Energy,

Chemical Reactions,

and

Enzymes

Energy• the ability to move or change matter

– found in many forms

– can be converted from one form into another

Chemical Reactions• process that changes one set of

chemicals into another

• always involves changes in the chemical bonds that join the atoms in the compounds

Chemical Reactions• reactants

– substances that enter into a chemical reaction 

– found on the left side of the arrow• products

– substances produced by the chemical reaction

– found on the right side of the arrow

H2CO3H2OCO2+

carbon dioxide plus water forms carbonic acid

Energy in Reactions• some chemical reactions release

energy and others absorb energy

• energy changes are an important factor in determining whether a reaction will occur

Exothermic• chemical reaction that releases energy

– C → A + B + Energy

Endothermic• chemical reaction that needs to absorb

energy to begin– A + B + Energy → C

Energy in Reactions• Label each of the following

reactions as either:

– Energy-Releasing Reaction

or

– Energy-Absorbing Reaction

(from Holt Biology, pg. 39)

Use the location of the REACTANTS and PRODUCTS to help.

Energy in Reactions

Energy in Reactions

Activation Energy• energy needed to start a chemical

reaction– ex: spark plug in an engine

Enzymes• enzymes are biological catalysts

– catalyst• substances that reduce the activation energy of

a chemical reaction• reducing activation energy allows the reaction

to occur more frequently and faster

Hydrolysis of Sucrose by SucraseMcGraw - Hill

Enzymes & Activation Energy

Reaction pathwaywithout enzyme

Activation energywithout enzyme

Activationenergywith enzymeReaction pathway

with enzyme

Reactants

Products

What type of macromolecule are most enzymes?

• enzymes are proteins• these proteins enzymes increase the

speed of chemical reactions– some enzymes break molecules apart

What type of macromolecule are most enzymes?

• enzymes are proteins• these proteins enzymes increase the

speed of chemical reactions– some enzymes break molecules apart– other enzymes put molecules together

What type of macromoleculeare enzymes?

• enzymes are proteins• these proteins enzymes increase the

speed of chemical reactions– some enzymes break molecules apart– other enzymes put molecules together– do not get used up in a chemical reaction

• help maintain homeostasis

Substrate

• substance on which an enzyme acts during a chemical reaction

• substrate = reactants

Active Site• the location on an enzyme that attaches to a

substrate

How Enzymes WorkMcGraw - Hill

Enzyme Specificity• enzymes are specific because only its substrate

fits into its active site– enzymes are similar to a lock and key

Enzyme Efficiency• work well only within a certain set of conditions

– changes in conditions like pH and temperature can change the shape of the protein

– when the substrate no longer fits the active site, the enzyme will not work• the “lock and key” no longer fit in one another

Example• lactase is an enzyme that breaks down milk

sugar (lactose) lactase

lactose glucose + galactose

Why is lactase written above the arrow and not included in the chemical equation?

• because enzymes (like lactase) are not used up in chemical reactions– they can be re-used over and over again for the same type

of reaction

lactaselactose glucose + galactose