Digestion and Absorption: protein and lipids

Question 1

what is the enzyme called that hydrolyses proteins

Answer 1

protease

Question 2

explain the role of endopeptidases

Answer 2

-they hydrolyse internal peptide bonds within the polypeptide
-this produces many smaller / shorter polypeptide chains which increases the surface area for the next enzyme
-this makes digestion faster and more efficient

Question 3

explain the role of exopeptidases

Answer 3

-they hydrolyse the peptide bonds at the terminal ends of the polypeptide chain
-this produces dipeptides and single amino acids

Question 4

explain the role of dipeptidases

Answer 4

-embedded in the cell surface membrane of epithelial cells
-they hydrolyse single peptide bonds in the dipeptide to produce single amino acids
-these amino acids can now be absorbed by co-transport

Question 5

explain how amino acids are absorbed

Answer 5

-sodium ions are actively transported out of epithelial cells into the blood
-this creates a concentration gradient of sodium ions
-sodium ions and amino acids enter the epithelial cell by facilitated diffusion using co-transporter proteins. This co-transporter protein has two binding sites with one being specific to sodium and the other amino acids
-amino acids then move into the blood by facilitated diffusion

Question 6

explain the process of lipid digestion and absorption

Answer 6

-lipid droplets are mixed with bile salts to form smaller droplets (emulsified)
-this increases the surface area for faster hydrolysis by lipase
-triglycerides are hydrolysed into glycerol, fatty acids and monoglycerides
-bile salts, glycerol and fatty acids form micelles
-the micelles make fatty acids solublee in water and bring them to the surface of the epithelial cell membrane. This maintains a higher concentration relative to the epithelial cells
-fatty acids enter the epithelial cells by simple diffusion
-at the smooth endoplasmic reticulum the fatty acids and glycerol are recombined to form triglycerides
-at the Golgi apparatus the triglyceides are modified, proteins are added to form lipoproteins (chlyomicrons) and packaged into vesicles
-chlyomicrones are transported into a lymph vessel by exocytosis. They then enter the blood