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Globular proteins that catalyze nearly all the chemical reactions in living things.


Why are they essential to life

Because they allow chemical reactions to occur rapidly and efficiently without having to increase the temperature of the system.



a reactant acted on by an enzyme


The activity of an enzyme depends on what

its 3D shape: tertiary structure


The shape of the enzyme is denatured

it no longer has its catalyzing ability


Equation of an enzyme catalyzing a reaction

Enzyme + substrate Enzyme-subsstrate------>enzyme + product


Why do some plants and vegetables turn burn when peeled or sliced

Due to a formation of a class of compounds called quinones by damaged plant cells


One function of quinones

protect the interior of the potato from invasion by soil microorganisms. Th brown patch not only seals the damaged area but is toxic to most microbes.


If large amounts of quinone is toxic to the plant how does the plant survive.

In addition to cellulose, the cell walls of potatoes contain catechol



Is a chemical when exposed to oxygen converts to quinone. However this process happens too slowly to be of any use to the damaged potato


The mechanisms that allow catechol to become quinone faster

The cytoplasm of potato cells contains a enzyme ( polyphenol oxidase or PPO) that speeds up the conversion.
In an undamaged potato the PPO remains inside the cell in the cytoplasm and the catechol is outside. When the cell is damaged the cytoplasm leaks out allowing the PPO to come into contact with the catechol and catalyze the conversion to quinone


The equation of the conversion to quinone

Enzyme (PPO) +substrate (CATECHOL) (enzyme-substate)---> enzyme( PPO)+ product(QUINONE) (brown color)


The activity of any enzyme can be measured by

detecting the product of the reaction catalyzed by the enzyme.


When a yellow/ brown color is seen what does it mean

that a reaction has occurred


the color f a quinone molecule is

a faint copper color, however, the intensity of the color is proportional to its concentration ( the darker the solution the more product present