Biomolecules Enzymes

Chemical Reactions Process that changes one set of chemicals into another Example: Carbon dioxide and water form carbonic acid CO2 + H2O → H2CO3 Reactants – elements or compounds that you start with, found on the left hand side of the reaction arrow. Products – elements or compounds produced from the reactants, found on the right hand side of the reaction arrow. Chemical reactions involve the breaking of bonds in the reactants and the formation of new bonds in the products

Energy in Chemical Reactions Energy can be released or absorbed in chemical reactions. Chemical reactions require some initial input of energy in order to start the reaction; this is called the activation energy. Activation Energy

Enzymes A group of proteins that act as catalysts A catalyst is a substance that speeds up the rate of a chemical reaction Enzymes are not used up during the reaction, so once they catalyze the reaction, they can be used again and again Unchanged Enzyme

Activation Energy Enzymes catalyze reactions by decreasing the activation energy, the amount of energy needed to start a reaction. The energy released is the same whether the reaction is catalyzed by an enzyme or not.

Enzyme-Substrate Complex The substance that binds to the enzyme is called the substrate The enzyme and substrate must have complementary shapes in order to bind The location on the enzyme where the substrate binds is called the active site. The enzyme-substrate complex is like a lock and key mechanism. Substrate Enzyme

Enzyme-Substrate Complex (cont.) A lock will only accept one key just as an enzyme will only accept a specific substrate. If the substrates do not fit in the activation site then the reaction will not take place. Each enzyme is very specific. There are usually only one or two molecules that will fit the active sites exactly.

Enzyme Action Enzymes can catalyze reactions that break down the substrate (catabolic) or join two substrates together (anabolic)

Factors that Affect the Rate of Enzyme Activity Temperature pH Concentration of Substrate or Enzyme

Temperature Each enzyme has an optimal temperature range. If the temperature is too low, the enzyme works slowly. If the temperature is too high, the enzyme may break down (denature) and not work.

pH Each enzyme has an optimal pH range. If the pH is too low (acidic), the enzyme usually denatures. Some enzymes work best in acidic environments (i.e. stomach enzymes).

Concentration of Substrate or Enzyme The more enzyme that is available, the faster the reaction tends to go, if there is excess substrate The more substrate available, the faster the reaction tends to go, until the enzyme is saturated

Competitive Inhibitor Substances that bind to the active sites of enzymes but are not the substrate are known as competitive inhibitors because they compete with the substrate for the active site

Non-Competitive Inhibitor Substances that bind to enzymes at a site other than the active site are called non-competitive inhibitors When non-competitive inhibitors bind to the enzyme, the enzyme changes shape so the substrate can no longer bind to the active site