3.3.3 Digestion and absorption

Question 1

what is digestion?

Answer 1

large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes

Question 2

which enzymes hydrolyse carbohydrates into monosaccharides?

Answer 2

• amylase
• membrane-bound disaccharidase

Question 3

how are the salivary glands involved in the digestion of carbohydrates?

Answer 3

• produce amylase in saliva
• hydrolyses glycosidic bonds in starch to form maltose

Question 4

how is the pancreas involved in the digestion of carbohydrates?

Answer 4

• pancreatic amylase released into the small intestine
• hydrolyses glycosidic bonds in starch to form maltose

Question 5

how is the small intestine (ileum) involved in the digestion of carbohydrates?

Answer 5

• breaks glycosidic bonds to hydrolyse disaccharides into monosaccharides

Question 6

what are the three membrane-bound disaccharidases?

Answer 6

• maltase
• sucrase
• lactase

Question 7

which three proteases hydrolyse larger protein molecules?

Answer 7

• endopeptidases
• exopeptidases
• membrane-bound dipeptidases

Question 8

what is the role of an endopeptidase?

Answer 8

hydrolyses internal peptide bonds (bonds between amino acids in the middle of a polymer chain)

Question 9

what is the role of an exopeptidase?

Answer 9

hydrolyses terminal peptide bonds (bonds between amino acids at the end of a polymer chain)

Question 10

what is the role of a membrane-bound dipeptidase?

Answer 10

hydrolyses peptide bonds between two amino acids (a dipeptide)

Question 11

how are lipids digested?

Answer 11

• lipase produced in the pancreas hydrolyses the ester bonds in triglycerides to form the monoglycerides and fatty acids
• bile salts are produced in the liver which emulsify lipids to form tiny droplets called micelles
• this increases the SA for lipase to act on

Question 12

how are monosaccharides and amino acids digested?

Answer 12

• to absorb glucose and amino acids from the lumen to the gut there must be a higher concentration in the lumen compared to the epithelial cell
• therefore, active transport and co-transport are required

Question 13

what are micelles?

Answer 13

water-soluble vesicles formed of fatty acids, monoglycerides and bile salts

Question 14

how are lipids absorbed?

Answer 14

• micelles encounter ileum epithelial cells
• as fatty acids and monoglycerides are non-polar, they diffuse simply across the cell membrane to enter epithelial cells
• once in the cell, they are modified back into triglycerides inside the ER and Golgi body
• inside the Golgi body, they bind with cholesterol and proteins to form chylomicrons
• chylomicrons travel in a vesicle and leave the epithelial cell by exocytosis
• chylomicrons enter lymphatic capillaries called lacteals which transport them away