Digestion and absorption Flashcards
How are large biological molecules (polymers) broken down into smaller molecules (monomers)
Hydrolysis reaction - breaks bonds by adding water
What are carbohydrates (starch) broken down by? what are they broken down into? and what bonds are broken + what reaction does this?
Amylase, the digestive enzyme catalyzes the conversion of starch (polysaccharide) into maltose (a disaccharide)
And membrane-bound disaccharidases - enzymes attached to the cell membrane of epithelial cells lining the ileum - they break down disaccharides into monosaccharides (e.g. glucose) (these are transported via transporter proteins across the ileum)
What are lipids broken down by?
Lipase, with the help of bile salts
lipase catalyses the breakdown of lipids into monoglycerides + fatty acids + involves the hydrolyse of the ester bonds in lipids.
Where is amylase produced and released into?
Produced by salivary glands and released into mouth and produced by pancreas which releases amylase into the small intestines.
Where is lipase produced and released into?
produced in the pancreas, and released into small intestines
Where are bile salts produced + what do they do
Produced in the liver and emulsify lipids, causes the lipids to form small droplets
How do bile salts help lipid digestion?
As several bile salts have a larger surface area than a single large droplet, so the formation of bile salts increases the surface area of the lipid that lipase can work on - once the lipid has been broken down into monoglycerides and fatty acids, these stick to bile salts which form micelles.
What are proteins broken down by?
Endopeptidases and exopeptidases - these catalyze the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids,
Endopeptidases - where does it hydrolyse + examples of them
Hydrolyse peptide bonds WITHIN a protein
e.g. pepsin is a endopeptidase which is released into the stomach + only works in acidic conditions
Exopeptidases - where does it hydrolyse
Hydrolyse peptide bonds AT THE ENDS of protein molecule - they remove single amino acids from the protein. e.g. dipeptidases located on surface of epithelial cells in the small intestines
How are monosaccharides absorbed across the ileum epithelium into the bloodstream?
- Glucose absorbed by active transport with sodium ions via a co-transporter protein. Galactose is absorbed in same way using same co-transporter.
- Fructose is absorbed via facilitated diffusion through a different transporter protein.
How are monoglycerides and fatty acids absorbed across the ileum epithelium into the bloodstream?
- micelles help move monoglycerides and fatty acids towards the epithelium as micelles constantly break up and reform they 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 diffuse across phospholipid bilayer of epithelial membrane easily.
How are amino acids absorbed across the ileum epithelium into the bloodstream?
- amino acids are absorbed via sodium ions being actively transported out of the epithelial cells into the ileum. They then diffuse back into the cells through sodium-dependent transporter proteins in the epithelial cell membranes - carrying the amino acids with them.
