AP Biology. From food webs to the life of a cell. Metabolism & Enzymes. Flow of energy through life. Metabolism. Chemical reactions of life

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1 From food webs to the life of a cell energy Metabolism & Enzymes energy energy Flow of energy through life Life is built on chemical reactions sun transforming energy from one form to another organic molecules ATP & organic molecules organic molecules ATP & organic molecules Metabolism Chemical reactions of life between molecules dehydration synthesis synthesis between molecules hydrolysis digestion solar energy AP ATP Biology & organic molecules That s why they re called anabolic steroids! 1

2 Examples dehydration synthesis (synthesis) + Examples dehydration synthesis (synthesis) H 2 O hydrolysis (digestion) hydrolysis (digestion) + H 2 O Chemical reactions & energy Some chemical reactions release energy digesting polymers digesting molecules= LESS organization= lower energy state hydrolysis = catabolism Some chemical reactions require input of energy building polymers dehydration synthesis = anabolism building molecules= MORE organization= higher energy state Endergonic vs. exergonic reactions exergonic endergonic - energy released - digestion -ΔG - energy invested - synthesis +ΔG ΔG = change in free energy = ability to do work 2

3 Energy & life Organisms require energy to live where does that energy come from? synthesis coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy) + + energy What drives reactions? If reactions are downhill, why don t they just happen spontaneously? because covalent bonds are stable bonds starch Why don t stable polymers spontaneously digest into their monomers? synthesis + + energy Activation energy Breaking down large molecules requires an initial input of energy large biomolecules are stable must absorb energy to break bonds Too much activation energy for life Activation energy amount of energy needed to destabilize the bonds of a molecule moves the reaction over an energy hill glucose Not a match! That s too much energy to expose living cells to! cellulose energy CO 2 + H 2 O + heat 3

4 Reducing Activation energy reducing the amount of energy to start a reaction uncatalyzed reaction uncatalyzed reaction Pheeew that takes a lot less energy! Catalysts So what s a cell got to do to reduce activation energy? get help! chemical help Call in the ENZYMES! NEW activation energy reactant ΔG product Enzymes Biological catalysts increase rate of reaction without being consumed reduce activation energy don t change free energy (ΔG) released or required required for most biological reactions thousands of different s in cells control reactions of life Enzymes vocabulary reactant which binds to -substrate complex: temporary association end result of reaction s catalytic site; substrate fits into active site substrate active site products 4

5 Properties of s _ each works with a specific substrate chemical fit between active site & substrate H bonds & ionic bonds _ single molecule can catalyze thousands or more reactions per second s unaffected by the reaction _ any condition that affects protein structure temperature, ph, salinity Naming conventions Enzymes named for reaction they catalyze breaks down sucrose break down proteins break down lipids builds DNA adds nucleotides to DNA strand breaks down proteins (polypeptides) Lock and Key model Simplistic model of action substrate fits into 3-D structure of active site H bonds between substrate & like key fits into lock In biology Size doesn t matter Shape matters! Induced fit model More accurate model of action 3-D structure of fits substrate substrate binding cause to change shape leading to a tighter fit conformational change bring chemical groups in position to catalyze reaction 5

6 How does it work? Variety of mechanisms to lower activation energy & speed up reaction synthesis active site orients substrates in correct position for reaction brings substrate closer together digestion active site binds substrate & puts stress on bonds that must be broken, making it easier to separate molecules Got any Questions?! Factors that Affect Enzymes Factors Affecting Enzyme Function catalase 6

7 Enzyme concentration concentration What s happening here?! Factors affecting function Enzyme concentration as = more s = more frequently collide with substrate levels off substrate becomes limiting factor not all molecules can find substrate concentration Substrate concentration substrate concentration What s happening here?! Factors affecting function Substrate concentration as substrate = more substrate = more frequently collide with levels off all s have active site engaged is saturated maximum rate of reaction substrate concentration 7

8 Temperature 37 temperature What s happening here?! Factors affecting function Temperature greatest number of molecular collisions human s = C body temp = 37 C increased energy level of molecules disrupts bonds in & between & substrate H, ionic = weak bonds = lose 3D shape (3 structure) molecules move slower decrease collisions between & substrate Enzymes and temperature Different s function in different organisms in different environments human hot spring bacteria How do ectotherms do it? 37 C temperature 70 C (158 F) 8

9 ph pepsin trypsin What s happening here?! trypsin ph pepsin Factors affecting function ph changes in ph adds or remove H + disrupts attractions between charged amino acids affect 2 & 3 structure denatures protein optimal ph? most human s = ph 6-8 depends on localized conditions pepsin (stomach) = ph 2-3 trypsin (small intestines) = ph Salinity What s happening here?! Factors affecting function Salt concentration changes in salinity adds or removes cations (+) & anions ( ) disrupts attractions between charged amino acids affect 2 & 3 structure denatures protein s intolerant of extreme salinity Dead Sea is called dead for a reason! salt concentration 9

10 Compounds which help s Activators non-protein, small inorganic compounds & ions Mg, K, Ca, Zn, Fe, Cu Fe in hemoglobin bound within molecule non-protein, organic molecules bind temporarily or permanently to near active site many vitamins NAD (niacin; B3) FAD (riboflavin; B2) Co A Mg in chlorophyll Compounds which regulate s Inhibitors molecules that reduce activity Competitive Inhibitor Inhibitor & substrate compete for active site penicillin blocks bacteria use to build cell walls disulfiram (Antabuse) treats chronic alcoholism blocks 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 Non-Competitive Inhibitor Inhibitor binds to site other than active site causes to change shape conformational change active site is no longer functional binding site keeps inactive some anti-cancer drugs inhibit s involved in DNA synthesis stop DNA production stop division of more cancer cells cyanide poisoning irreversible inhibitor of Cytochrome C, an in cellular respiration stops production of ATP 10

11 Irreversible inhibition Inhibitor permanently binds to permanently binds to active site permanently binds to allosteric site permanently changes shape of nerve gas, sarin, many insecticides (malathion, parathion ) cholinesterase inhibitors doesn t breakdown the neurotransmitter, acetylcholine Allosteric regulation Conformational changes by regulatory molecules inhibitors keeps in inactive form activators keeps in active form Conformational changes Allosteric regulation Metabolic pathways A B C D E F G Chemical reactions of life are organized in pathways divide chemical reaction into many small steps artifact of evolution efficiency intermediate branching points control = regulation 5 6 Efficiency Organized groups of s s are embedded in membrane and arranged sequentially Link endergonic & exergonic reactions Whoa! All that going on in those little mitochondria! 11

12 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 no unnecessary accumulation of product A B C D E F G X allosteric inhibitor of 1 Feedback inhibition Example synthesis of amino acid, isoleucine from amino acid, threonine isoleucine becomes the allosteric inhibitor of the first step in the pathway as product accumulates it collides with more often than substrate does threonine isoleucin e Don t be inhibited! Ask Questions!