Enzymes AP Biology 2007 2008 Exothermic vs endothermic

Enzymes AP Biology 2007 -2008

Exothermic vs. endothermic reactions exothermic endothermic - energy invested - synthesis - energy released - digestion + G - G All chemical reactions require energy AP Biology G = change in free energy = ability to do work

Activation energy § Breaking down large molecules requires an initial input of energy activation energy u large biomolecules are stable u must absorb energy to break bonds u AP Biology cellulose energy CO 2 + H 2 O + heat

Too much activation energy for life § Activation energy u moves the reaction over an “energy hill” glucose AP Biology Why is activation energy important? ?

Reducing Activation energy § Catalysts u reducing the amount of energy to start a reaction uncatalyzed reaction Pheeew… that takes a lot less energy! catalyzed reaction NEW activation energy reactant AP Biology product

Catalysts § So what’s a cell got to do to reduce activation energy? u get help! … chemical help… ENZYMES Call in the ENZYMES! G AP Biology The ENZYMES are here

Enzymes § Biological catalysts u u Proteins facilitate chemical reactions § increase rate of reaction without being consumed § reduce activation energy § don’t change free energy ( G) released or required u u required for most biological reactions highly specific § thousands of different enzymes in cells u AP Biology control reactions of life

Enzymes vocabulary substrate § reactant which binds to enzyme § enzyme-substrate complex: temporary association product § end result of reaction active site § enzyme’s catalytic site; substrate fits into active site substrate enzyme AP Biology active site products

Lock and Key model § Simplistic model of enzyme action u substrate fits into 3 -D structure of enzyme’ active site § H bonds between substrate & enzyme u AP Biology like “key fits into lock” In biology… Size doesn’t matter… Shape matters!

Induced fit model § More accurate model of enzyme action 3 -D structure of enzyme fits substrate u substrate binding cause enzyme to change shape leading to a tighter fit u § “conformational change” § bring chemical groups in position to catalyze reaction AP Biology

Properties of enzymes § Reaction specific u each enzyme works with a specific substrate w H bonds & ionic bonds between active site and substrate § Not consumed in reaction u single enzyme molecule can catalyze thousands or more reactions per second § Affected by cellular conditions u any condition that affects protein structure § temperature, p. H, salinity - Denaturation AP Biology

Naming conventions § Enzymes named for reaction they catalyze u u sucrase breaks down sucrose proteases break down proteins lipases break down lipids DNA polymerase builds DNA § adds nucleotides to DNA strand u pepsin breaks down proteins (polypeptides) AP Biology

Got any Questions? ! AP Biology 2007 -2008

Factors that Affect Enzymes AP Biology 2007 -2008

Enzyme concentration reaction rate as enzyme = reaction rate enzyme concentration AP Biology What’s happening here? !

Substrate concentration reaction rate as substrate = reaction rate substrate concentration AP Biology What’s happening here? !

Temperature Optimum T° greatest number of molecular collisions cule n Slow atio mole atur reaction rate Den s What’s happening here? ! 37° temperature AP Biology Optimal To

Enzymes and temperature § Different enzymes function in different organisms in different environments reaction rate human enzyme hot spring bacteria enzyme 37°C AP Biology temperature 70°C (158°F)

p. H What’s happening here? ! trypsin reaction rate pepsin trypsin 0 AP Biology 1 2 3 4 5 6 p. H 7 8 9 10 11 12 13 14

Salinity reaction rate Salinity is salt concentration AP Biology What’s happening here? !

IMPORTANT!!!!! So sit up! Compounds which help enzymes cofactors § non-protein § small inorganic compounds & ions w bound within enzyme molecule § Examples: w Mg, K, Ca, Zn, Fe, Cu coenzymes § non-protein § organic molecules w bind temporarily or permanently to enzyme near active site § Examples: § many vitamins w NAD (niacin; B 3) w FAD (riboflavin; B 2) w Coenzyme A AP Biology

Show me some coenzymes homeskillet! Fe in hemoglobin Mg in chlorophyll AP Biology

Compounds which regulate enzymes § Inhibitors molecules that reduce enzyme activity u competitive inhibition u noncompetitive inhibition u feedback inhibition u AP Biology

Competitive Inhibitor § Inhibitor & substrate “compete” for active site u disulfiram (Antabuse) treats chronic alcoholism § blocks enzyme that breaks down alcohol § severe hangover & vomiting 5 -10 minutes after drinking How can I beat a competitive inhibitor? AP Biology

Non-Competitive Inhibitor § Inhibitor binds to site other than active site u u allosteric inhibitor binds to allosteric site causes enzyme to change shape § conformational change § active site is no longer functional binding site w keeps enzyme inactive AP Biology

Metabolic pathways 2 1 A B C D E F G 5 6 enzyme enzyme 3 4 § Many enzymes are used in chemical reactions § efficiency § control = regulation When might Inhibitors be helpful? AP Biology

Feedback Inhibition § Regulation & coordination of production u u product is used by next step in pathway final product is inhibitor of earlier step § allosteric inhibitor of earlier enzyme § feedback inhibition u no unnecessary accumulation of product A B C D E F G 1 2 3 4 5 6 X enzyme enzyme AP Biology allosteric inhibitor of enzyme 1

Feedback inhibition threonine § Example synthesis of amino acid, isoleucine from amino acid, threonine u isoleucine becomes the allosteric inhibitor of the first step in the pathway u § as product accumulates it collides with enzyme more often than substrate does AP Biology isoleucine

Don’t be inhibited! Ask Questions! AP Biology 2007 -2008

Extra Info AP Biology

Factors affecting enzyme function § p. H u changes in p. H § adds or remove H+ § disrupts bonds, disrupts 3 D shape w disrupts attractions between charged amino acids w affect 2° & 3° structure w denatures protein u optimal p. H? § most human enzymes = p. H 6 -8 w depends on localized conditions w pepsin (stomach) = p. H 2 -3 w trypsin (small intestines) = p. H 8 AP Biology 0 1 2 3 4 5 6 7 8 9 10 11

Factors affecting enzyme function § Salt concentration u changes in salinity § adds or removes cations (+) & anions (–) § disrupts bonds, disrupts 3 D shape w disrupts attractions between charged amino acids w affect 2° & 3° structure w denatures protein u enzymes intolerant of extreme salinity § Dead Sea is called dead for a reason! AP Biology