Digestion and abs：练习题

• a.

  Endopeptidases act first in the stomach, then bile salts emulsify the protein for exopeptidase action in the ileum.

• b.

  Membrane-bound dipeptidases act first in the duodenum, followed by exopeptidases and endopeptidases in the ileum.

• c.

  Endopeptidases hydrolyse internal peptide bonds, followed by exopeptidases and then membrane-bound dipeptidases.

• d.

  Exopeptidases hydrolyse peptide bonds at the ends of the chain, followed by endopeptidases and then membrane-bound dipeptidases.

• a.

  The active transport of \(Na^{+}\) ions out of the cell by the sodium-potassium pump; glucose then leaves the cell via facilitated diffusion.

• b.

  The osmosis of water carrying \(Na^{+}\) ions out of the cell; glucose then enters the blood via a membrane-bound disaccharidase.

• c.

  The facilitated diffusion of \(Na^{+}\) ions into the cell; glucose then leaves the cell via active transport using ATP.

• d.

  The active transport of \(Na^{+}\) ions into the cell by the sodium-potassium pump; glucose then leaves the cell via simple diffusion.

• a.

  To emulsify large lipid droplets into smaller droplets, increasing the surface area for lipase action.

• b.

  To provide an acidic environment required for the optimal activity of pancreatic lipases.

• c.

  To decrease the surface area of lipid droplets to protect them from acidic gastric juices.

• d.

  To hydrolyse the ester bonds in triglycerides to produce fatty acids and glycerol.

• a.

  Micelles are large lipid droplets found in the lumen; chylomicrons are the smaller droplets formed after emulsification by bile salts.

• b.

  Micelles are formed within the epithelial cells and transport triglycerides to the Golgi apparatus to be packaged into chylomicrons.

• c.

  Micelles transport triglycerides directly into the blood; chylomicrons transport them into the lymphatic system through the cell-surface membrane.

• d.

  Micelles facilitate the movement of fatty acids and monoglycerides to the epithelial cell membrane; chylomicrons are formed inside the cell for transport into lacteals.

• a.

  Endopeptidases act as co-factors for exopeptidases, increasing the affinity of the active site for the peptide bond.

• b.

  Exopeptidases can only bind to the substrate once endopeptidases have removed the R-groups from the central amino acids.

• c.

  Endopeptidases hydrolyse internal peptide bonds, creating more terminal ends for exopeptidases to act upon.

• d.

  Endopeptidases lower the activation energy of exopeptidases by partially denaturing the tertiary structure of the protein.

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。