digestion and absorption Flashcards
what is digestion?
large, insoluble molecules are broken down into smaller molecules which can move across cell membranes
what type of reaction is used during digestion?
hydrolysis
outline the digestion of carbohydrates.
amylase:
-a digestive enzyme that catalyses the breakdown of starch
-it works by catalysing the hydrolysis reactions that break the glycosidic bonds in starch to produce maltose
-it is produced by the salivary glands and the pancreas which releases it into the small intestine
membrane-bound disaccharidases:
-they are enzymes that are attached to the cell membranes of epithelial cells lining the ileum
-they help break down disaccharides into monosaccharide through hydrolysis of glycosidic bonds (sucrase, maltase and lactase)
the monosaccharides can be transported across the epithelial cell membranes in the ileum via specific transporter proteins
outline the digestion of lipids.
-lipase enzymes catalyse the breakdown of lipids into monoglycerides and fatty acids through the hydrolysis of ester bonds
-lipase is mainly made in the pancreas then they’re secreted into the small intestine
-bile salts are produced by the liver and emulsify lipids, meaning the cause the lipids to form small droplets
-several small lipid droplets have a bigger surface area than a single large droplet so gives lipase more area to work on
-once the lipid has been broken down by lipase, the monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles
outline the digestion of proteins.
-proteins are broken down by a combination of different peptidases
-endopeptidases hydrolyse peptide bonds within a protein
-exopeptidases hydrolyse peptide bonds at the terminal ends of proteins, removing single amino acids from proteins
-dipeptidases are exopeptidases that work specifically on dipeptides
-they are often located in the cell-surface membrane of epithelial cells in the small intestine
how are the products of digestion of carbohydrates absorbes?
-glucose is absorbed by active transport with sodium ions via co-transporter protein
-galactose is absorbed in the same way using the same co-transporter protein
-fructose is absorbed via facilitated diffusion through different transporter protein
how are the products of digestion of lipids absorbed.
-micelles help to move monoglycerides and fatty acids towards the epithelium
-micelles constantly break up and reform meaning they can ‘release’ monoglycerides and fatty acids allowing them to be absorbed
-whole micelles are not taken up across the epithelium
-monoglycerides and fatty acids are lipid soluble so can diffuse directly across the epithelial cell membrane
how are the products of digestion of proteins absorbed.
-sodium ions are actively transported out of epithelial cells into the ileum itself
-they diffuse back into the cells through sodium dependant transporter proteins in the epithelial cell membranes, carrying amino acids with them
what enzymes are involves in the digestion of carbohydrates?
amylase
membrane bound disaccharide such as maltase, lactase and sucrase
what molecules are used during the digestion of lipids?
lipase
bile salts
micelles
what enzymes are used during the digestion of proteins?
endopeptidases
exopeptidases
dipeptidases
