digestion and absorption (3.3) Flashcards
(21 cards)
what is digestion
large insoluble molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes
what enzymes are used in carbohydrate digestion and where are they found
-amylase in the mouth/salivary glands
-maltase,sucrase,lactase in the small intestine
what are the substrates and products of carbohydrate digestive enzymes
-amylase hydrolyses starch into smaller polysaccharides
-maltase hydrolyses maltose into 2 glucose molecules
-sucrase hydrolyses sucrose into glucose and fructose
-lactase hydrolyses lactose into galactose and glucose
what are the 3 enzymes proteins can be hydrolysed by
-endopeptidases
-exopeptidases
-dipeptidases
what do endopeptidases do
hydrolyse peptide bonds between amino acids in the middle of the polymer chain
what do exopeptidases do
hydrolyse peptide bonds between amino acids at the end of the polymer chain
what do dipeptidases do
hydrolyse peptide bonds between 2 amino acids
where does protein digestion occur
stomach continues in duodenum finishes in ileum
how are lipids digested
lipids are digested by lipase and the action of bile salts
where is lipase produced and what does it do
-produced in pancreas
-hydrolyses ester bond in triglycerides to form monoglycerides and fatty acids
where are bile salts produced and what do they do
-produced in liver
-emulsify lipids into many tiny droplets which creates a larger sa for lipase to work on , enabling faster hydrolysis of lipids
-also form micelles
what are micelles
water soluble vesicles formed of fatty acids, monoglycerides and bile salts
what is the purpose of micelles
-they deliver the fatty acids and monoglycerides to the epithelial cells of the ileum
-micelles make fatty acids more soluble in water so they break down when they reach the ileum
where does absorption occur
occurs in cells lining the ileum
how is the ileum wall adapted for absorption
-covered in villi which have microvilli
-villi surrounded by capillaries
-thin wall
how are monosaccharides and amino acids absorbed
co transport
describe co transport process
-active transport of sodium ions from epithelial cell into blood to lower sodium ion concentration inside of cell to generate a sodium ion concentration gradient between the ileum and epithelial cell
-sodium ions move into the cell from the ileum by faciliated diffusion carrying an amino acid or glucose molecule along with them via a co transporter protein
-glucose/amino acid concentration in the epithelial cell will then increase and glucose will enter the blood by faciliated diffusion.
describe the first step of lipid absorption
-when micelles encounter the ileum epithelial cells they break down and due to the non polar nature of fatty acids and monoglycerides they simply diffuse across the cell surface membrane to enter the epithelial cells
what happens once the fatty acids and monoglycerides are in the cell
the fatty acid chains and monoglycerides recombine to create triglycerides in the endoplasmic reticulum
what is the golgi apparatus role in lipid absorption
-the triglycerides are modified by adding a protein to create chylomicrons
-the chylomicrons are then packaged into golgi vesicles
-these vesicles move to the cell membrane and fuse so they are extruded from cell by exocytosis
howdo chylomicrons enter the bloodstream
enter a lacteal which will eventually lead to the chylomicrons entering the bloodstream
