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2.4 Chemical Reactions and Enzymes
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A Chemical Reaction is a process that changes one set of chemicals into another.
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The chemicals that get changed or enter into the reaction are known as the
Reactants.
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The products are the chemicals that produced by a chemical reaction.
Ex:
CO2 + H2O  H2CO3 (carbonic acid)
Reactants
Products
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Chemical reactions always involve the breaking of bonds in reactants and the forming of new
bonds in the products
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Energy is released or absorbed whenever bonds are formed or broken.
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If energy is released it is known as an Exothermic reaction
(Usually spontaneous 2H2 + O2 H2O heat)
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If energy is absorbed it is known as an Endothermic reaction.
(Need source of energy H2O Electric currentH2 + O2)
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Energy can be released in many forms such as light, heat and/or sound.
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Some chemical reactions require energy to get the reaction started. This is known as the
Activation energy. (fig 2-19 pg 50)
Enzymes
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Some chemical reactions are too slow or have activation energies that are too high to make them
practical for living tissue.
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A catalyst speeds up a chemical reaction by lowering the reactions activation energy
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Cells use a type of catalyst called an enzyme to speed up the chemical reactions that must take
place in living tissue.
The enzymes are not changed or used during chemical reactions.
What type of organic molecule is an enzyme? Protein
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Enzymes are very specific in the type of reaction they catalyze. Part of the enzymes name
usually comes from the Chemical reactions they catalyse (Ex – Lactase breakdown lactose)
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For a reaction to take place, the reactants must collide with enough energy (activation energy) to
break the existing bonds, or come into contact with an enzyme.
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In a reaction that is catalyzed by an enzyme the reactants are called the substrate
The place on the enzyme where the substrates bind is called the active site.
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Recall that proteins have a very specific shape.
The active site for each enzyme can only fit a specific type of substrate
. ** compared to a lock-and-key **(fig. 2-21 & 2-22 on pgs 52-53)
Enzyme
Substrate
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Active site
What are some things that may regulate the enzyme activity in the cells of your tissue?
_temp , pH, other proteins that have ability to turn the enzymes on & off