What effect will boiling have on an enzyme's activity?
The enzyme will no longer function.
An enzyme is a protein molecule with a fixed 3-dimensional shape that is held in place by ionic bonds, hydrogen bonds and such. However, due to boiling these bonds will be broken and tertiary structure of the enzyme will be lost and it will not be able to form an enzyme-substrate complex to form products. The active site will lose its complementary shape and the enzyme will be denatured. However, some enzymes are resistant to very high temperatures.