or by hydrogen under high pressure in the presence of a catalyst. For example, aldoses yield the following alcohols: D-glucose D-sorbitolD-galactose D dulucitolD-mannose D-mannitol Similarly, ketoses also yield two alcohols due to the formation of a new asymmetric carbon in the C-2 position.…
Gluconeogenesis mainly occurs in the cytosol. Gluconeogenesis mostly takes place in the liver and, to some extent, in the kidney matrix;
Gluconeogenesis is the term used to include all pathways responsible for converting all non-carbohydrate precursors to glucose or glycogen. Liver and kidney are the major gluconeogenic tissues. Gluconeogenesis meets the glucose requirement of the body when carbohydrate is not available in the required amount from the diet or from glycogen reserves. Erythrocytes and nervous systems especially require…
INTRODUCTION The synthesis of glucose of glycogen from a non-carbohydrate compounds is known as gluconeogenesis. The major substrates precursors for gluconeogenesis are lactate and pyruvate, glucogenic amino acids, propionate, and glycerol.
The principal products of pentose phosphate pathway are ribose 5-phosphate and NADPH. The transaldolase and transketolase reactions convert excess ribose 5-phosphate to glycolytic intermediates when the metabolic needs for NADPH excess that of ribose 5-phosphate in nucleotide biosynthesis. The resulting gap and fructose 6-phosphate can be consumed through glycolysis and oxidative phosphorylation by gluconeogenesis. Flux…
NADPH is needed for the reductive biosynthesis of fatty acids and steroids, and therefore, HMP occurs more actively in the tissues concerned with lipogenesis, for example, adipose tissue and liver. NADPH is used in the synthesis of amino acids involving the enzyme glutamate dehydrogenase. There is a continuous production of H2O2 in living cells, which is…
In the HMP shunt, hexoses are converted into pentoses, the most important being ribose 5-phosphate. It is useful for the synthesis of nucleic acids (RNA and DNA) and many nucleotides such as ATP, NAD+, FAD, and CoA.
Aldoses are oxidised to different compounds based upon the reactants. The following are a few examples: Glucoses produce glucuronic acid, whereas galactose and mannose yield galacturonic acid and mannuronic acid, respectively.
HMP shunt is unique in generating two important products: pentoses and NADPH needed for the biosynthetic reactions and other functions. The sequence of reactions of HMP shunt is divided into two phases as shown in Figure 8.26. Figure 8.26 Hexose Monophosphate Pathway
The non-oxidative reactions are concerned with the inter-conversion of 3−, 4−, 5−, and 7-carbon monosaccharides. Ribulose 5-phosphate is acted upon by an enzyme epimerase to produce xylulose 5-phosphate while ribose ketoisomerase converts ribulose 5-phosphate to ribose 5-phosphate. The enzyme transketolase catalyse the transfer of two carbon moiety from xylulose 5-phosphate to ribose 5-phosphate to give…