Digestion Flashcards
Definition of digestion
Large insoluble biological molecules in food are hydrolysed into smaller, soluble molecules that can be absorbed across the cell membranes into the bloodstream and delivered to cells
What do the small soluble molecules used for
provide cells with energy
build other molecules for cell growth, repair and function
Process of digestion structures
1) Mouth
2) Salivary Glands
3) Oesophagus
4) Stomach
5) Small intestine
6) Large intestine
7) Rectum
8) Anus
Two types of digestion
Physical breakdown
Chemical digestion
Physical breakdown
Food churned by muscles in stomach wall and teeth in mouth
Provides surface for chemical digestion
What is hydrolysis
Splitting up of molecules adding water to the chemical bonds that hold them together
How do digestive enzymes function
Hydrolysis
What enzymes digest carbohydrates, lipids, proteins
Carbohydrases
Lipases
Proteases
Where is amylase produced
Mouth and pancrease
What enzyme hydrolyses starch
amylase
Process of the breakdown of starch
1) Amylase produced in mouth that pancreas
2) Amylase hydrolyses glycosidic bonds, producing maltose
3) Maltose is hydrolysed into a-glucose using maltase
Where is maltase produced
Ileum
Process of carbohydrate digestion
1) Saliva enters mouth from salivary gland mixed during chewing
2) Salivary amylase hydrolyses starch into maltose, containing mineral salts to maintain pH at neutral
3) Food swallowed and enters stomach. Acid denatures amylase preventing further hydrolyses of starch
4) Food enters small intestine and mixes with pancreatic juice
5) Containing pancreatic amylase that hydrolyses starch into maltose. Alkaline salts maintain pH so amylase can function
6) Muscles in intestine wall push food along ileum to produce maltase
7) Maltase hydrolysed to alpha glucose
Where are alkaline salts produced
Intestinal wall and pancreas
What hydrolyses sucrose
Sucrase
Hydrolyses glycosidic bond to produce glucose and fructose
What hydrolyses lactose
Lactase
produce glucose and galactose
Where are lipases produced
Pancreas
What do lipases do
Hydrolyse ester bonds in triglycerides to form fatty acids and monoglycerides
How are lipids digested
Emusification process where Lipids split into micelles by bile salts
Increasing SA of lipid for lipases to act on
Where are bile salts produced
Liver
What enzymes digest protein
Peptidases (proteases)
3 types of peptidases
Endopeptidases
Exopeptidases
Dipeptidases
Endopeptidases
Hydrolyse peptide bonds between amino acids and central region of a protein molecule forming series of peptide molecules
Exopeptidases
After endopeptidases act, exo hydrolyse peptide bonds on terminal amino acids of peptide molecule
Releasing dipeptides and single amino acids
Dipeptidases
After endo and exo
Hydrolyse bond between two amino acids of a dipeptide
Part of cell-surface membrane of epithelial cells lining in ileum
What does the ileum have
Villi
What do villi give an advantage to
Increased surface area, increasing rate of absorption
What advantages do the villi give in digestion
- Increase SA for diffusion
- Thin = reduced distance for diffusion
- Contains muscle = maintain diffusion gradient because movement mixes contents of ileum, once absorbed new products replace old ones
- Rich blood supply = carry away absorbed molecules, maintaining diffusion gradient
- Villi have microvilli = increase SA further
What are micelles
Monoglycerides and fatty acids (from a lipid droplet) with bile salts
What happens to micelles
Monoglycerides and fatty acids are released (micelles just transport them to the small intestine)
How can micelles be transported to the ileum
Micelles are non-polar and so can diffuse across cell surface membrane into epithelial cells
What happens once the micelles break down into monoglycerides and fatty acids
Monoglycerides and fatty acids diffuse into epithelial cell and are transported to the endoplasmic reticulum
They recombine to form triglycerides
What do the newly formed triglycerides do
Form chylomicron when the triglycerides associate with cholesterol and lipoproteins
What do chlymicrons do
Transport the lipids
What do chylomicrons do
Move out of the epithelial cells by exocytosis
Enter lacteals (lymphatic capillaries) found in the centre of the villus
Chylomicrons pass via lymphatic vessels into the blood stream
