2 Enzymes Catalysts for biological reactions Most are proteins Lower the activation energyIncrease the rate of reactionActivity lost if denaturedMay be simple proteinsMay contain cofactors such as metal ions or organic (vitamins)
3 Flow of energy through life Life is built on chemical reactions
4 Chemical reactions of life Processes of lifebuilding moleculessynthesisbreaking down moleculesdigestion++
5 Nothing works without enzymes! How important are enzymes?all chemical reactions in living organisms require enzymes to workbuilding moleculessynthesis enzymesbreaking down moleculesdigestive enzymesenzymes speed up reactions“catalysts”enzyme+enzymeWe can’t live without enzymes!+
6 CATALYST – A SUBSTANCE THAT CAUSES A CHEMICAL REACTION TO HAPPEN MORE QUICKLY. Enzymes work by weakening bonds which lowers activation energy
7 Progress of the reaction Free energy of activation EnzymesWithout EnzymeWith EnzymeFreeEnergyProgress of the reactionReactantsProductsFree energy of activation
8 Enzymes are proteinsEach enzyme is the specific helper to a specific reactioneach enzyme needs to be the right shape for the jobenzymes are named for the reaction they helpsucrase breaks down sucroseproteases breakdown proteinslipases breakdown lipidsDNA polymerase builds DNA
9 Enzymes aren’t used up Enzymes are not changed by the reaction used only temporarilyre-used again for the same reaction with other moleculesvery little enzyme needed to help in many reactionssubstrateproductactive siteenzyme
10 Enzyme vocabulary Enzyme Substrate Products Active site helper protein molecule; catalystSubstratemolecule that enzymes work onProductswhat the enzyme helps produce from the reactionActive sitepart of enzyme that substrate molecule fits into
11 It’s shape that matters! Lock & Key modelshape of protein allows enzyme & substrate to fitspecific enzyme for each specific reaction
14 Enzyme Action: Induced Fit Model Enzyme structure flexible, not rigidEnzyme and active site adjust shape to bind substrateIncreases range of substrate specificityShape changes also improve catalysis during reaction
15 Enzyme Action: Induced Fit Model E S ES complex E PPSSSP
16 Factors Affecting Enzyme Action: Temperature Little activity at low temperatureRate increases with temperatureMost active at optimum temperatures (usually 37°C in humans)Activity lost with denaturation at high temperatures
18 What affects enzyme action Correct protein structurecorrect order of amino acidswhy? enzyme has to be right shapeTemperaturepH (acids & bases)
19 Order of amino acids Wrong order = wrong shape = can’t do its job! DNA folded proteinchain of amino acidsDNAright shape!folded proteinchain of amino acidsDNAwrong shape!
20 Factors Affecting Enzyme Action: Substrate Concentration Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant)Maximum activity reached when all of enzyme combines with substrate
21 Factors Affecting Enzyme Action Maximum activityReactionRatesubstrate concentration
22 Temperature Effect on rates of enzyme activity Optimum temperature greatest number of collisions between enzyme & substratehuman enzymes35°- 40°C (body temp = 37°C)Raise temperature (boiling)denature protein = unfold = lose shapeLower temperature T°molecules move slowerfewer collisions between enzyme & substrate
24 How do cold-blooded creatures do it? Enzymes work within narrow temperature ranges. Ectotherms, like snakes, do not use their metabolism extensively to regulate body temperature. Their body temperature is significantly influenced by environmental temperature. Desert reptiles can experience body temperature fluctuations of ~40°C (that’s a ~100°F span!).What mechanism has evolved to allow their metabolic pathways to continue to function across that wide temperature span?
25 pH Effect on rates of enzyme activity changes in pH changes protein shapemost human enzymes = pH 6-8depends on where in bodypepsin (stomach) = pH 3trypsin (small intestines) = pH 8
27 Enzyme Inhibition Inhibitors cause a loss of catalytic activity Change the protein structure of an enzymeMay be competitive or noncompetitiveSome effects are irreversible
28 Competitive Inhibition A competitive inhibitorHas a structure similar to substrateOccupies active siteCompetes with substrate for active siteHas effect reversed by increasing substrate concentration
29 Noncompetitive Inhibition A noncompetitive inhibitorDoes not have a structure like substrateBinds to the enzyme but not active siteChanges the shape of enzyme and active siteSubstrate cannot fit altered active siteNo reaction occursEffect is not reversed by adding substrate
31 Allosteric Site – undergoing a change in the shape and activity of a protein (as an enzyme) that results from the combination with another substance at a point other than the chemically active site.