GI Questions 2 - Nutrient Digestion and Absorption

Question 1

What is the only form the body can absorb carbohydrates in, and which carbohydrates fall under this category?

Answer 1

Hexose sugars - glucose, galactose and fructose

Question 2

What are the three disaccharides made up of and what links them?

Answer 2

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

Question 3

Where are the enzymes which break down disaccharides?

Answer 3

Brush border enzymes in the small intestine

Question 4

Which polysaccharide cannot be enzymatically digested by vertebrates, and how do they digest it?

Answer 4

Cellulose - cellulase production by bacteria

Question 5

What form do plants store glucose in, what type of bond links the glucose monomers, and which enzyme is required to break them down?

Answer 5

Starch, α-1,4-glycosidic bonds, amylases in the saliva and the pancreas

Question 6

What form do animals store glucose in, what type of bond links the glucose monomers, and which enzyme is required to break them down?

Answer 6

Glycogen, α-1,4-glycosidic bonds, amylases in the saliva and the pancreas

Question 7

What form does α-amylose take?

Answer 7

Polysaccharide of glucose units bound linearly by α-1,4-glycosidic bonds - 30% of starch

Question 8

What form does amylopectin take?

Answer 8

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

Question 9

What separates the apical membrane of columnar cells from the basolateral membrane?

Answer 9

Tight junctions

Question 10

What is a normal blood glucose level?

Answer 10

4.2-6.3mM - 5mM average

Question 11

Which transporter allows glucose to cross the apical membrane?

Answer 11

SGLT1 - sodium coupled glucose transporter 1

Question 12

Which transporter allows glucose to cross the basolateral membrane?

Answer 12

GLUT-2

Question 13

Which transporter allows fructose to cross the apical membrane?

Answer 13

GLUT-5

Question 14

Which transporter allows fructose to cross the basolateral membrane?

Answer 14

GLUT-2

Question 15

What are proteins structurally made of?

Answer 15

Polymers of amino acids linked together by peptide bonds

Question 16

What are small proteins of 3-10 amino acids in length known as?

Answer 16

Peptides

Question 17

Which enzymes are required to hydrolyse proteins?

Answer 17

Proteases or peptidases

Question 18

How do endopeptidases act?

Answer 18

Endopeptidases break peptide bonds of nonterminal amino acids. Endopeptidases cannot break down peptides into monomers.

Question 19

How do exopeptidases act?

Answer 19

Exopeptidases break peptide bonds from end-pieces of terminal amino acids. Exopeptidases can break down peptides into monomers.

Question 20

Which transporter allows amino acids to cross the apical membrane?

Answer 20

SAAT1 - sodium coupled amino acid transporter 1

Question 21

What causes the acidic microclimate close to the apical membrane, and why is this beneficial?

Answer 21

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.