Carbohydrate Digestion and Absorption Flashcards

Vocabulary flashcards covering carbohydrate digestion, brush-border enzymes, monosaccharide transporters, and metabolic pathways based on NUTR 3500/6500 lecture material.

Salivary (\alpha)-amylase

An enzyme released by salivary glands in the mouth that hydrolyzes (\alpha(1-4)) glycosidic bonds in amylose and amylopectin to form dextrins and maltose; it is inactivated by gastric acid in the stomach.

Pancreatic (\alpha)-amylase

An enzyme secreted by the pancreas into the small intestine that hydrolyzes (\alpha(1-4)) glycosidic bonds in amylose and amylopectin to produce maltose, maltotriose, and (\alpha)-limit dextrins.

Isomaltase

A brush-border enzyme (also known as (\alpha)-limit dextrinase) located on the apical membrane of enterocytes that hydrolyzes (\alpha(1-6)) glycosidic bonds in (\alpha)-limit dextrins to yield glucose.

Lactase

A brush-border enzyme ((\beta)-galactosidase) that hydrolyzes the (\beta(1-4)) glycosidic bond in lactose ((C_{12}H_{22}O_{11})) to produce glucose ((C_6H_{12}O_6)) and galactose ((C_6H_{12}O_6)).

Sucrase

A brush-border enzyme that hydrolyzes the (\alpha(1-2)) glycosidic bond in sucrose ((C_{12}H_{22}O_{11})) to produce glucose ((C_6H_{12}O_6)) and fructose ((C_6H_{12}O_6)).

SGLT1

Sodium-Glucose Co-Transporter 1; an energy-dependent active transport protein on the brush border membrane of intestinal enterocytes that transports glucose and galactose into the cell using the (Na^+) gradient.

SGLT2

Sodium-Glucose Co-Transporter 2; an active transport protein located in the proximal tubule of the kidney involved in reabsorbing glucose.

GLUT5

A membrane transport protein that facilitates the entry of fructose across the apical brush-border membrane of intestinal enterocytes via facilitated diffusion.

GLUT2

A facilitated diffusion glucose transporter located on the basolateral membrane of enterocytes that supports the exit of glucose, galactose, and fructose into hepatic portal blood, as well as apical glucose transport at high mucosal concentrations.

Leloir Pathway

The metabolic pathway through which galactose is converted into glucose 1-phosphate in the liver, utilizing galactokinase and galactose 1-phosphate uridyltransferase (GALT).

Galactose 1-phosphate Uridyltransferase (GALT)

The enzyme in the second step of the Leloir pathway that converts galactose 1-phosphate into UDP-galactose; a deficiency in this enzyme causes classic galactosemia.

UDP-galactose 4-epimerase

An enzyme that converts UDP-galactose to UDP-glucose, enabling galactose utilization in glycogen synthesis, proteoglycan synthesis, and lactose production.

Fructokinase

The enzyme that catalyzes the first step of hepatic fructose metabolism by phosphorylating fructose to fructose 1-phosphate using ATP.

Aldolase B

A hepatic enzyme that cleaves fructose 1-phosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde, allowing fructose to enter glycolysis downstream of phosphofructokinase-1 (PFK-1).

Hepatic Monosaccharide Uptake

The uptake pattern of dietary sugars by the liver: (100\%) of absorbed galactose and fructose are taken up by the liver, whereas (30\%-40\%) of glucose is taken up by the liver and (60\%-70\%) passes to muscle and adipose tissue.

Intestinal Villi

Finger-like projections in the intestinal epithelium covered with enterocytes and microvilli, containing an inner capillary network and central lacteal for absorbing monosaccharides and other nutrients.