Factors Affecting Enzymes PDF

Enzyme Properties and Factors Affecting Enzymes AP Biology  Enzymes ▪ Biological catalysts ◆ proteins (& RNA) ◆ facilitate chemical reactions ▪ increase rate of reaction without being consumed ▪ reduce activation energy ▪ don’t chang...

Enzyme Properties and Factors Affecting Enzymes AP Biology  Enzymes ▪ Biological catalysts ◆ proteins (& RNA) ◆ facilitate chemical reactions ▪ increase rate of reaction without being consumed ▪ reduce activation energy ▪ don’t change free energy (ΔG) released or required ◆ required for most biological reactions ◆ highly specific ▪ thousands of different enzymes in cells ◆ control reactions of life AP Biology  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 active site substrate products enzyme AP Biology  Properties of enzymes ▪ Reaction specific ◆ each enzyme works with a specific substrate ▪ chemical fit between active site & substrate ⬥ H bonds & ionic bonds ▪ Not consumed in reaction ◆ single enzyme molecule can catalyze thousands or more reactions per second ▪ enzymes unaffected by the reaction ▪ Affected by cellular conditions ◆ any condition that affects protein structure ▪ temperature, pH, salinity AP Biology  Naming conventions ▪ Enzymes named for reaction they catalyze ◆ sucrase breaks down sucrose ◆ proteases break down proteins ◆ lipases break down lipids ◆ DNA polymerase builds DNA ▪ adds nucleotides to DNA strand ◆ pepsin breaks down proteins (polypeptides) AP Biology  Lock and Key model ▪ Simplistic model of enzyme action In biology… Shape matters! ◆ substrate fits into 3-D structure of enzyme’ active site ▪ H bonds between substrate & enzyme ◆ like “key fits into lock” AP Biology  Induced fit model ▪ More accurate model of enzyme action ◆ 3-D structure of enzyme fits substrate ◆ substrate binding cause enzyme to change shape leading to a tighter fit ▪ “conformational change” ▪ bring chemical groups in position to catalyze reaction AP Biology  How do enzymes speed up reactions? ▪ Variety of mechanisms to lower activation energy & speed up reaction ◆ synthesis ▪ active site orients substrates in correct position for reaction ⬥ enzyme brings substrate closer together ◆ digestion ▪ active site binds substrate & puts stress on bonds that must be broken, making it easier to separate molecules AP Biology  Got any Questions?! AP Biology 2007-2008  Factors that Affect Enzymes AP Biology 2007-2008  Factors Affecting Enzyme Function ▪ Enzyme concentration ▪ Substrate concentration ▪ Temperature ▪ pH ▪ Salinity ▪ Activators ▪ Inhibitors AP Biology catalase  Enzyme concentration What happens as enzyme concentration increases?! reaction rate enzyme concentration AP Biology - substrate concentration stays same  Factors affecting enzyme function ▪ Enzyme concentration ◆ as ↑ enzyme = ↑ reaction rate ▪ more enzymes = more frequently collide with substrate ◆ reaction rate levels off ▪ substrate becomes limiting factor ▪ not all enzyme molecules can find substrate reaction rate AP Biology enzyme concentration  Substrate concentration What happens as substrate concentration increases?! reaction rate substrate concentration AP Biology - enzyme concentration stays the same  Factors affecting enzyme function ▪ Substrate concentration ◆ as ↑ substrate = ↑ reaction rate ▪ more substrate = more frequently collide with enzyme ◆ reaction rate levels off ▪ all enzymes have active site engaged ▪ enzyme is saturated ▪ maximum rate of reaction reaction rate AP Biology substrate concentration  Temperature What is ideal temperature for this enzyme?! reaction rate 37° temperature AP Biology  Factors affecting enzyme function ▪ Temperature ◆ Optimum Temperature° ▪ greatest number of molecular collisions ▪ human enzymes = 35°- 40°C ⬥ body temp = 37°C ◆ Heat: increase beyond optimum T° ▪ increased energy level of molecules disrupts bonds in enzyme & between enzyme & substrate ▪ denaturation = lose 3D shape (3° structure) ◆ Cold: decrease T° ▪ molecules move slower AP Biology ▪ decrease collisions between enzyme & substrate  Enzymes and temperature ▪ Different enzymes function in different organisms in different environments hot spring human enzyme bacteria enzyme reaction rate 37°C 70°C AP Biology temperature (158°F)  How