Digestion and Absorption

Question 1

what happens during digestion?

Answer 1

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

Question 2

what are the enzymes involved in the digestion of the carbohydrates in mammals?

Answer 2

• amylase
• membrane-bound disaccharidases

Question 3

what is amylase?

Answer 3

• digestive enzyme that catalyses the breakdown of starch
• starch is a mixture of 2polysaccharides(glycogen and amylopectin) = each made form a long chain of alpha-glucose molecules

Question 4

how does amylase work?

Answer 4

• catalyses hydrolysis reactions that break glycosidic bonds in starch to produce maltose(disaccharide)

Question 5

where is amylase produced?

Answer 5

• by the salivary glands, which releases amylase into the mouth
• by the pancreas which releases amylase into the small intestine

Question 6

what are membrane-bound disaccharidases?

Answer 6

• they are enzymes attached to the cell membranes of epithelial cells lining the ileum

Question 7

what do membrane-bound disaccharidases do?

Answer 7

• break down disaccharides into monosaccharides
• involves the hydrolysis of glycosidic bonds

Question 8

what is involved in the digestion of lipids?

Answer 8

• lipase enzymes
• bile salts

Question 9

what do lipase enzymes do?

Answer 9

• catalyse the breakdown of lipids in monoglycerides and fatty acids
• involves hydrolysis of ester bonds in lipids

Question 10

where are lipases mainly made and secreted?

Answer 10

• made in pancreas
• secreted into small intestine where they act

Question 11

where are bile salts produced?

Answer 11

liver

Question 12

what is the role of bile salts?

Answer 12

• to emulsify lipids = cause lipids to form small droplets
• bile salts are not enzymes, important in lipids digestion

Question 13

why are bile salts important?

Answer 13

• several small lipid droplets have a larger surface area than a single large lipid droplet
• formation of small droplets increases the surface area of lipids that’s available for lipases to work on

Question 14

what happens after lipids are broken down by lipase?

Answer 14

• monoglycerides and fatty acids stick with the bile salts to form a micelle

Question 15

how are proteins broken down?

Answer 15

• combination of peptidases
• endopeptidase and exopeptidase

Question 16

what do the peptidases do to the protein?

Answer 16

• catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids

Question 17

what is endopeptidase?

Answer 17

hydrolyse the peptide bonds within the proteins

Question 18

what is exopeptidase?

Answer 18

hydrolyse the peptide bonds at the ends of the protein
- they remove single amino acids from the protein

Question 19

what are dipeptidases?

Answer 19

• exopeptidase that work of dipeptides
• act to separate the 2 amino acids that make up a dipeptide by hydrolysing the peptide bond between them

Question 20

where are membrane- bound dipeptidases located?

Answer 20

• cell surface membrane of epithelial cells in a small intestine

Question 21

what are micelles?

Answer 21

• help the products of lipid digestion to be absorbed

Question 22

what is the mechanism for the absorption of the products of digestion by cells lining the ileum of mammals(monosaccharides)?

Answer 22

• glucose is absorbed by active transport with sodium ions , via co-transporter protein
• galactose is absorbed in the same way using same co-transporter protein
• fructose is absorbed by facilitated diffusion through a channel and carrier protein

Question 23

what is the mechanism for the absorption of the products of digestion by cells lining the ileum of mammals(monoglycerides and fatty acids)?

Answer 23

• micelles help to move monoglycerides and fatty acids through the epithelium
• micelles constantly break up and reform , they can release monoglycerides and fatty acids, allowing them to be absorbed
• whole micelles are not taken up across epithelium
• monoglycerides and fatty acids are lipid soluble, so they can diffuse directly across the epithelial cell membrane

Question 24

what is the mechanism for the absorption of the products of digestion by cells lining the ileum of mammals(amino acids)?

Answer 24

• absorbed via a co-transport
• sodium ions are actively transported out the ileum epithelial cells into the blood
• creates a sodium ion concentration gradient
• sodium ions diffuse from the lumen of the ileum into the epithelial cells through sodium-dependent transporter proteins carrying amino acids with them