2.4 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 Reactions

• Reaction in which heat is given off (Ex. 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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Catalyst

• A substance that speeds up the rate of a reaction

• It works by lowering activation energy

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Enzymes

• Proteins that act as biological catalysts

• They speed up chemical reactions that take place in cells

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

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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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http://www.youtube.com/watch?v=CZD5xsOKres

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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