Nutrient Digestion and Absorption of Carbohydrates and Proteins

Question 1

List the principle dietary constituents.

Answer 1

• carbohydrates
• proteins
• fats
• vitamins
• minerals
• water

Question 2

True or False.

The body can absorb disaccharides.

Answer 2

False.

The body can only absorb monosaccharides.

Question 3

Name three monosaccharides.

Answer 3

• glucose
• fructose
• galactose

Question 4

How are disaccharides absorbed?

Answer 4

• brush border enzymes break down the glycosidic bonds

Question 5

What will happen if disaccharides are not broken down?

Answer 5

• they will affect the osmotic relationship
• This will make water move into the lumen
• thus causing diarrhoea

Question 6

What are the break-down products of lactose and which enzyme catalyses the reaction?

Answer 6

• glucose and galactose

- catalysed by lactase

Question 7

What are the break-down products of sucrose and which enzyme catalyses the reaction?

Answer 7

• glucose and fructose

- catalysed by sucrase

Question 8

What are the break-down products of maltose and which enzymes catalyses the reaction?

Answer 8

• glucose and glucose

- catalysed by maltase

Question 9

Name three polysaccharides.

Answer 9

• Starch
• Cellulose
• Glycogen

Question 10

What is starch composed of?

Answer 10

• glucose monomers linked by alpha-1,4-glycosidic bonds

Question 11

What is cellulose composed of?

Answer 11

• glucose monomers linked by beta-1,4-glycosidic bonds

Question 12

What is glycogen composed of?

Answer 12

• glucose monomers linked by alpha-1,4-glycosidic bonds

Question 13

What lines the lumen of the intestines?

Answer 13

• villi, each containing microvilli

Question 14

What separates the epical membranes of the villi and the basolateral membranes of the microvilli?

Answer 14

• a tight junctional complex

- attachment proteins

Question 15

How many transport proteins would a polar molecule need to pass from the lumen into the bloodstream?

Answer 15

• A minimum of two

Question 16

Describe the absorption of glucose.

Answer 16

• glucose accumulates until the blood glucose concentration exceeds 5mmol/L
• passes through the sodium-coupled glucose transporter 1 (SGLT1)
• then is transported through the basolateral membrane by GLUT-2

Question 17

What two carbohydrates pass through the SGLT1 transporter?

Answer 17

• glucose

- galactose

Question 18

Describe how fructose is absorbed.

Answer 18

• via the GLUT-5 transporter in the epical membrane

- via the GLUT-2 transporter in the basolateral membrane

Question 19

What is the action of enzymes on proteins for digestion?

Answer 19

They hydrolyse the peptide bonds and reduce proteins to amino acids.

Question 20

Name the two types of peptidase.

Answer 20

• endopeptidase

- exopeptidase

Question 21

Explain the difference between endopeptidase and exopeptidase.

Answer 21

Endopeptidase - hydrolyses the peptide bonds in the middle of the chain
Exopeptidase - can only hydrolyse the terminal groups of the chain

Question 22

Describe the absorption of amino acids.

Answer 22

• they are transported through the sodium amino acid transporter (SAAT1) at the epical membrane
• the amino acids then must travel through another transporter on the basolateral membrane

Question 23

True or False.

70% of protein uptake is in amino acid form.

Answer 23

False.

70% of protein uptake is in dipeptide or tripeptide form.

Question 24

Describe the absorption of dipeptides.

Answer 24

• the peptide must couple with hydrogen
• travels through the PepT1 transporter
• the peptide travels through an unknown transporter in the basolateral membrane

Question 25

What happens to the hydrogen absorbed during the absorption of dipeptides?

Answer 25

• the hydrogen is transported out via NHE3 transporter
• it is released into the acid microclimate which exists around the microvilli
• the low pH attracts the hydrogen to keep it near the microvilli