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