Carbohydrates Flashcards
What is the major dietary polysaccharide?
starch
What do human cells synthesize to digest polysaccharides?
α-endoglycosidases
Why can’t humans digest celulose?
we do not synthesize β-endoglucosidases
Where does digestion of α-dextrins and disaccharides occur?
in small intestine
Why is α-amylase is largely inactivated in the stomach?
due to the acidity, so it becomes denatured and digestion stops for a moment
After the action of pancreatic α-amylase, _____ (fragments of poylsaccharides) are processed into disaccharide, trisachardies and oligosaccharides
α-dextrins
Is Maltose a reducing sugar?
Yes
Is Sucrose a reducing sugar?
No
Is Lactose a reducing sugar?
yes
What are the 2 components of starch?
amylose α-(1→4) links
amylopectin α-(1→6)
Lactose and Sucrose can’t be broken down in the stomach because they have what bonds?
β(1-4) and α(1,2) respectively
What is the difference between maltose and isomaltose?
isomaltose is 2 glucose with a (1,6) link
Is there carbohydrate digestion in the stomach?
no
what causes lactose intolerance?
a defect in specific disaccharidases in intestinal mucosa so that undigested carbohydrates enter the large intestine
what demographic is lactose intolerance mostly seen in?
African and Asians ~90%
how are glucose and galactose transported into the mucosal cell?
secondary active carrier mediated sodium dependent glucose transporter-1 (SGLT-1)
how are fructose along with glucose and galactose transported into the cell?
sodium-independent monosaccharide transporter (GLUT5); this is a facilitated transporter (GLUT5)
describe the exit of the 3 monosaccharides
they exit the mucosal cell and enter into portal circulation via GLUT-2
Which GLUT transporters have a high affinity for glucose?
GLUT 1, GLUT 3
Which GLUT transporter has a low affinity for glucose?
GLUT 2
What is the km of GLUT 1?
1mM
What is the km of GLUT 2?
15mM
What is the km of GLUT 3?
1mM
What is the km of GLUT 4?
5mM
Where is GLUT 1 found?
human erythrocyte, all the blood-brain etc barriers
Where is GLUT 2 found?
liver, kidney, pancreatic B cell
Where is GLUT 3 found?
brain
Where is GLUT 4 found?
adipose tissue, skeletal muscle, heart muscle
Where is GLUT 5 found?
intestinal epithelium, spermatoxia
What is different about GLUT 4 and 5?
GLUT 4-insulin-sensitive transporter
GLUT 5- fructose transporter
What bonds does Maltose have?
α-(1→4)
What bonds does Sucrose have?
α-(1→2)
What bonds does Lactose have?
β-(1→4)
What bond does amylopectin have?
α-(1→6)
What do salivary and pancreatic α-amylase have activity towards?
only those linked by α-(1→4) bonds
where does the final digestion occur?
mucosal lining of the upper jejunum
what gases lead to flatuance?
methane, carbon dioxide, hydrogen
