pH levels and enzymes question.?

Question

i am kinda confused.. i knw tht enzymes are affected by the level of pH. a pH level too low or too high will denature it. but in pepsin's case, it is adapted to work in low pH levels.. in the acidic conditions of the stomach. but tht is wht my Cambridge textbook says.. wht i dont get is, tht if the conditions of the stomach are acidic so how is the pH level they r adapted in working with low?? isnt it supposed to be high cuz of the acidic conditions? is it tht the more low the pH level the more acidic the pH level is?

Thxx. pls help!

Answer 1

Hi there.....good question...
I did ask myself the very same question when I was a medical undergraduate.....Then I discovered, that although ALL enzymes are proteins, not all of them had the same structyre....you see,,,the acidic enzymes (like pepsin, ptialin, etc), have more acidic amonoacid (more carboxyls free) like histidine, glycine etc..
The enzymes that are alkaline resistant (acting above Ph 8 for example, like trypsin, chymotrypsin, lactase, ribonuclkease etc, that predominate in the small intestine, are alkalinized near 7 by the bile secretions, (alkaline), and panvreatic bicarbonate, bringing the Ph towards 7- 9.... and contain more "amonia" like or alkaline aminoacids in their composition, , such as glutamine, asparagine, etc.-

An then I discovered that different enzymes, have different Pk, that is, the number that points to the different affinity of enzymes for substrate, according to the Michaelis Menten equation....Pk = 1 when the amount of enzyme and substrate in the reaction are the same....
The lower the Pk, the less afinity there will be, and Pk values will be under "zero"....and the Ph has a lot to do with this-...

On the other hand, enzymes, will be digested themselves at the end of the cycle, so, that being proteins, they will be digested by other enzymes,(recycling its aminoacids). that is, they have a "useful life" that can be measured in hours......(pepsin has an average life od about 1 hour)....and so on....
I notice that some enzymes, cease to work on other Ph tht is not the "optimum" for obtaining the proper Pk,,,,(subzero values in trhe scale)......like pepsin when it reaches the duodenum...for example,,,,and most of the molecules of peptidases cease to act, in the colon (when they were very active in the mild alkaline environment of the ileon)....

Answer 2

The pH scale goes from 0-14. Anything below 7 is classified as acidic. pH 7 is neutral, and everything above 7 is alkaline. The stomach secretes Hydrochloric acid and may reach pH levels as low as 1- which is very acidic. Pepsin and other stomach proteases are adapted to normal enzymatic catalysis at these very acidic pH levels. Hope that answered your question.

Answer 3

some enzymes are designed to function in different pH or tempature ranges. Not all enzymes will function the same. If pepsin is supposed to work in an acidic enviroment wouldn't it be defeating the purpose if it worked in 7 pH. It would break down your stomach lining and cause an ulcer.

Answer 4

Every enzyme works at a certain pH. The only exception is papain, which works at a wide range of pH. Pepsin works best at pH 1-2. In fact, pepsin is inactivated at neutral pH. HCl concentration 0.1 N gives pH 1, 0.01 N gives pH 2, because pH = -log [H+]. The higher the H+ concentration, the lower the pH.

Answer 5

1 pH (low pH level) = high acidity /no alkalinity
14 pH (high pH level) = high alkalinity / no acidity.

pH is a scale 1 - 14 where 7 = neutral

and yes different enzymes function optimally at different pH ranges, but does not mean that they dont work at all in different ranges, just not as well as they should if they were in the right environment.

Answer 6

They will suck or do nothing at all. They are designed to work at certain a pH. Changes can add/remove electrons and disrupt binding of the substrate. Extreme pHs can denature the enzyme.

Answer 7

Actually some enzymes work best in acidic condition while others work best in alkaline medium. In fact HCl provides the optimum medium for pepsin to work.

Answer 8

1

Answer 9

the lower the pH, the more acidic it is

pH = -log [H+]
the higher the H+ concentration, the lower the pH value will be