enzymes and digestion

what does digestion involve?

• the breakdown of large, biological molecules into smaller molecules.

• the smaller molecules can then be taken up by the cells and used for a number of function

what is hydrolysis?

• the reaction that breaks down large, biological molecules

• the reaction requires water and splits larger molecules into their smaller components

• these smaller molecules (e.g- glucose) can easily diffuse into cells or be transported using protein channels

products of hydrolysis?

• hydrolysis of proteins produces amino acids

• hydrolysis of carbs produces disaccharides and monosaccharides

• hydrolysation of lipids produces fatty acids and monoglycerides

where does the digestion of carbs begin and what enzyme is involved?

• begins in the mouth, and the enzyme amylase is involved

• amylase is an enzyme that is produced in the salivary glands and the pancreas

• amylase catalyses the hydrolysis of starch into maltose

• hydrolysis of carbs breaks bonds called glycosidic bonds

what are membrane-bound disaccharides?

• enzymes in the cell membranes of the epithelial cells in the ileum (small intestine)

• membrane-bound disaccharidases catalyse the hydrolysation of disaccharides into monosaccharides

how are monosaccharides transported into the epithelial cells in the ileum?

• using transporter proteins

  • glucose and galactose are transported by co-transporter proteins

  • fructose is absorbed by facilitated diffusion

• once inside the cells, monosaccharides can be used in respiration

what is lipase?

• an enzyme that is produced by the pancreas and is released into the small intestine

• lipase hydrolyses lipids into fatty acids and monoglycerides

• hydrolysis of lipids breaks bond called ester bonds

what are bile salts?

• they are produced by the liver

• they also help digest lipids by forming small lipid droplets called micelles

• the process of forming micelles is called emulsification

• the many micelles have a larger surface area than a single larger micelle

• this allows the lipids to be hydrolysed by lipase more quickly

micelles?

• the micelles allows the monoglycerides and fatty acids to be absorbed by the epithelial cells in the ileum

• the monoglycerides and fatty acids diffuse through the cell surface membrane into the cell cytoplasm

what are endopeptidases?

• they are enzymes that catalyse the hydrolysis of bonds within a protein to amino acids

• hydrolysis of proteins breaks bonds called peptide bonds

• examples of endopeptidases include:

  • trypsin

  • chymotrypsin

  • pepsin

• trypsin and chymotrypsin are released by the pancreas into the small intestine

• pepsin is released into the stomach

what are exopeptidases?

• they are enzymes that catalyse the hydrolysis of peptide bonds at the ends of proteins

  • e.g- dipeptidases hydrolyse the peptide bond between 2 amino acids

what are co-transporter proteins needed for?

• they transport amino acids into the epithelial cells in the ileum

what happens after larger molecules are hydrolysed into monomers?

• they are absorbed by the cells

active transport of sodium ions?

• sodium-dependent co-transporter proteins are located in the epithelial cell membranes

• the co-transporter proteins actively transport sodium ions into the blood

• this causes the concentration of sodium ions in the epithelial cells to decrease

diffusion of sodium ions?

• the decreased concentration of sodium ions in the epithelial cells causes sodium ions in the ileum to diffuse down their concentration gradient

• the sodium ions diffuse through a co-transporter protein in the cell surface membrane

binding of amino acids and sugars?

• when sodium ions bind to a co-transporter protein, amino acids, or monosaccharides also bind to the protein

• binding of amino acids or monosaccharides causes the transporter protein to undergo a conformational change

• the amino acids or monosaccharides, along with the sodium ions are transported into the epithelial cell cytoplasm

• once inside the epithelial cells, the amino acids or monosaccharides can then be used inside the epithelial cells or absorbed into the bloodstream

formation of micelles?

• after larger lipid molecules have been broken down into monoglycerides and fatty acids, bile salts are secreted by the liver

• the bile salts associate with the monoglycerides and fatty acids to form micelles

• micelles are circular formations that are made up of phospholipid tails

incorporation of micelles?

• the micelles move through the ileum and come into contact with the epithelial cells

• the micelles incorporate themselves into the epithelial cell surface membrane and are absorbed