A scientist observes that, when the pH of the environment surrounding an enzyme is changed, the rate the enzyme catalyzes a reaction greatly decreases. Which statement best describes how a change in pH can affect an enzyme?

A. A pH change can cause the enzyme to change its shape.
B. A pH change can remove energy necessary to activate an enzyme.
C. A pH change can add new molecules to the structure of the enzyme.
D. A pH change can cause an enzyme to react with a different substrate.

A- A pH change can cause the enzyme to change its shape

Explanation:

A rise or fall in the pH of the medium from the optimum of pH 7 usually affect  the  enzymes' active sites  of  and therefore the  shape and  the  rate of enzyme activity.

Assuming  the pH is too low, the enzyme medium becomes acidic;Acidosis. The high Hydrogen ions concentration  interacts with the R-groups of the amino acids moiety of the enzymes, this interaction affects the ionization of the  R-groups, disrupting the ionic bonding holding these R-groups in shape.

This results in loss of the 3-Dimensional shape arrangements of the protein molecule  and therefore of the active sites. Since active sites of  enzymes  determines the specificity of the enzymes substrate- complex to give enzyme-product complex, the catalytic activity of the enzymes decreases, the rate of  reaction decreases,and products formation stops, and the reaction also stops.

The same is applicable to extremely high pH=Alkalosis.

However, the effective buffer system of the body prevents this scenarios from happening in real sense in the body. Through mopping by the  haemoglobin, excretion by the kidney, etc

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