Question

4.) The enzyme, pepsin, is one that hudrolvess proteins in the stomach, where the pH Is aboun 2 due to stomach acidx, into individual amino acids a) What would you expect to happen so the activity of the enzyme pepsin when in exits the stomach and enters the small imestine where the pi is about ? b.) Amylase is found in saliva where hydrolysis of starches begins. What would you expeet to happen to the activity of the enryme amylase when it enters the stomach? c.) What protein structure(s) is are) (primary, secondary, tertiary) disrupted by pepsin? d.) What protein structure(s) in amylase is(are) disrupted upon entering the stomach?

Answer 1

a) Pepsin works at acidic pH of about 2. This acidic pH is maintained in the stomach by Hydrochloric acid by parietal cells of stomach. But in the small intestine the pH is alkaline due to bicarbonate salts secreted by pancreas. So in the small intestine acidic pH is neutralised which also inactivates the pepesin as it works only in acidic environment.

b) Amylase acts on starch by breaking down the glycosidic bond to release simple sugars like glucose. Mostly salivary amylase work at neutral pH of about 7, but when it reaches stomach , it's acidic environment denature the structure of amylase and thus it is not able to work in stomach.

c) Pepsin is an endopeptidase which acts on peptide bond thus breaking polypeptide into smaller peptides. So primary structure can easily be broken by pepsin,in case of secondary and tertiary structures due to folding by hydrophobic,vanderwaal interaction, hydrogen bonds etc., The peptide bond is not easily Accessible to pepsin. Therefore to act on secondary and tertiary structures, peptide bond has to be accessible to pepsin so some of the folding interaction of the protein has to break.

d) When amylase enters the stomach it's activity is inactivated by the stomach acid. It gets denatured at acidic pH and it's shape changes which do not allow it to act on starch.