Enzyme Function and Factors Affecting Enzyme Activity

Posted on Jan 8, 2025 in Biology

Enzymes

Active site: The area or the pocket on the enzyme where the substrate binds.
Enzyme: Proteins that catalyze chemical reactions (increase the rate by lowering the activation energy).
Each enzyme catalyzes a specific reaction for a specific substrate.
Enzymes are not used up during the chemical reactions.
Enzymes are very specific because both the enzyme and the substrate possess specific complementary shapes that fit into one another.
The binding of the substrate to the enzyme causes the chemical bonds of the substrate to weaken.
This eventually causes the reactions that take place that form the products.
After the products are released, the enzyme can bind to another substrate because enzymes are not used up in these chemical reactions.

When a substrate comes close to the active site of the enzyme, it can collide and bind to the active site of the enzyme.
Since the substrate is dissolved in water around the enzyme, the substrates and enzymes are in continuous motion.
The direction and movement is constantly changing and is random.
Collisions occur at random between the substrate and enzyme.
Successful reactions only occur if the substrate and the active site of the enzyme are correctly aligned and collide with sufficient kinetic energy.

When heat is added to a liquid, the particles speed up, thus giving them more kinetic energy.
In a liquid that contains substrates and enzymes, the increase in kinetic energy will cause more collisions between substrates and enzymes, thereby increasing enzyme activity and reaction rates.
However, as temperature increases and becomes too high, the bonds of the enzyme begin to vibrate and eventually break.
This causes the enzyme to lose its 3D shape, including the shape of the active site.
When the enzyme loses its shape and can no longer catalyze reactions, the enzyme is said to be denatured.
When the enzymes in solution become denatured, the reaction rate decreases dramatically.
Enzyme denaturation is usually permanent.

The optimum rate of reaction is when the graph reaches the top of the curve, which is around 40ºC for most enzymes.

pH is dependent on the number of H+ ions compared to the number of OH- ions.
When a solution has a high number of H+ ions, the solution is said to have a low pH (acid). If a solution has a high number of OH- ions, the solution is said to have a high pH (base).
Enzymes have an optimum pH at which they work the best.
When deviations occur away from this optimum pH, the enzyme’s activity or reaction rate decreases.
When the pH moves too far away from the enzyme’s optimum pH, the enzyme will lose its shape and denature, drastically decreasing enzyme activity.
For example, the optimum pH for the enzyme pepsin is around 2-3. If the pH increases to 5 or 6, the enzyme loses its ability to catalyze reactions (breakdown of proteins in the stomach).
Most enzymes have an optimum pH close to neutral (7).

With a fixed amount of enzymes, as substrate concentration increases, the rate of reaction will increase because more collisions between enzymes and substrates will occur.
However, as substrate level increases, more and more enzyme active sites are being filled.
At a certain substrate concentration, all active sites on the enzymes are being used or are filled.
At this point, the reaction rate levels off and remains constant.
Adding more substrate to the reaction will not increase the reaction rate. Reaction rate can only be increased with the addition of more enzymes.