Environmental factors Flashcards
The pH at which an enzyme functions optimally is called the
pH optimum
Making the solution more basic or more acidic sharply
decreases the rate of the reaction
These pH changes alter the degree of ____ of amino acid R groups in the protein, as well as the extent to which they can ______
ionization
H bond
This causes the enzyme to lose its biologically active configuration; it becomes ____. Less drastic changes in the R groups of an enzyme active site can also destroy the ability to form the ___________
denatured
enzyme-substrate complex.
Some environments within the body must function at a pH far from
7
For instance, the pH of the stomach is approximately
2
why is the pH of the stomach 2
as a result of the secretion of hydrochloric acid by cells of the stomach lining.
The proteolytic digestive enzyme ____ must effectively degrade proteins at this extreme pH
pepsin
In the case of pepsin, the enzyme has evolved an amino acid sequence that can maintain a ___ tertiary structure at pH ___ and is most active in the hydrolysis of peptides that have been denatured by very low pH. Thus, pepsin has a pH optimum of __.
stable
2
2
functions under the conditions of higher pH found in the intestine
trypsin
Both pepsin and trypsin cleave peptide bonds by virtually identical mechanisms, yet their amino acid sequences have evolved so that they are stable and active in______ environments.
very different
The body has used the adaptation of enzymes to different environments to protect itself against one of its
own destructive defense mechanisms
Within the cytoplasm of a cell are organelles called ____. “suicide bags” because they are membrane-bound vesicles containing about fifty different kinds of ____ that degrade large biological molecules into small molecules.
lysosomes
hydrolases
If the hydrolytic enzymes of the lysosome were accidentally released into the cytoplasm of the cell, the result would be the
destruction of cellular macromolecules and death of the cell
Because of this danger, the cell invests a great deal of energy in maintaining the integrity of the
lysosomal membrane
An additional protective mechanism relies on the fact that lysosomal enzymes function optimally at an acid pH
4.8
Should some of these enzymes leak out of the lysosome or should a lysosome accidentally rupture, the cytoplasmic pH of ________
7-7.3
renders then inactive
The enzymes in our cells are rapidly destroyed if the temperature of their environment rises much above ___ but they remain stable at much ____ temperatures
37 C
lower
This is why enzymes used for clinical assays are stored in
refrigerators or freezers before use
The rate of the uncatalyzed reaction steadily increases with _____ temperature because ____collisions occur with sufficient ____ to overcome the energy barrier for the reaction.
increasing
more
energy
The rate of an enzyme-catalyzed reaction also increases with modest increases in temperature because there are increasing numbers of collisions between the ____ and the ____.
enzyme
substrate
the enzyme is functioning optimally and the rate of the reaction is maximal.
temperature optimum
above the temperature optimum, increasing temperature begins to increase the _____ energy of the bonds within the enzyme. Eventually, so many bonds and weak interactions are _____that the enzyme becomes _____, and the reaction _____
vibrational
disrupted
denatured
stops
because heating enzymes and other proteins destroys their three-dimensional structure, and hence their activity, a cell cannot survive
very high temperatures