do ectotherms do it? AP Biology  pH What changes in pH are happening during digestion? pepsin trypsin reaction rate pepsin trypsin 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 AP Biology pH  Factors affecting enzyme function ▪ pH ◆ changes in pH ▪ adds or remove H+ ▪ disrupts bonds, disrupts 3D shape ⬥ disrupts attractions between charged amino acids ⬥ affect 2° & 3° structure ⬥ denatures protein ◆ optimal pH? ▪ most human enzymes = pH 6-8 ⬥ depends on localized conditions ⬥ pepsin (stomach) = pH 2-3 ⬥ trypsin (small intestines) = pH 8 AP Biology 0 1 2 3 4 5 6 7 8 9 10 11  Salinity What’s happening here?! reaction rate salt concentration AP Biology  Factors affecting enzyme function ▪ Salt concentration ◆ changes in salinity ▪ adds or removes cations (+) & anions (–) ▪ disrupts bonds, disrupts 3D shape ⬥ disrupts attractions between charged amino acids ⬥ affect 2° & 3° structure ⬥ denatures protein ◆ enzymes intolerant of extreme salinity ▪ Dead Sea is called dead for a reason! AP Biology  Compounds which help enzymes ▪ Activators Fe in hemoglobin ◆ cofactors ▪ non-protein, small inorganic compounds & ions ⬥ Mg, K, Ca, Zn, Fe, Cu ⬥ bound within enzyme molecule ◆ coenzymes ▪ non-protein, organic molecules ⬥ bind temporarily or permanently to enzyme near active site Mg in ▪ many vitamins chlorophyll ⬥ NAD (niacin; B3) ⬥ FAD (riboflavin; B2) AP Biology ⬥ Coenzyme A  Compounds which regulate enzymes ▪ Inhibitors ◆ molecules that reduce enzyme activity ◆ competitive inhibition ◆ noncompetitive inhibition ◆ irreversible inhibition ◆ feedback inhibition AP Biology  Competitive Inhibitor ▪ Inhibitor & substrate “compete” for active site ◆ penicillin blocks enzyme bacteria use to build cell walls ◆ disulfiram (Antabuse) treats chronic alcoholism ▪ blocks enzyme that breaks down alcohol ▪ severe hangover & vomiting 5-10 minutes after drinking ▪ Overcome by increasing substrate concentration ◆ saturate solution with substrate so it out-competes inhibitor for active site on enzyme AP Biology  Non-Competitive Inhibitor ▪ Inhibitor binds to site other than active site ◆ allosteric inhibitor binds to allosteric site ◆ causes enzyme to change shape ▪ conformational change ▪ active site is no longer functional binding site ⬥ keeps enzyme inactive ◆ some anti-cancer drugs inhibit enzymes involved in DNA synthesis ▪ stop DNA production ▪ stop division of more cancer cells ◆ cyanide poisoning irreversible inhibitor of Cytochrome C, an enzyme in cellular respiration ▪ stops production of ATP AP Biology  Irreversible inhibition ▪ Inhibitor permanently binds to enzyme ◆ competitor ▪ permanently binds to active site ◆ allosteric ▪ permanently binds to allosteric site ▪ permanently changes shape of enzyme ▪ nerve gas, sarin, many insecticides (malathion, parathion…) ⬥ cholinesterase inhibitors doesn’t breakdown the neurotransmitter, acetylcholine AP Biology  Allosteric regulation ▪ Conformational changes by regulatory molecules ◆ inhibitors ▪ keeps enzyme in inactive form ◆ activators ▪ keeps enzyme in active form Conformational AP Biology changes Allosteric regulation  Metabolic pathways A→B→C→D→E→F→ G A→B→C→D→E→F→G → → → → → → enzyme enzyme enzyme enzyme enzyme enzyme 1 2 3 4 5 6 ▪ Chemical reactions of life are organized in pathways ◆ divide chemical reaction into many small steps ▪ artifact of evolution ▪ ↑ efficiency ⬥ intermediate branching points AP Biology ▪ ↑ control = regulation  Efficiency ▪ Organized groups of enzymes ◆ enzymes are embedded in membrane and arranged sequentially ▪ Link endergonic & exergonic reactions Whoa! All that going on in those little mitochondria! AP Biology  Feedback Inhibition ▪ Regulation & coordination of production ◆ product is used by next step in pathway ◆ final product is inhibitor of earlier step ▪ allosteric inhibitor of earlier enzyme ▪ feedback inhibition ◆ no unnecessary accumulation of product A→B→C→D→E→F→G → → → → → → X enzyme enzyme enzyme enzyme enzyme enzyme 1 2 3 4 5 6 AP Biology allosteric inhibitor of enzyme 1  threonine Feedback inhibition ▪ Example ◆ amino acid synthesis of isoleucine from threonine ◆ isoleucine becomes the allosteric inhibitor of the first step in the pathway ▪ 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