What happens to the triglycerides in the chylomicrons in the blood stream
Triglycerides are hydrolysed by enzymes in the endothelial cells of blood capillaries
Where they can diffuse into cells
Process of how triglycerides are absorbed
1) Micelles from a lipid droplet break down into monoglycerides and fatty acids
2) They transported to the endoplasmic reticulum and combined to form triglycerides
3) Triglycerides associate with cholesterol and lipoproteins to form chylomicrons
4) Chylomicrons move out of epithelial cells by exocytosis and enter lacteals
5) the chylomicrons pass through the blood system and are hydrolysed by enzymes in the endothelial cells where they diffuse into cells
What is digestion
Large insoluble biological molecules in food are hydrolysed into smaller, soluble molecules that can be absorbed across the cell membranes into blood stream and delivered to cells
What are the three main types of enzymes
Carbohydrases proteases and lipases
How are carbohydrates digested (process) by amylase
1) Amylase hydrolyses starch into maltose in mouth and small intestine
2) Maltase hydrolyses maltose into glucose
3) Amylase in salivary glands, pancrease and small intestine
4) Maltase found in CSM of epithelial cells linign small intestine
5) Sucrase and lactase hydrolyse sucrose and lactose allowing absorption of monosaccharides into epithelial cells of small intestine which is passed into the blood stream
Digestion of proteins by proteases
1) Protein digestion begins in stomach
2) Endopeptidase hydrolyses peptide bonds in proteins and HCl acid released so pH in stomach is low and acidic.
3) Fluid secreted by pancreas travels to small intestine and neutralises acid to increase pH.
4) Pancreatic juice contains endopeptidases (hydrolyse bonds in middle of polypeptide chains) producing dipeptides
And exopeptidases hydrolyse at ends of polypeptide chains to produce dipeptides
There are also dipeptidase enzymes in CSM that hydrolyse dipeptides into amino acids and released into cytoplasm of cell
Summary of how proteins are digested
Protein + endopeptidase = polypeptides
Polypeptides + exopeptidase = dipeptides
Dipeptides + dipeptidase = amino acids
Emulsification of lipids
1) Stomach turns fatty liquid into fat droplets
2) Fatty liquid arrives in small intestine, bile is secreted from gallblader
3) Bile salts + fatty liquid breaks fatty droplets into smaller ones by emulsification
(Increases SA of fatty droplets for digestive enzymes)
Digestion of lipids
Lumen of small intestine
Lipase breaks fown lipids to glycerol and fatty acids
Lipase produced in pancreas and secreted into small intestine by pancrease
Summary of both lipid digestion
Lipids + bile salts -> emulsified lipids + lipase -> fatty acids and glycerol
Large fat globule + emulsification -> small fat droplets + dugestion -> fatty acids and glycerol
Factors affecting enzyme reaction rates practical
1) Add iodine to spotting tile
2) Add amylase and buffer to test tube, mux then add starch solution
3) start stopwatch
4) After 10 secs add a drop of solution to iodine in spotting tile
5) Repeat every 10 seconds until iodine doesnt change colour
6) Repeat steps 1-5 using buffer solutions of differen pH
Absorption of amino acids
Facilitated diffusion:
-Amino acid co-transport proteins in cell surface membrane of epithelial cells in ileum
-1 Na+ enters cell, 1 amino acid transport out
-Diffuse across epithelial cells and into capillaries
-Conc gradient of Na maintained by active transport of Na+ out of cell and into blood via sodium potassium pumps
Absorption of monosaccharides
1) Glucose carrier proteins co transport sodium ions and glucose by facilitated diffusion into epithelial cells
2) Glucose diffuse across apithelial cells and enter capillary
3) Conc of Na+ maintained by actively transporting sodium ions out of epithelial cells in blood
What do micelles do to absorb lipids
Micelles are fatty acids and monoglycerides + phospholipids and bile salts
Micelles break down and are added to fatty acids and monoglycerides to dissolve small intestine solution surrounding epithelial cells
What do the short and long lipid chains do to be asborbed
Short = move directly into blood by diffusion
Long = recombine with monoglycerides and glycerol forming triglycerides in endoplasmic reticulum
How are triglycerides absorbed
Packed into chylomicrons
Chylomicrons enter bloodstream via lacteals
