A level biology

• what is the purpose of digestion that large biological molecules arenhydroylsed into smaller molecules thta can be absorbed across cell memebranes
• how are lipids digested - triglyceride are digested in the small intestine by lipase, which is secreted from the pancreas
• how does lipase work - in the small intestine the lipase triglyceride molecules to a monoglyceride and 2 fatty acids, and the ester bonds are hydroylsed to release the fatty acids
• what is a monoglyceride one glycerol bonded to one fatty acid
• what is emulsification this is the process of creating an emulsion. an emulsion is a mixture of two or more liquids that dont normally mix.
• what are bile salts - they emulsify lipid globules into an emulsion of many smaller droplets.
• why are bile salts useful - the droplets are smaller than globules, which each have a larger surface area to volume ratio, to now there is a greater surface area for lipase to work on, so allows faster digestion and hydrolysis of lipids - digestion creates even smaller droplets called micelles.
• what are micelles they are smaller droplets, that carry the monoglycerides and fatty acids to the cell surface membrane of the ileum epithelial cells for absorption.
• micelles lipid droplets that have their triglyceride digested
• what is the role of micelles in the absorption of the lipids The products of triglyceride digestion (fatty acids, monoglycerides) remain in association with bile salts to form tiny droplets called micelles; Because of the bile salts, micelles make the fatty acids and monoglycerides soluble in water; The micelles diffuse to and contact with the cell surface membrane of the ileum epithelial cells and break apart; This releases the non-polar monoglycerides and fatty acids, which diffuse straight through the phospholipid bilayer into the cell. Bile salts stay in the lumen of the ileum to be reused...
• how are lipids now digested once in the cell Once inside the cell, the monoglycerides and fatty acids are recombined in the smooth endoplasmic reticulum (not shown on diagram) to make triglycerides. The triglycerides are then sent to the Golgi apparatus via vesicles. The Golgi apparatus processes triglycerides into structures called chylomicrons, that also contain protein. Chylomicrons leave the Golgi apparatus via vesicles. The vesicles move to and fuse with the cell-surface membrane at the base of the cell, causing the chylomicrons to leave the cell. They chylomicrons are taken up by near...
• what is the function of the smooth endoplastic reticulum in lipid digestion - the monoglycerides and fattu acids are recombined to make triglyceride.
• what is the role of the golgi appartus in the digestion of lipids - they form triglycerides into structure called chylomicrons, they also contain proteins
• where to the chylomicrons go after the golgi appartus - they are enclosed into a vesicle and move out and fuse with the cell - surface membrane at the base of the cell, then they are taken up by the lymph capillaries
• diagram of the absorption of lipids
• diagram of chylomicrons
• what is the process by which fatty acids and glycerol enter the intestinal epithelial cell diffusion
• explain the advantages of lipid droplets and micelles formation
• how is starch hydroylsed Remember: anything ending in –ase is an enzyme. Amylase is an enzyme found in saliva in the mouth and is also secreted into the small intestine. Starch is hydrolysed to maltose by amylase. Maltose is hydrolysed to glucose molecules by a membrane-bound disaccharidase called maltase. Disaccharidase is the general term for any enzyme that hydrolyses a disaccharides into monosaccharides.
• Describe the complete digestion of starch by a mammal. (4) 1. Hydrolysis; 2. (Of) glycosidic bonds; 3. (Starch) to maltose by amylase; 4. (Maltose) to glucose by disaccharidase/maltase; 5. Membrane-bound (disaccharidase/maltase); Other than 5., do not penalise incorrect site for digestion or incorrect site of enzyme production Accept microvilli for membrane 4 max
• what is the epithelium a this tissue layer used to line structures in the body. membrane bound disaccharideases are attached to the cell surface membrane of ileum epithelial cells, and it makes up the bulk of the small intestine
• Why are some digestive enzymes membrane bound? Prevents the enzymes being carried away from the ileum with any remaining food and becoming lost in the faeces.
• Why aren’t all digestive enzymes membrane bound? Most digestive enzymes (e.g. lipase, amylase, peptidases) are free in the ileum lumen. This allows them to mix fully with their substrate, which is important for the larger substrates e.g. starch.
• what are some other membrane bound disaccahridase Lactase hydrolyses: Lactose to glucose and galactose Sucrase hydrolyses: Sucrose to glucose and fructose
• what are the types of enzymes involved in protein digestion Like all digestion, this involves hydrolysis Three types of enzyme involved Endopeptidases: hydrolyse peptide bonds between specific amino acids in the middle of a polypeptide Exopeptidases: hydrolyse peptide bonds between specific amino acids at the ends of a polypeptide Dipeptidases: hydrolyse the peptide bond in a dipeptide
• the role of different enzymes
• what is a dipeptide two amino acids bonded together by a peptide bond
• what are dipeptidases - they are atttached to the surface membranes of the cell lining of the small intestine - they hydroylse dipeptides into amino acids - the final products or protein digestion are amino acids, which are absorbed by the cells lining of the ileum of the small intestine
• the co-transport of glucose from the ileum lumen to the blood Sodium ions pass from the lumen into the epithelial cell by facilitated diffusion through a carrier protein; As the sodium ions pass through this carrier protein, the protein changes shape so that glucose can be simultaneously brought in against its concentration gradient, a process called co-transport; Glucose leaves to the blood by facilitated diffusion through a carrier protein at the base of the cell; Sodium ions actively transported to blood out of base of epithelial cell by a carrier protein; This removal of sodium ions mainta...
• Describe the mechanism for the absorption of amino acids in the ileum. (4) Co-transport of amino acids with sodium ions (into cell); Sodium ions actively transported from cell to blood/capillary/tissue fluid; Creating sodium ion concentration/diffusion gradient; Facilitated diffusion of amino acid into blood/capillary; Accept described role of channel/carrier proteins for ‘facilitated’ 4 max