2.5 - Enzymes

Catalysts – speed up reactions without being used up or changed by the reaction

A. Activation energy – amount of energy needed to get a reaction started

B. Catalysts work by lowering the activation energy

Enzymes – Biological catalysts A. Proteins – very specific shapes B. Usually end in –ase

C. Substrate – reactants in an enzyme- catalyzed reaction D C. Substrate – reactants in an enzyme- catalyzed reaction D. Active site – spot on enzyme where substrate binds ****Remember – VERY specific!!!***

How enzymes work A. Lower activation energy by positioning substrates in a way that is favorable to reacting 1. Substrate must enter active site with minimum rate of motion necessary for reaction to occur (enzyme provides NO energy!)

B. Substrate joins with enzyme at active site to form enzyme-substrate complex Product(s) released, enzyme unchanged and free to catalyze the reaction again with new set of reactants

Induced fit model – enzyme undergoes change in conformation as it interacts with substrate

Factors that affect enzyme activity A. Temperature 1. As temperature increases, molecules move faster, collide more often and with more energy

2. Enzymes have an ideal temperature a 2. Enzymes have an ideal temperature a. Too cold – molecular motion too slow b. Too hot – enzyme loses shape

pH - proportion of H+ and OH- ions 1. H+ and OH- ions can bind with enzyme or substrate and influence bonding between the two

Substrate Concentration 1. As substrate concentration increases, enzyme activity increases until a maximum rate is achieved

Inhibition A. Competitive Inhibition – a molecule binds into the active site, blocking access to the substrate 1. Can be reversible or irreversible 2. If reversible, can be overcome by increasing substrate concentration

Non-competitive Inhibitors – bind elsewhere on enzyme and forces change in shape of active site 1. Also called allosteric inhibition 2. Can be reversible or irreversible

End-Product Inhibition 1. Metabolic pathways – most metabolic functions in the body are actually a series of reactions 2. Final product acts as an allosteric inhibitor to the first enzyme in the series