Briefly explain how the abundant dietary disaccharides maltose, lactose, and sucrose are metabolized by the glycolytic pathway.

Maltose, lactose, and sucrose are disaccharides, which means they are composed of two monosaccharide units. These monosaccharides are glucose, which is the main player in the glycolytic pathway. The three disaccharides are composed as follows: - Maltose: Glucose + Glucose - Lactose: Glucose + Galactose - Sucrose: Glucose + Fructose

Each disaccharide is first broken down into its respective monosaccharides before entering the glycolytic pathway: - Maltose is broken down by the enzyme maltase into two glucose molecules. - Lactose is broken down by the enzyme lactase into one glucose and one galactose molecule. - Sucrose is broken down by the enzyme sucrase into one glucose and one fructose molecule.

Now that the disaccharides have been broken down into their monosaccharide components, they can enter the glycolytic pathway. - Glucose, derived from all three disaccharides, enters the glycolytic pathway directly by being phosphorylated by hexokinase to glucose-6-phosphate. - Galactose (from lactose digestion) is first converted to glucose-6-phosphate by a series of enzymatic reactions involving galactokinase, galactose-1-phosphate uridylyltransferase, and phosphoglucomutase. - Fructose (from sucrose digestion) is metabolized via the fructose-6-phosphate pathway. Fructose is phosphorylated by fructokinase to fructose-1-phosphate, which is then cleaved into glyceraldehyde and dihydroxyacetone phosphate by aldolase B. Finally, glyceraldehyde is further phosphorylated by triose kinase to form glyceraldehyde-3-phosphate, which can enter the glycolytic pathway. In conclusion, maltose, lactose, and sucrose can be metabolized in the glycolytic pathway by breaking them down into their respective monosaccharide units and converting these monosaccharides into intermediates that enter glycolysis, ultimately producing ATP as an energy source.