This presentation includes the following: Chemical Reactions Energy in Reactions Enzymes Enzyme Action

Chemical Reactions Chemical Reaction: Reactants: Products: A process that changes one set of chemicals into another set of chemicals Reactants: Elements entered into the reaction Products: Elements or Compounds produced by the reaction Always involves the breaking of bonds in reactants and forming of new bonds in products. REACTANTS PRODUCTS

Chemical reactions Existing bonds are broken and new bonds are formed Requires exchange of energy between molecules and environment Reactant molecules absorb energy for their bonds to break Energy is released when bonds of product are formed

Example of a chemical reaction: Carbon Dioxide in your Blood Your cells produce carbon dioxide as waste Carried to your lungs via the bloodstream Carbon dioxide isn’t very soluble in water As it enters the blood, it reacts with water Carbon dioxide plus water produces a soluble compound called carbonic acid and is carried through the blood CO2 + H2O H2CO3 In the lungs the reaction is reversed H2CO3 CO2 + H2O You exhale and get rid of the carbon dioxide gas!

Energy in Reactions: Energy is either released or absorbed in chemical reactions…Why? Because bonds are formed or broken! Exothermic reactions Reactions that release energy Often occur spontaneously EX: Hydrogen gas burning + oxygen water vapor Endothermic reactions Absorb energy Will not occur without a source of energy EX: Water hydrogen + oxygen gas

What does energy have to do with anything? Organisms have to carry out reactions that require energy in order to stay alive THUS: every organism needs a source of energy to carry out chemical reactions Even exothermic reactions (releasing energy) do not always occur spontaneously This is a good thing  They need energy to get started

Activation energy The energy needed to get a reaction started is called…Activation Energy  The energy required to break bond in the reactants

Some chemical reactions are too slow Some have an activation energy that is too high BUT…your body has solved these dilemmas by using catalysts

Enzymes Proteins that act as biological catalysts. Catalyst: Enzymes: A substance that speeds up the rate of chemical reactions. It lowers the activation energy required for the reaction to occur. Enzymes: Proteins that act as biological catalysts. Cells use enzymes to speed up chemical reactions that take place in the cell.

Please open your books to page 51 Figure 2-20 With the person sitting next to you… Describe the reaction if enzymes were NOT present. Would a reaction take a longer time or a shorter time with an enzyme?

Answers Without an enzyme, the reaction would need more activation energy With an enzyme, the reaction would take a shorter amount of time

Enzymes Basically: Enzymes make reactions that would occur eventually in the cell anyway happen faster This lets the cell have a dynamic metabolism

Enzyme Action: For a chemical reaction to take place, the reactants must collide with enough energy so that the existing bonds will be broken and new bonds will be formed in the product.

Enzyme-Substrate Complex: Enzymes provide a site where reactants can be brought together to react. The reactants are known as substrates.

Enzymes-Substrate Complex The enzyme binds to its substrate The catalytic action of the enzyme converts the substrate to the product Enzymes usually end in “-ase” enzyme SUBSTRATE(S) PRODUCT(S)

Please turn to page 52 With the person sitting next to you… Define “active site” Describe the relationship between a substrate and the active site What holds the enzyme and the substrate together?

Remember… Enzymes provide a site where substrates can be brought together to react. Such a site reduces the energy needed for a reaction The active site is where the substrate binds to the enzyme Each enzyme (protein) has a specific shape Each substrate has a complementary shape The fit is like a lock and key The enzyme remains unchanged!

Regulation of Enzyme Activity Enzymes can be affected by: pH Temperature Enzymes can be either “on” or “off” pH

Regulation of Enzyme Activity: Temperature What group of organic compounds do enzymes belong to? Proteins! Proteins (thus enzymes) are temperature sensitive

Regulation of Enzyme Activity: Temperature Up to a point, an increase in temperature is beneficial for the enzyme Remember—temperature increase causes molecules to move faster Thus more substrates are being brought to the active site of the enzyme Each enzyme has conditions that it likes to function in What do you think is the optimal temperature for enzymes in your body?

Regulation of Enzyme Activity: Temperature A change in the optimal temperature can cause a protein to lose its shape This is called “denaturing” When an enzymes denatures, it loses its shape and cannot function properly anymore

Regulation of Enzyme Activity: pH Just as each enzyme has an optimal temperature, an optimal pH exists as well Usually pH of 6-8 Exceptions Pepsin (digestive enzyme in your stomach) functions best at pH 2 It is adapted to the conditions of your stomach!