2.4 Notes

Living things are made up of chemical compounds but chemistry isn't just what life is made of - chemistry is also what life DOES.

Chemical Reactions

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

A chemical reaction is a process that changes, or transforms, one set of chemical into another by changing the chemical bonds that join atoms in compounds.

Mass and energy are conserved during transformations, including chemical reactions that occur in living organisms.

EACH REACTION HAS

• Reactants: the elements or compounds that ENTER into a chemical reaction.
• Products: the elements or compounds PRODUCED by a chemical reaction.

ENERGY CHANGES

Energy is released or absorbed whenever chemical bonds are formed or broken during chemical reactions.

Energy is released in the form of heat, and sometimes when hydrogen gas explodes - light and sound.

Every organism must have a source of energy to carry out the chemical reactions it needs to stay alive.

ENERGY SOURCE

Every organism must have a source of energy to carry out the chemical reactions it needs to stay alive.

The energy that is needed to get a reaction started is called its activation energy.

ENZYMES

Enzymes speed up chemical reactions that take place in cells.

Temperature, pH, and regulatory molecules affect the activity of enzymes.

A catalyst is a substance that speeds up the rate of a chemical reaction by lowering the reaction's activation energy

Enzymes are proteins that act as biological catalysts.

Enzymes act by lowering the activation energies, which has a dramatic effect on how quickly the reactions are completed.

Enzymes are very specific, generally catalyzing only one chemical reaction.

ENZYME-SUBSTRATE COMPLEX

For a chemical reaction to take place, the existing bonds will be broken and new bonds will be formed.

Enzymes provide a site where reactants can be brought together to react. Such a site reduces the energy needed for a reaction.

Remember the reactant is also known as a substrate in reactions that have enzymes.

The substrates bind to a site on the enzyme called the active site.

The active site and the substrates have complementary shapes.

The active site and substrate fit together so precise that they are often compared to a lock and key.

Enzymes produced by human cells generally work best at temperatures close to 37*C, the normal temperature of the human body.

Enzymes work best at certain pH values, for example, the stomach enzyme pepsin, which begins protein digestion, works best under acidic condions.

Chemical signals within cells are able to switch enzymes "on" or "off" as needed.