1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that
occur in specialized areas of the organism’s cells. As a basis for understanding this concept:
1. b. Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction
equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the
surroundings.
Almost all enzymes are protein catalysts made by living organisms. Enzymes speed up favorable (spontaneous)
reactions by reducing the activation energy required for the reaction, but they are not consumed in the reactions
they promote.
Notes:
Enzymes are proteins that act as catalysts in the cell that speed up reactions that otherwise would occur too slowly
for life to be possible. Enzymes do not make impossible reactions occur, they simply speed up natural ones. The
enzyme function by reducing the activation energy, the energy needed to start a chemical reaction. The chief
advantage of enzymes in living systems is that they allow the chemical reactions of the body to occur at relatively
low temperatures. Since enzyme molecules do NOT become permanently attached to substrate molecules, they
may later become free too catalyze other molecules in their reactions. For this reason, enzymes are effective in small
amounts.
The molecule that the enzyme works on is called the substrate. Together with the enzyme it is referred to as the
enzyme substrate complex.
All enzymes have a three-dimensional structure. Their shape is due to the twisting and folding of the molecule.
Their function is due to their shape. Anything that changes the shape will affect the enzyme. Temperature,
chemicals, and pH changes may inactivate (denature) enzymes by breaking hydrogen bonds and changing the shape
of the enzyme. The chemical makeup may not change, but if the structure changes, the enzyme will not function
properly. This will affect the rate of reaction.
Some Factors Influencing Enzyme Activity
1. pH (around neutral is best for most enzymes)
2. Temperature (increasing temp. to about 37 C. increases enzyme function -- above 60 C, the denaturing of many
enzymes occurs) Denaturing is the changing the shape of the enzyme (protein) structure so that it loses all ability to
function
3. As enzyme concentration increases with a specific amount of substrate the rate of reaction will first increase and
then level off.
4. As substrate concentration increases with a specific amount of enzyme, the rate of reaction will first increase and
then level off.
Often enzymes are associated with coenzymes. Coenzymes are an additional nonprotein substance held to the
enzyme by ionic or hydrogen bonding. These can be vitamins, minerals, etc. Coenzymes are neither used up
nor altered by their participation in a chemical reaction.