ENZYMES BIOLOGICAL CATALYSTS
METABOLISM
• Chemical reactions of life
• forming bonds between molecules
• dehydration synthesis
• anabolic reactions
• breaking bonds between molecules
• hydrolysis
• digestion
• catabolic reactions
EXAMPLES
EXAMPLES
CHEMICAL REACTIONS & ENERGY
• Some chemical reactions release energy
• Exergonic
• ex. hydrolysis (catabolism), digesting polymers
• Some chemical reactions require input of energy
• Endergonic
• ex. dehydration synthesis (anabolism), building polymers
ANABOLISM & CATABOLISM OF ATP
ENDERGONIC VS. EXERGONIC REACTIONS
ENERGY & LIFE• Organisms require energy to live
• Where does that energy come from?
• Coupling exergonic (energy releasing) with endergonic (energy needing) reactions
PROPERTIES OF ENZYMES
• Do not cause reactions
• Function by lowering activation energy, thus, increasing reaction rates
• Are not used up by reaction
• Work best under certain temp and pH
• Are substrate specific (induced fit)
• May require cofactors or coenzymes
• May be inhibited
ACTIVATION ENERGY
• Breaking down large molecules requires an initial input of energy = activation energy
• large biomolecules are stable —> must absorb energy to break bonds
REDUCING ACTIVATION ENERGY
• Catalysts
• Reduce amount of energy needed to start a reaction
ENZYME VOCABULARY
• Substrate- reactant which binds to enzyme
• Enzyme-substrate complex- Temporary formation of bonded enzyme and substrate
• Product- End result of reaction
• Active site- Enzyme’s catalytic site; substrate fits here
HOW DOES IT WORK?
• Variety of mechanisms to lower activation energy and speed up reactions
• Synthesis
• Active site orients substrates in correct position for reaction; brings substrates closer together
• Digestion
• Active site binds substrate and puts stress on bonds that must be broken, making it easer to separate molecules
ENZYME ACTIVITY
ENZYME ACTIVITY
NAMING CONVENTIONS
• Enzymes named for reaction they catalyze:
• Sucrase breaks down sucrose
• Proteases break down proteins
• Lipases break down lipids
• DNA Polymerase combines nucleotides to create polymer DNA strand
• Pepsin breaks down proteins (polypeptides
FACTORS AFFECTING ENZYME FUNCTION
• Enzyme concentration
• Substrate concentration
• Temperature
• pH
• Salinity
• Activators
• Inhibitors
ALLOSTERIC ENZYME
• Enzyme has receptor site other than active site
• Molecule binding to this site controls shape of active site
• May turn active site on or off
FEEDBACK INHIBITION
• Enzyme’s activity is inhibited by its product
INHIBITORS
• Stop enzyme function by binding
• Can be reversible or irreversible
• Competitive inhibitors= Block substrate by entering the active site (compete for site)
• Noncompetitive inhibitors= Bind to a different site on the enzyme that causes conformational change of active site
• Ex. poisons, venom, heavy metals
PROPOSED ENZYME MODELS
• Lock and Key Model
• Simplistic model of enzyme action
• Substrate fits into 3D structure of enzyme active site
• Hydrogen bonds between the substrate and enzyme form
• “Key fits into a lock”
• Induced Fit Model
• More accurate model of enzyme action
• Substrate binding causes enzyme to change shape leading to a tighter fit
• “Conformational change”
PROPOSED ENZYME MODELS
COENZYMES & COFACTORS
• Cofactors- Non-protein compounds that are required for an enzyme’s activity (ex. zinc, iron)
• Coenzymes are a type of cofactor but are organic (NAD, vitamins)
NAD AS A COENZYME
• Super important in cellular function!!
• Originates from vitamin B3—> connection?
• NAD and NADP the most abundant coenzymes in eukaryotic cells