CHAPTER 6 METABOLISM AND ENZYMES

LIFE IS FULL OF CHEMICAL REACTIONS Chemical reactions Reactants – what you start with Products – what you end with! Reactants that are acted upon by an enzyme are called substrates

WHAT IS AN ENZYME? Enzyme = molecules that make chemical reactions faster than they would be on their own (organic catalyst) - most are proteins, some are RNA - most are not used up in a reaction – they can be used again and again -common ending = -ase

HOW DO ENZYMES WORK Proteins (polypeptide chains) are folded into a 3D shape and have one or more active site Active sites = pockets where substrates bind to a protein and the reaction occurs

WHAT FACTORS INFLUENCE THE RATE ENZYMES WORK? Toothpickase Lab -Do all trials without the person looking. -All members must have their own graphs. -You may choose to complete your questions (complete sentences) as a group or as individuals (turn in 3 graph papers and 1 or 3 question sheets)

ENZYME FUNCTION In the liver, alcohol dehydrogenase helps break down toxic alcohols, but at the expense of liver function and energy metabolism

REACTIONS REQUIRE OR RELEASE ENERGY -We can predict whether a reaction requires or releases energy by comparing the bond energies of reactants with those of products - Endergonic (“energy in”)  Reactions that require a net input of energy - Exergonic (“energy out”)  Reactions that end with a net release of energy

WHY THE WORLD DOESN’T GO UP IN FLAMES Activation energy  The minimum amount of energy needed to get a reaction started  Some reactions require a lot of activation energy, others do not

ACTIVATION ENERGY

MECHANISMS OF ENZYME-MEDIATED REACTIONS Binding at enzyme active sites may bring on the transition state by 4 mechanisms  Helping substrates get together  Orienting substrates in positions that favor reaction  Inducing a fit between enzyme and substrate (induced-fit model)  Shutting out water molecules

EFFECTS OF TEMPERATURE, PH, AND SALINITY Raising the temperature boosts reaction rates by increasing a substrate’s energy  High temperatures denature enzymes Each enzyme has an optimum pH range  In humans, most enzymes work at ph 6 to 8 Salt levels affect the hydrogen bonds that hold enzymes in their three-dimensional shape

ENZYMES AND TEMPERATURE Warm = dark fur

HELP FROM COFACTORS Cofactors  Atoms or molecules (other than proteins) that are necessary for enzyme function  Example: Iron atoms in catalase Coenzymes  Organic cofactors such as vitamins  May become modified during a reaction  White board Cofactor and Coenzyme White board Cofactor and Coenzyme

CATALASE AND COFACTORS Catalase is an antioxidant that neutralizes free radicals (atoms or molecules with unpaired electrons that attack biological molecules) Catalase works by holding a substrate molecule close to one of its iron atoms (cofactors)  Iron pulls on the substrate’s electrons, bringing on the transition state  The enzyme song The enzyme song

ALLOSTERIC SITES Allosteric sites – a region away from an active site that can bind regulatory molecules Kahn Allosteric CompetitionKahn Allosteric Competition Short Allosteric RegulationShort Allosteric Regulation

FEEDBACK INHIBITION Feedback Inhibition = the end product inhibits the first enzyme in a series

BIOLUMINESCENCE Bioluminescence  Light emitted from metabolic reactions in living organisms -Bioluminescent organisms emit light when enzymes (generic = luciferases) convert chemical bond energy in luciferins to light energy luciferin + ATP → luciferin-ADP + P i luciferin-ADP + O 2 → oxyluciferin + AMP + CO 2 + light

BIOLUMINESCENCE VIDEOS National Geographic Waves Explained BBC - deep sea