Enzymes catalyze chemical reactions by lowering activation energy barriers and converting substrate molecules to products.
Enzymes bind with chemical reactants called substrates. A specific chemical substrate matches this site like a jigsaw puzzle piece and makes the enzyme specific to its substrate.
Environmental conditions can affect an enzyme’s active site and, therefore, the rate at which a chemical reaction can proceed. Increasing the environmental temperature generally increases reaction rates because the molecules are moving more quickly and are more likely to come into contact with each other. However, increasing or decreasing the temperature outside of an optimal range can affect chemical bonds within the enzyme and change its shape. If the enzyme changes shape, the active site may no longer bind to the appropriate substrate and the rate of reaction will decrease. Dramatic changes to the temperature and pH will eventually cause enzymes to denature.
When an enzyme binds its substrate, it forms an enzyme-substrate complex. This complex lowers the activation energy of the reaction and promotes its rapid progression by providing certain ions or chemical groups that actually form covalent bonds with molecules as a necessary step of the reaction process. Enzymes also promote chemical reactions by bringing substrates together in an optimal orientation, lining up the atoms and bonds of one molecule with the atoms and bonds of the other molecule. This can contort the substrate molecules and facilitate bond-breaking. The active site of an enzyme also creates an ideal environment, such as a slightly acidic or non-polar environment, for the reaction to occur. The enzyme will always return to its original state at the completion of the reaction. One of the important properties of enzymes is that they remain ultimately unchanged by the reactions they catalyze. After an enzyme is done catalyzing a reaction, it releases its products (substrates).
Practice Questions
Khan Academy
MCAT Questions
Practice Exam 1 C/P Section Question 12
Official Guide B/B Section Question 25
Key Points
• The enzyme’s active site binds to the substrate.
• When an enzyme binds its substrate it forms an enzyme-substrate complex.
• The activation energy reacquired to start a reaction is reduced by the enzymes.
• Enzymes promote chemical reactions by bringing substrates together in an optimal orientation, thus creating an ideal chemical environment for the reaction to occur.
• The enzyme will always return to its original state at the completion of the reaction.
Key Terms
substrate: A reactant in a chemical reaction is called a substrate when acted upon by an enzyme.
induced fit: Proposes that the initial interaction between enzyme and substrate is relatively weak, but that these weak interactions rapidly induce conformational changes in the enzyme that strengthen binding.
active site: The active site is the part of an enzyme to which substrates bind and where a reaction is catalyzed.
catalyze: accelerate or speed up
