1: BIOLOGICAL MOLECULES - DIGESTION AND ABSORPTION Flashcards
Why does digestion happen?
digestion means that molecules can be easily absorbed from the gut into the blood to be transported around the body to be used by cells
What enzyme catalyses the breakdown of starch?
amylase
What are the sites of amylase production/use?
- salivary glands
- pancreas
What is the product of the digestion of starch?
maltose
What enzymes catalyse the breakdown of disaccharides?
disaccharidases
What are the sites of production/use of disaccharidases?
membrane bound in the ileum
What disaccharidase catalyses the breakdown of maltose?
maltase
What disaccharidase catalyses the breakdown of sucrose?
sucrase
What disaccharidase catalyses the breakdown of lactose?
lactase
What are the products of the digestion of maltose?
2 alpha glucose molecules
What are the products of the digestion of sucrose?
glucose + fructose
What are the products of the digestion of lactose?
glucose + galactose
What type of bond is hydrolysed in the digestion of polysaccharides/disaccharides?
glycosidic bonds
What enzymes catalyse the breakdown of polypeptides?
- exopeptidases
- endopeptidases
What bonds do endopeptidases break?
peptide bonds within the polypeptide chain
What bonds do exopeptidases break?
peptide bonds at the end of the polypeptide chain
What are the products of polypeptide digestion with endopeptidase?
2 shorter polypeptide chains
What are the products of polypeptide digestion with exopeptidase?
shorter polypeptide chain + 1 amino acid
What is the site of production/use of exopeptidases and endopeptidases?
the stomach
What enzymes catalyse the breakdown of dipeptides?
dipeptidases
What are the products of dipeptide digestion?
2 amino acids
What is the site of dipeptidase production/use?
membrane bound in the small intestine
What type of bonds are hydrolysed in the digestion of polypeptides and dipeptides?
peptide bonds
What enzyme catalyses the breakdown of lipids?
lipase
What is the site of lipase production/use?
the pancreas
What are the products of lipid digestion?
monoglycerides + 2 fatty acids
What type of bond is hydrolysed in the digestion of lipids?
ester bonds
What is the function of bile salts?
bile salts emulsify lipids (cause the lipids to form small droplets)
What organ produces bile salts?
the liver
What is the benefit of emulsifying lipids?
- several small lipid droplets have a larger surface area than a single large droplet (for the same volume of lipid)
- this means that the surface area available for lipase to work on increases
What happens after the lipids are broken down by lipase?
monoglycerides and fatty acids stick with the bile salts to from micelles
What is the function of micelles?
help products of lipid digestion to be absorbed
How are lipids absorbed?
- micelles move monoglycerides and fatty acids towards the epithelium
- because micelles constantly break up and reform they release monoglycerides and fatty acids
- monoglycerides and fatty acids are lipid soluble so they diffuse directly across the epithelial cell membrane
- monoglycerides and fatty acids form triglycerides (produced by SER)
- golgi body packages triglycerides into chylomicrons
- chylomicrons move from the epithelial cell into the lacteal by exocytosis
How are glucose and galactose absorbed?
glucose and galactose are absorbed across the ileum epithelium into the bloodstream by active transport via co-transporter proteins
How is fructose absorbed?
fructose is absorbed by facilitated diffusion
Describe the co-transport of glucose across the ileum epithelium (6 marks)
- Na^+ ions pumped out of epithelial cell by active transport/sodium-potassium pump into blood
- maintaining Na^+ ion conc gradient between lumen of ileum and epithelial cell
- glucose moves in with Na^+ ion into epithelial cell via co-transporter protein
- Na^+ ion moves down conc gradient whilst glucose moves against conc gradient
- glucose moves into blood by facilitated diffusion via carrier protein
How are amino acids absorbed?
- amino acids are absorbed via co-transport
- Na^+ ions are actively transported out of the ileum epithelial cells into the blood which creates an Na^+ ion conc gradient
- Na^+ ions can then diffuse from the lumen of the ileum into the epithelial cells through sodium-dependent transporter proteins, carrying the amino acids with them
