NOTES: 2.4 – Chemical Reactions and Enzymes

CHEMICAL REACTIONS ● Living things are made up of chemical compounds – some simple, some complex ● plus…EVERYTHING that happens in a living organism (growth, reproduction, movement, response to stimulus, etc.) is based on CHEMICAL REACTIONS!

CHEMICAL REACTIONS ● a chemical reaction is a process that changes one set of chemicals into another ● REACTANTS: the substances that enter into a chemical reaction ● PRODUCTS: the substances produced by a chemical reaction ● EX: CO2 + H2O  H2CO3

Energy in Reactions: ● some chemical reactions release energy, and other reactions absorb it ● living organisms carry out many reactions that require, or absorb, energy ● this means every organism must have a source of energy ● HOW do living things obtain energy?...

Energy in Reactions: ● PLANTS can trap energy from sunlight & store it in energy-rich organic compounds ● ANIMALS get their energy when they consume plants or other animals ● humans (& other animals) release the energy needed to grow, think, dream…through the chemical reactions that occur when we metabolize digested food

Activation Energy: ● most reactions require an initial burst of energy to get them going… ● ACTIVATION ENERGY: the energy that is needed to get a reaction started ● example: paper will burn vigorously, but only after it is lit with a match or spark first..the lit match provides the activation energy!

Enzymes as Biological Catalysts ● What is a catalyst? ● a CATALYST is a substance that speeds up the rate of a chemical reaction ● catalysts work by lowering a reaction’s activation energy ● many reactions critical to life are too slow to make them practical for living cells…unless we speed them up with CATLYSTS…(ENZYMES!)

ENZYMES! ● ENZYMES speed up chemical reactions that take place in cells… ● they work by lowering the activation energy of a reaction ● EX: CO2 + H2O  H2CO3 ● the reaction above removes CO2 from our blood…without the enzyme that speeds it up, CO2 would build up in the body & cause damage

PROTEINS WORKING AS ENZYMES ● are proteins ● control / regulate the speed of reactions (often they increase the speed of reactions)

ENZYMES: ● are not changed or “used up” by a reaction; can be used over and over

● each enzyme is specific to a SUBSTRATE ● SUBSTRATE = the substance the enzyme acts on   Substrate ==> enzyme-sub.==> product + complex + enzyme enzyme

● ACTIVE SITE = region of an enzyme which binds to the substrate is usually a pocket or groove on surface compatible “fit” between shape of enzyme’s active site and shape of substrate “Lock and Key” analogy

Factors Affecting Enzyme Activity 1) Temperature: -as temp increases, reaction rate increases -BUT, if temp gets too high, enzyme denatures and loses its shape and function -optimal range for human enzymes: 35-40°C (human body temp is 37°C)

2) pH: -optimal range for most human enzymes: pH 6-8 *some enzymes operate best at extremes of pH (e.g. the digestive enzyme PEPSIN, found in the acidic environment of the stomach, works best at pH 2)

3) Regulatory molecules: -most enzymes are regulated by the presence of other molecules in the cell -these “regulatory” molecules act as chemical signals that can switch an enzyme “on” or “off” as needed