Digestion of Carbs and Proteins Flashcards
What breaks down disaccharides in the small intestine?
Brush border enzymes on the surface
3 main polysaccharides
Starch
Glycogen
Cellulose
Two types of starch
a-amylose
amylopectin
Structure of amylose
straight chains of glucose
Structure of amylopectin
Highly branched chains
What are the bonds found in cellulose
beta-1,4 glycosidic bonds
Why does lactose intolerance cause its symptoms?
Unabsorbed lactose causes an osmotic gradient in the lumen, pulling water into it
What is glucose-galactose absorption syndrome?
Lack of expression of transport proteins, meaning those sugars cannot be absorbed
What membrane contains the microvilli of the small intestine?
Apical membrane
Transcellular transport requires how many transport proteins? Do they work both ways?
2
1 for in
1 for out
Unidirectional
What pathway occurs around cells?
Paracellular pathway
What is the biosynthetic pathway?
Production of proteins inside the cell to then be transported out (RER -> Golgi -> out)
What is vectorial transport?
Transport of molecules in or out the cell, which can only occur in one direction
What is the basolateral membrane?
The underside/outside of small intestine cells
How is glucose transported INTO intestinal cells?
Coupled with Sodium for SGLT1
What is SGLT1
Sodium coupled glucose transport enzyme
How is glucose passed from the cell to the blood?
GLUT-2 transport protein
What does SGLT1 transport?
Glucose AND galactose coupled with Na
How is an inward sodium gradient maintained in intestinal cells?
Na-K ATPase
Why does H20 readily follow glucose into the blood?
Large inflow of Na into the blood causes an osmotic gradient to form
Water easily passes through tight junction
How does fructose pass from lumen to the cell?
GLUT-5 protein
Why doesnt fructose require a transporter?
We don’t have a blood fructose level, so fructose always flows in
Why does water not follow fructose into the blood stream?
No Na transported with the fructose so no concentration gradient is formed
What does GLUT-5 transport?
Fructose (out of cell)
What does GLUT-2 transport?
Fructose, glucose and galactose (out of cell)
What do proteases do?
Hydrolyse peptide bonds (break down proteins to amino acids)
What is the function of endopeptidases?
Break peptide bonds in the middle of proteins
What are exopeptidases?
Break amino acids off the ends of proteins
What is an aminopeptidase?
An exopeptidase which breaks an AA off the amino end
What is a carboxypeptidase?
An exopeptidase which breaks an AA off the carboxy end
How are single amino acids transported from the lumen to the cell?
Sodium coupled amino acid transporter
How are 70% of amino acids taken up?
Di-/tripeptides
How are tri-/dipeptides taken from the lumen to the cell?
PepT1
Protein coupled transport protein
How is the acidic microclimate of the lumen maintained?
NHE3
Pumping of protons out of the cell back into the lumen in exchange for a Na
