digestion Flashcards
what is the definition of carbohydrate digestion?
the process by which large, insoluble starch is hydrolysed by enzymes to produce disaccharides and monosaccharides by breaking glycosidic bonds.
where is starch digested?
starch is large and insoluble and is digested in the mouth and small intestine to produce small, soluble molecules that can be absorbed into the blood.
what two locations is starch broken down into maltose?
-mouth by salivary amylase
-small intestine by pancreatic amylase
where is salivary amylase made and secreted? what does it do?
made in salivary glands and secreted into the mouth
catalyses hydrolysis reaction that breaks glycosidic bonds connecting glucose units in starch
it does this by forming enzyme-substrate complexes and lowering activation energy
how does amylase lower the activation energy to catalyse the hydrolysis of starch?
when starch binds to active site of amylase, the active site changes shape to fit the substrate and this puts a pressure on the glycosidic bond, making it easier to break.
where is pancreatic amylase made and secreted? what does it do?
made in the pancreas and secreted in the small intestine.
catalyses the hydrolysis of glycosidic bonds connecting glucose units in starch.
how is maltose broken down into glucose?
the enzyme maltase which is in the cell membrane of the small intestine epithelial cells
maltase catalyses the hydrolysis that breaks the glycosidic bond between glucose units in maltose
what is the product of hydrolysis of maltose?
small, soluble glucose units that can be absorbed into the blood
what do endopeptidases do?
catalyse the hydrolysis of peptide bonds in the middle of large polypeptide chains into smaller polypeptide chains.
what do exopeptidases do?
catalyse hydrolysis of peptide bonds at the end of polypeptide chains to make dipeptides and some single amino acids.
what do dipeptidases do?
catalyse hydrolysis of peptide bonds between two amino acids (dipeptides) to release singular amino acids.
what is the general name for enzymes that break down proteins?
proteases
where are pepsin and trypsin released?
pepsin- stomach, optimum pH of 2
trypsin- pancreas, optimum pH of 8 ACTS IN SMALL INT
where do the enzymes of protein digestion act?
endopeptidases- stomach and small intestine
exopeptidases- small intestine (duodenum)
dipeptidases- small intestine (duodenum)
where are exopeptidases and dipeptidases found?
in the cell membrane of small intestine epithelial cells
pepsin and trypsin are first released by cells in an inactive form, why?
to prevent auto digestion- stop enzymes breaking down proteins inside the cell
how are small intestine epithelial cells adapted for digestion?
-many mitochondria = high rates of resp= lots of ATP= more protein synthesis= more enzymes for digestion
-lots of ribosomes for protein synthesis
-lots of rough ER for transport of proteins
-lots of Golgi to modify proteins and transport them to cell surface
where does lipid digestion take place?
small intestine
how is the optimum pH provided for digestion of lipids?
bile is alkaline (sodium hydrogen carbonate) and it neutralises the stomach acid to provide the optimum pH for lipase to act
where is bile produced/ stored/ acts?
produced in the liver
stored in gall bladder
released into the duodenum
why do triglycerides have a small surface area to volume ratio?
they are non-polar and so form large lipid droplets
what does bile contain and what do these do?
bile salts are responsible for emulsification
describe the structure of bile salts?
hydrophobic tail and negatively charged hydrophilic head
describe bile salts role in emulsification?
mechanical digestion in the stomach breaks down large fat droplets into smaller ones
bile salts attach to droplets with hydrophobic tails within the droplets and hydrophilic heads on the outside, associating with water
the negative charge on the head of the bile salts repels droplets from each other so they don’t re-join
what is the purpose of emulsification?
gives droplets a large surface area to volume ratio
more surface for lipase to act on and so faster hydrolysis of triglycerides
describe lipase role in digestion of lipids?
catalyses the hydrolysis reaction that breaks the ester bond in a triglyceride to produce 2 fatty acid chains and a monoglyceride
what happens to the fatty acid chains and monoglycerides after digestion?
they interact with bile salts to form micelles
the bile salts give greater solubility
the micelle holds a high concentration of fatty acids and monoglycerides
where do these micelles go?
go to the surface of ileum epithelial cells where they break down, allowing fatty acids and monoglycerides to diffuse into the epithelial cells
what allows fatty acids and monoglycerides to diffuse into ileum epithelial cells?
higher conc of them in the micelle than within the cell, and they are lipid soluble so move through bilayer via simple diff.
what is the weird thing that happens to the fatty acids and monoglycerides once they are absorbed into the small intestine?
they are re-synthesised into triglycerides!
explain how triglycerides are re-synthesised in the epithelial cells?
fatty acids and monoglycerides move into smooth ER where condensation reaction takes place
COOH of fatty acids reacts with OH on glycerol to form ester bonds
transported to Golgi via vesicles- modified by adding proteins and cholesterol to form CHYLOMICRONS
what are chylomicrons?
triglycerides modified by being combined with proteins and cholesterol
where do chylomicrons go inside the epithelial cell?
vesicles containing them move to the surface of the epithelial cells and fuse with the membrane, releasing chylomicrons via exocytosis
after leaving the cell, where do chylomicrons go?
enter the lacteal of a villi and are transported through the lymphatic system
what does the lymphatic system drain into?
the subclavian vein in the neck, so triglycerides enter blood.
what are the benefits of the many villi and microvilli to the small intestine?
more membrane= more carrier and channel proteins= faster rate of facilitated diffusion and active transport
how do villi lead to faster rate of diffusion?
one cell thick walls = short diffusion pathway= faster rate
increase surface area
capillary network in every villi= good blood flow and maintains conc gradient to absorb products of digestion via diffusion
how do lacteals in every villi help function?
having them in EVERY villi increases rate of absorption of chylomicrons
lacteals are wider than capillaries so chylomicrons can be absorbed, which are too big to go into capillaries
