Digestion and Absorption Flashcards
what happens during digestion?
- large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes
what are the enzymes involved in the digestion of the carbohydrates in mammals?
- amylase
- membrane-bound disaccharidases
what is amylase?
- 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
how does amylase work?
- catalyses hydrolysis reactions that break glycosidic bonds in starch to produce maltose(disaccharide)
where is amylase produced?
- by the salivary glands, which releases amylase into the mouth
- by the pancreas which releases amylase into the small intestine
what are membrane-bound disaccharidases?
- they are enzymes attached to the cell membranes of epithelial cells lining the ileum
what do membrane-bound disaccharidases do?
- hydrolyse disaccharides into monosaccharides
- involves the hydrolysis of glycosidic bonds
what is involved in the digestion of lipids?
- lipase enzymes
- bile salts
what do lipase enzymes do?
- catalyse the breakdown of lipids in monoglycerides and fatty acids
- involves hydrolysis of ester bonds in lipids
where are lipases mainly made and secreted?
- made in pancreas
- secreted into small intestine where they act
where are bile salts produced?
liver
what is the role of bile salts?
- to emulsify lipids = cause lipids to form small droplets
- bile salts are not enzymes, important in lipids digestion
why are bile salts important?
- 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
what happens after lipids are broken down by lipase?
- monoglycerides and fatty acids associate with the bile salts to form a micelle
how are proteins broken down?
- combination of peptidases
- endopeptidase and exopeptidase
what do the peptidases do to the protein?
- catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids
what is endopeptidase?
hydrolyse the peptide bonds within the proteins
what is exopeptidase?
hydrolyse the peptide bonds on terminal amino acids of polypeptide molecules from endopeptidases
- they remove single amino acids from the protein at the end of the polymer chain
what are membrane-bound dipeptidases?
- exopeptidase that work on dipeptides
- hydrolyse the peptide bond between two amino acids
where are membrane- bound dipeptidases located?
- cell surface membrane of epithelial cells in a small intestine
what are micelles?
- help the products of lipid digestion to be absorbed
what is the mechanism for the absorption of the products of digestion by cells lining the ileum of mammals(monosaccharides)?
- 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
what is the mechanism for the absorption of the products of digestion by cells lining the ileum of mammals(monoglycerides and fatty acids)?
- 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
what is the mechanism for the absorption of the products of digestion by cells lining the ileum of mammals(amino acids)?
- 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
