Digestion and Absorption Flashcards
Explain the process of digestion
Large insoluble biological molecules are broken down into smaller soluble molecules which can be then absorbed into the bloodstream from the gut to be used by the body
Which enzyme hydrolyses starch
Amylase hydrolyses starch into the disaccharide maltose. This involves the hydrolysis of the glycosidic bonds in starch
Where is the digestive enzyme amylase produced
In the salivary glands (which releases amylase into the mouth) and in the pancreas (which releases amylase into the small intestine)
What are membrane bound disaccharidases
Enzymes which are attached to the cell membrane of epithelial cells lining the ileum. They help break down disaccharides into monosaccharides
How are monosaccharides transported across the cell membrane of ileum epithelial cells
Via specific transporter proteins
How are lipids hydrolysed
By lipase and bile salts
Lipase enzymes catalyse the breakdown of lipids into monoglycerides and fatty acids. This involves the hydrolysis of the ester bonds in lipids
Where are lipases made
In the pancreas but they work in the small intestine
Where are bile salts made and what are their functions
Produced by the liver and they emulsify lipids causing them to form small droplets
Why are bile salts important in lipid digestion
Several small lipid droplets have a bigger surface area so the formation of small droplets greatly increases the surface area of lipid that’s available for lipases to work on. Once the lipid has broken down , the monoglycerides and fatty acids stick with the bile salts to form tiny structures called micelles
How are proteins broken down
By a combination of different proteases (or peptidases) These are enzymes that catalyse the hydrolysis of proteins into amino acids by hydrolysing the peptide bonds between amino acids
What are the functions of endopeptidases
endopeptidases act to hydrolyse peptide bonds within a protein
Trypsin and chymotrypsin are examples they’re synthesised in the pancreas and secreted into the small intestine
Pepsin is another example that is released into the stomach by cells in the stomach lining
Pepsin only works in acidic conditions - provided by the hydrochloric acid in the stomach
What are the functions of exopeptidases
exopeptidases act to hydrolyse peptide bonds at the ends of the protein molecules. They remove single amino acids from proteins. Dipeptidases are exopeptidases that work specifically on dipeptides. They act to separate the two amino acids that make up a dipeptide by hydrolysing the peptide bond between them. Dipeptidases are often located on the cell surface membrane of epithelial cells in the small intestine
How is glucose absorbed across cell membranes
By active transport with sodium ions via a co-transporter protein. Galactose is absorbed in the same way using the same co-transporter protein
How is fructose absorbed across cell membranes
Via facilitated diffusion through a different co-transporter protein to glucose and galactose
How are monoglycerides and fatty acids absorbed across cell surface membranes
Micelles help to move monoglycerides and fatty acids towards the epithelium because 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 the epithelium. Monoglycerides and fatty acids are lipid-soluble so can diffuse directly across the epithelial cell membrane
