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Process in which one or more substances, the reactants, are converted to one or more different substances.Many reactions occur in living things, like breaking down food, cellular respiration, and photosynthesis. These reactions often time use enzymes to occur.

What is a Chemical Reaction?

Catalyst- something that speeds up a reaction

Proteins or RNA segments that speed up the rate of a chemical reaction in a living organism.They build some substances and break others down. All living things have enzymes. Our bodies naturally produce enzymes.

What is An Enzyme?

Activation energy is the minimum amount of energy needed to start a chemical reaction. The minimum amount of additional energy needed by a reacting molecule to get transformed into the product is termed activation energy.

Enzymes Lower Activation Energy

Enzymes work by binding to reactant molecules and holding them in such a way that the chemical bond-breaking and bond-forming processes take place more readily.

Parts of an Enzyme

Enzymes have an active site which is where the substrate molecules bind to the enzyme. Enzymes are highly specific and each type of enzyme will only bind to certain substrates. This is due to their unique 3D shape created by their level of structure. We say the substrate is complemenatry in shape.
Enzyme Active Sites

When do Enzymes Work Best?

Each enzyme has ideal conditions in which it works best.

Factors That Affect Enzymes

When the temperature or pH gets too high, it can denature the enzyme.That means it changes the shape of the active site so substrates can't fit.This will either slow down or stop the reactionfrom occuring.

Enzymes Denature

A base is a solution that has a lower concentration of hydrogen ions than pure water. It does this by providing hydroxide ions (OH-) or another ion or molecule. This then removes H+ ions from the solution. It has a pH of 8-14

An acid is a solution that has a higher concentration of hydrogen ions than pure water. It does this by donating one of its hydrogen atoms through dissociation - i.e. putting more H+ ions into the solution. It has a pH of 0-6


The pH scale is a way of ranking how acidic or alkaline a substance is. It goes from 0 - 14.

Let's review what pH is.

Enzymes: pH

EOC Question Examples

EOC Question Examples