Chemical Reactions and Enzymes

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Chemical Reactions• A process that changes or transforms one

set of chemicals into another

• Mass and energy are conserved

• Reactants Products

• 2 kinds: energy releasing (exothermic) and energy absorbing (endothermic)

Exothermic ReactionsReaction in which heat is given off (combustion of fuels)

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Endothermic Reactions• Reaction in which heat is absorbed (Ex.

water is evaporated)

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Activation Energy• Energy

needed to get a reaction going

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Six Types of Chemical Reaction

• 1) Combustion: when oxygen combines with another compound to form water and carbon dioxide (exothermic) meaning they produce heat.

• C8H20 + 13 O2 ---> 8 CO2 + 10 H2O

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• 2) Synthesis: when two or more simple compounds combine to form new one:

• A + B ---> AB

• One example: iron and oxygen to form iron (II) oxide: Fe + O ---> FeO

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• 3) Decomposition: a complex molecule breaks down to make simpler ones:

AB ---> A + B

• One example: electrolysis of water to make oxygen and hydrogen gas: 2 H2O ---> 2 H2 + O2

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• 4) Single displacement: This is when one element trades places with another element in a compound:

A + BC ---> AC + B

• One example: magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:

Mg + 2 H2O ---> Mg(OH)2 + H2

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• 5) Double displacement: when two different molecules switch places, forming two entirely different compounds: AB + CD ---> AD + CB

• One example: Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3

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• 6) Acid-base: The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water and salt: HA + BOH ---> H2O + BA (salt)

• One example of an acid-base reaction is the reaction of hydrochloric acid (HCl) with sodium hydroxide: HCl + NaOH ---> NaCl + H2O

• Acid often = HF, HCl, HBr, etc. H (hydrogen in front of elements in group 7 or something with oxygen.

• Base often = OH at the end of the compound. LiOH, NaOH, KOH, Mg(OH)2, Ca(OH)2.

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Photosynthesis

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Enzymes• Proteins that act as biological catalysts

• They speed up chemical reactions that take place in cells (catalysts)

• They are very specific and usually catalyze only one chemical reaction

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Catalyst

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• A substance that speeds up the reaction

• by lowering activation energy

Substrates• The reactants of enzyme-catalyzed

reactions• They bind to sites on the enzyme called

active sites Lock and Key

• CO2 + H2O H2CO3

substrate

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Regulation of Enzyme Activity

• Temperature, pH, and regulatory molecules can affect how well enzymes work

• Pepsin works best under acidic conditions (begins protein digestion)

• Some are regulated by molecules that carry chemical signals within cells that turn enzymes “on” or “off”

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