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DIGESTION AND METABOLISM OF CARBOHYDRATE (DIGESTION (DISACCHARIDE (Types…
DIGESTION AND METABOLISM OF CARBOHYDRATE
DIGESTION
DISACCHARIDE
Types
Maltase
Lactase
Sucrase-isomaltase (bifunctional enzyme catalyzing hydrolysis of sucrose and isomaltose)
Reaction catalyzed
Sucrose Isomaltose :arrow_right: 3 Glucose + Fructose
Lactose :arrow_right: Glucose + Galactose
Maltose :arrow_right: Glucose + Glucose
Present in the bush border epithelium of intestinal mucosal cells
FINAL HYDOLYSIS - LUMINAL SURFACE OF SMALL INTESTINE EPITHELIAL CELLS
Exoenzyme
Cleave one unit glu at a time
Alpha- glucosidase
Beta- glucosidase
IN SMALL INTESTINE
Main digestion take place in small intestine by pancreatic amylase
Digestion completed by pancreatic amylase (food stay longer in intestine)
In duodenum
Food bolus meets pancreatic juice
Pancreatic juice contain pancreatic amylase @ amylopsin (carbohydrate splitting enzyme- similar to salivary amylase)
food bolus reach duodenum fom stomach
Action of pancreatic amylase
Optimum pH: 7.1
An isoenzyme of salivary amylase but differ in optimum pH of action
Type of amylase: alpha- amylase
Require Cl- ion for its activity
Hydrolyse alpha-1,4 glycosidic linkage of polysaccharide molecule
Reaction catalyzed
Starch :arrow_right: Maltose/ Isomaltose + Dextrin and oligosaccharides
Pancreatic amylase product
Trisaccharide maltotriose
Alpha-limit dextrin (~glucose unit with 1 or more 1,6-glycosidic bond)
Disaccharide maltose
IN STOMACH
Action
No enzyme for glucosidic bond linkage
Hydrochloride (HCl) can hydrolyse sucrose form glucose and fructose
OTHER UNHYDROLYSED CANNOT BE ABSORBED
Enter lower tract of intestine
Used by bacteria resulting in producing of
Hydrogen gas
Methane
CO2
IN MOUTH
Action of Ptylin (Salivary amylase)
Incomplete process
Location: mouth
Shorter duration
Action
Require Cl- ion for activation of optimum pH of 6.7 (range 6.6 to 6.8)
Alpha-amylase hydrolyse alpha-1,4 glycosidic linkage in polysaccharide molecule
Type of amylase: alpha- amylase
Ptylin action stop at stomach (pH falls to 3.0)
clinical significance (digestion)
congenital lactose intolerance
deficiency of lactase enzyme
develops immediately after birth
milk feed precipitates symptoms
primary lactase deficiency
develops over time
intolerance to milk and dairy products
secondary lactase defiency
develop in a healthy person during episodes of acute illness
ABSORPTION
monosaccharides
absorption of monosaccharides
enzymes on the luminal surface of the small intestine epithelial cells digest disaccharides into monosaccharides
monosaccharides are absorbed into the cells by facilitated diffusion by secondary active transport with Na+
the absorbed monosaccharides enter the blood. the bloodstream distributes the nutrients throughout the body
factors affecting rate of absorption
he absorption is faster through intact mucosa and slower if there is some injury to the mucosa
the rate of absorption of glucose increase by thyroid hormone
mineralorcoticoid increase the rate of absorption
glucose and galactose
absorbed via secondary active transport by a symporter
glucose transporters
Na+ dependent (SGLT)
type of co-transporter
2 binding sites : for Na+ and for glucose
after Na+ binding, conformational occurs to make sure glucose can bind
Na+ is transported across membrane where down concentration gradient and glucose against the concentration gradient
Na+ independent (GLUT)
used for facilitated transport
numbered from 1 to 14 GLUT
fructose
facilitated transport
the absorption is slower than glucose and galactose abosrtion
sugars absorbed by enterocytes
mechanisms
passive diffusion
facilitated diffusion
uptake of glucose in peripheral cells
facilitated diffusion
numbered from 1 to 7 (GLUT 1 to GLUT 7)
active transport
clinical significance (absorption)
in deficency of SGLT - 1, glucose unabsorbed and excreted in feces
in deficiency of SGLT - 2, the filtered glucose is not absorbed back then lost in urine which cause glycosuria
METABOLISM
Catabolic proses
Glycolysis
breakdown of glucose to pyruvic acid
occurs in the cytoplasm
net gain 2 ATP, 2 NADH and 2 molecules of pyruvic acid
Citric acid cycle
occurs in the mitochondria
produces CO2, GTP, 3 NADH and 1 FADH2
Glycogenolysis
Breakdown of glycogen to glucose
Hexose monophosphate pathway
alternative pathway for glucose oxidation which neither utilizes nor produces ATP
Uronic acid pathway
synthetic pathway for the various uronic acids
anabolic proses
Glycogenesis
Synthesis of glycogen from glucose
Gluconeogenesis
formation of glucose from non-carbohydrate sources
by:
Nuhilhadiah Binti Suatman (70832)
Nur Anesa Binti Mohd Sedek (70870)
