lect 3 Flashcards
- Digestion in Mouth
• Digestion of carbohydrates starts at the mouth, where they come in
contact with saliva during mastication
• Saliva contains a carbohydrate splitting enzyme called salivary amylase (ptyalin)
Action of Ptyalin (Salivary Amylase)
It is -amylase, requires Cl- ion for activation and optimum pH 6-7
The enzyme hydrolyzes α-(1,4) glycosidic linkage at random, from molecules like starch, glycogen and dextrins, producing smaller molecules maltose, glucose and disaccharides maltotriose
Ptyalin action stops in stomach when
pH falls to 3.0
- Digestion in Stomach
- No carbohydrate splitting enzymes are available in gastric juice
- HCl may hydrolyze some dietary sucrose to equal amounts of glucose and fructose
- Digestion in Duodenum
- Food reaches the duodenum from stomach where it meets the pancreatic juice
- Pancreatic juice contains a carbohydrate-splitting enzyme pancreatic amylase
Action of Pancreatic Amylase
- It is also an -amylase, optimum pH 7.1
- Like ptyalin it also requires Cl- for activity
- The enzyme hydrolyzes -(1,4) glycosidic linkage situated well inside polysaccharide molecule
- Digestion in Small Intestine
a. Pancreatic Amylase:
b. Lactase
• It hydrolyzes terminal -(1,4), glycosidic linkage in polysaccharides and oligosaccharide
molecules liberating free glucose molecules
a. Pancreatic Amylase:
- It is a β- glycosidase, its pH range is 5.4 to 6.0
- Lactose is hydrolyzed to glucose and galactose
- Trehalase degrades trehalose to glucose
- Sucrase degrades sucrose to glucose and fructose
b. Lactase
• Lactose is hydrolyzed to galactose and glucose by lactase in humans (by β- Galactosidase in
Bacteria)
- Some adults do not have lactase
- Such adults cannot digest the sugar
- It remains in the intestines and gets fermented by the bacteria
- The condition is called as Lactose intolerance
- Such patients suffer from watery diarrhea, abnormal intestinal flow and choleric pain
- They are advised to avoid the consumption of lactose containing foods like milk
Lactose Intolerance
• The enzyme hydrolyzes the α -(1,4) glycosidic linkage between
glucose units in maltose molecule liberating two glucose molecules
• Its pH range is 5.8 to 6.2
c. Maltase
- pH ranges 5.0 to 7.0
* It hydrolyzes sucrose molecule to form glucose and fructose
d. Sucrase
no atp required
no energy required
passive
requires energy in the form of atp
active
from high to low concentration
passive
