GI Questions 2 - Nutrient Digestion and Absorption Flashcards
What is the only form the body can absorb carbohydrates in, and which carbohydrates fall under this category?
Hexose sugars - glucose, galactose and fructose
What are the three disaccharides made up of and what links them?
Lactose - glucose + galactose (broken down by lactase)
Maltose - glucose + glucose (broken down by maltase)
Sucrose - glucose + fructose (broken down by sucrase)
Linked by glycosidic bonds
Where are the enzymes which break down disaccharides?
Brush border enzymes in the small intestine
Which polysaccharide cannot be enzymatically digested by vertebrates, and how do they digest it?
Cellulose - cellulase production by bacteria
What form do plants store glucose in, what type of bond links the glucose monomers, and which enzyme is required to break them down?
Starch, α-1,4-glycosidic bonds, amylases in the saliva and the pancreas
What form do animals store glucose in, what type of bond links the glucose monomers, and which enzyme is required to break them down?
Glycogen, α-1,4-glycosidic bonds, amylases in the saliva and the pancreas
What form does α-amylose take?
Polysaccharide of glucose units bound linearly by α-1,4-glycosidic bonds - 30% of starch
What form does amylopectin take?
Highly branched polysaccharide of glucose units bound linearly by α-1,4-glycosidic bonds and branching with α-1,6-glycosidic bonds - 70% of starch
What separates the apical membrane of columnar cells from the basolateral membrane?
Tight junctions
What is a normal blood glucose level?
4.2-6.3mM - 5mM average
Which transporter allows glucose to cross the apical membrane?
SGLT1 - sodium coupled glucose transporter 1
Which transporter allows glucose to cross the basolateral membrane?
GLUT-2
Which transporter allows fructose to cross the apical membrane?
GLUT-5
Which transporter allows fructose to cross the basolateral membrane?
GLUT-2
What are proteins structurally made of?
Polymers of amino acids linked together by peptide bonds
What are small proteins of 3-10 amino acids in length known as?
Peptides
Which enzymes are required to hydrolyse proteins?
Proteases or peptidases
How do endopeptidases act?
Endopeptidases break peptide bonds of nonterminal amino acids. Endopeptidases cannot break down peptides into monomers.
How do exopeptidases act?
Exopeptidases break peptide bonds from end-pieces of terminal amino acids. Exopeptidases can break down peptides into monomers.
Which transporter allows amino acids to cross the apical membrane?
SAAT1 - sodium coupled amino acid transporter 1
What causes the acidic microclimate close to the apical membrane, and why is this beneficial?
The NHE3 (Na+/H+ Exchanger) transports H+ ions out of the cell, creating an acidic microclimate close to the apical membrane of the cell. This creates an abundance of H+ ions available to facilitate PepT1 transporting di- and tripeptides into the cell.
