Unformatted text preview: H.2.5. Outline the role of membrane-bound enzymes on the surface of epithelial
cells in the small intestine in digestion. Maltese is a membrane—bound enzyme. it functions in the biochemical pathway
of digesting starch: starch Hamylase —> maltose
maltosea maltase —>2 glucoses Maltese is in the right place where maltose is hydrolyzed to glucose and glucose
is absorbed. H26. Outline the reasons for cellulose not being digested in the alimentarv
canal Animals don’t produce cellulase, the enzyme that breaks down cellulose.
Herbivore mammals have intestinal bacteria that produce cellulase. The amount
of nutrients from plant material is so small that animals spend most of their time
grazing. Humans lack cellulose-breaking bacteria and cellulose is not digested. Role of
fiber. H.2.7. Explain why pepsin and trypsin are initially synthesized as inactive
precursors and how they are subseguently activated. Pepsin and trypsin are proteases. To avoid these proteases to digest ourselves,
pepsin and trypsin are initially synthesized in inactive form i’zymogens). Pepsin is released as pepsinogen (44 additional amino acids). After crossing the
mucus layer of the stomach, pepsinogen enters an acidic medium. HCI cuts the
additional amino acid chain and pepsinogen is transformed into pepsin. Trypsin is produced as trypsinogen in the pancreas and enters the duodenum.
When the chime arrives in the duodenum, enterokinase is produced by duodenal
glands. Enterokinase converts trypsinogen into trypsin. H.2.9. Explain the problem of lipid digestion in a hydrophilic medium and the role
of bile in overcoming this. Lipids are insoluble in water. Lipases can act only in the outermost part of lipid
drops in the chime. Bile is an emulsifier. it breaks lipid globules into smaller droplets, allowing more surface area for digestion by lipases.
The hydrophilic amino acids of lipase make the enzyme water soluble. The active site of the enzyme contains only hydrophobic amino acids, allowing the binding
of the lipid molecule to the site. ...
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- Summer '10