CH 2.4 Chemical Reactions & Enzymes

Everything that happens in an organism – growth…movement…reproduction… is based on chemical reactions.

Chemical reactions involve changes in the chemical bonds that join atoms in compounds.

… pretty important thing. Breathing, for example…

Your cells constantly produce carbon dioxide as a normal part of their activity. CO2 + H2O H2CO3 H2CO3 CO2 + H2O

Your cells constantly produce carbon dioxide as a normal part of their activity. As it enters the blood, CO2 reacts with water to form the highly soluble compound – carbonic acid. CO2 + H2O H2CO3 H2CO3 CO2 + H2O

Your cells constantly produce carbon dioxide as a normal part of their activity. As it enters the blood, CO2 reacts with water to form the highly soluble compound – carbonic acid. CO2 + H2O H2CO3 In your lungs, this reverse reaction produces CO2 gas – released when you exhale. H2CO3 CO2 + H2O

Energy is released or absorbed whenever chemical bonds form or are broken.

Because chemical reactions involve breaking & forming bonds, they involve changes in energy.

Reactions that release energy often occur spontaneously.

Reactions that absorb energy will not occur without an energy source.

2H2 + O2 2H2O

2H2O 2H2 + O2

To stay alive, organisms must carry out reactions that require energy. Every organism must have a source of energy to carry out chemical reactions.

Plants get that energy through photosynthesis.

Humans get that energy by eating plants and/or animals, then metabolizing (breaking down) that food via chemical reactions during digestion.

Activation Energy: the energy needed to start a chemical reaction.

Activation energy is a factor in whether the reaction releases or absorbs energy.

Energy absorbed Which is which??? Energy released

Some chemical reactions necessary for life are too slow, or have very high activation energies that make them impractical for living tissue. Catalysts speed up reactions by lowering the activation energy.

Enzymes are proteins that act as biological catalysts. Enzymes speed up the reactions that take place in cells.

CO2 + H2O H2CO3 …remember this reaction? Without the enzyme carbonic anhydrase to speed it up, CO2 would build up in your bloodstream and cause severe health issues!

Enzymes are affected by: • pH • temperature (your enzymes work best at 98.6⁰) Enzymes play essential roles in: • regulation of chemical pathways • making material needed by cells • releasing energy • transferring information