Nutrient Digestion and Absorption Flashcards
What are the hexose sugars?
glucose, galactose, fructose
Where are the enzymes found that break disaccharides down into constituent monomers?
Brush border enzymes in the small intestine
What is the function of lactase, sucrase and maltase
What are the two common forms of starch?
Alpha amylose (straight chains)
Amylopectin (highly branched)
How is starch broken down?
•Glucose monomers linked by a-1,4 glycosidic bonds - hydrolysed by amylases (saliva, pancreas)
What is the structure of cellulose?
constituent of plant cell walls
- Unbranched, linear chains of glucose monomers linked by b-1,4 glycosidic bonds
- Dietary fibre (no enzymatic digestion in vertebrates - require bacteria (cellulase))
What is the function of glycogen?
animal storage form of glucose
Glucose monomers linked by a-1,4 glycosidic bond
Why can’t animals digest cellulose?
Don’t express cellulase
When does fat produciton start?
After glycogen storage is full
What is the effect of maltase?
Breaks maltose into two glucose monomers
Where are microvilli found?
There exists microvilli on the columnar epithelium of the villi
What is the function of the apical membrane?
Where the molecules enter the villi
What is the name given to the inferior surface of the villi?
Basolateral membrane
What is the difference between transcellular and paracellular transport?
Transcellular is straight through the cell
Paracellular travels throught the tight junction between the cells
How does the SGLT1 transporter work?
Sodium coupled glucose transporter – two binding sites, one for sodium and one for glucose. When they bind they are both flipped into the cell. Glucose builds up until it exceeds blood glucose. Blood concentration is 5 milimoles per litre. Because sodium is pumped out of the basal side, there is now an attraction for water through the tight membrane. SGLT1 also recognises galactose but not fructose
What is the name of the glucose transporter on the basolateral side of the villi?
GLUT - 2
Why isn’t there a blood concentration of fructose?
Fructose gets metabolised by the body, therefore no need for a sodium couple
What are the names of the fructose transporters on either side of the villi?
Glut-5 and Glut 2
What are peptides?
•Small proteins, 3-10 amino acids in length = peptides
What is the name given to the bond between the amino group and the carboxyl group?
Peptide bond
What is the name given to the enzymes which hydrolyse peptide bonds and reduce proteins or peptides to amino acids?
proteases or peptidases
What is the difference between endopeptidases and exopeptidases?
Endopeptidases act on the peptide bond in the middle of a peptide
Exopeptidase acts on the ends of the protein, depending on the end will determine which enzyme it is referred to (amino or carboxy)
How is an amino acid transported across the membrane?
The transporter is called SAAT1, and the mechanism is the same as glucose absorption
What form does the vast majority of absorbed protein take?
Di and tripeptides
What is the name given to the transporter responsible for the transport of di and tripeptides?
PepT1
What is the PepT1 transport protein linked with?
Hydrogen
How is the hydrogen trapped?
By the mucous in the membrane, creating an acid microclimate
If the PepT1 is responsible for bringing hydrogen into the cell, what is responsible for removing the hydrogen?
NHE3 sodium pump, expels the hydrogen into the acid microclimate
What expels sodium from the cell?
Sodium potassium pump
Do di and tripeptides have to be broken down when passing through the cell?
They can pass through unchanged, for example penicillin is a tripeptide. Cephalosporin antibiotics such as penicillin are all tripeptides
