Nutrient digestion carbs & proteins Flashcards
What are the principal dietary constituents?
Carbohydrate Protein Fat Vitamins Minerals Water
What are monosaccharides?
Hexose sugars (6C):
Glucose
Galactose
Fructose
What are disaccharides?
Two monosaccharides linked together by glycosidic bond:
Maltose
Lactose
Sucrose
How are disaccharides broken down?
They are broken down to constituent monomers by brush border enzymes in small intestine
What is maltose, lactose and sucrose composed of?
Maltose = glucose + glucose
Lactose = glucose + galactose
Sucrose = glucose + fructose
Examples of different polysaccharides
Starch
Cellulose
Glycogen
What is Starch?
Plant storage form of glucose
alpha-amylose: glucose linked in straight chains
amylopectin: glucose chains highly branched
What is Cellulose?
Constituent of plant cell walls
- Unbranched, linear chains of glucose monomers linked by beta-1, 4 glycosidic bonds
What is Glycogen?
Animal storage form of glucose
- Glucose monomers linked by a-1,4 glycosidic bonds
How are glucose monomers linked?
They are linked by a-1, 4 glycosidic bonds
What does Amylase do?
Breaks down Starch, glycogen (glucose polymers) into Maltose
What is alpha-amylase?
Alpha-amylase, (α-amylase) is an enzyme that hydrolyses alpha bonds of large, alpha-linked polysaccharides, such as starch and glycogen, yielding glucose and maltose.
It is the major form of amylase found in humans and other mammals.
What are proteins?
Polymers of amino acids linked together by peptide bonds
What are proteases/peptidases?
Enzymes which hydrolyse peptide bonds and reduce proteins or peptides to amino acids
What is the basolateral membrane?
Basolateral membrane or serosal membrane refers to the cell membrane which is oriented away from the lumen of the tubule
What is the apical membrane?
It is the layer of plasma membrane on the apical side (the side toward the lumen) of the epithelial cells in a body tube or cavity, separated from the basolateral membrane by the zonula occludens.
What does the SGLT1 (sodium glucose linked transporter) do?
It is a glucose transporter found in the intestinal mucosa (enterocytes) of the small intestine.
- It is the main uptake mechanism for glucose and galactose in the gut.
What is the function of GLUT2?
It is a facilitative glucose transporter in the liver, pancreas, intestine and brain.
- Apical GLUT2 also increases fructose uptake.
What is the fructose transporter in the small intestine?
GLUT5
It is expressed on the apical border of enterocytes in the small intestine.
Where do endopeptidases work?
In the interior of the protein
Where do exopeptidases work?
They only act on the terminal amino acid
How are small peptides absorbed into the small intestinal epithelial cell ?
By cotransport with H+ ions via a transporter called PepT1
What is NHE3 (sodium-hydrogen antiporter 3)?
It is a protein that in humans is encoded by the SLC9A3 gene
- It is primarily responsible for maintaining the balance of sodium.
