Ch. 6.3, 6.4 & 6.5 Energy & Enzymes

_______________________ required to start the reaction energy level of reactants energy content of molecules energy level of products progress of reaction An _____________________ reaction Sparks ignite gas high low 6.2 All Chemical Reactions Require Activation Energy to Begin (History Lesson on Endo and Exo) (ex of rxn)

(b) An exergonic reaction

6.3 How is Energy Transported Within Cells  organisms powered by chemical energy supplied by ____________ breakdown of glucose  energy transferred to _____________________________(i.e. ATP)  charged by exergonic rxns and drive endergonic rxns (i.e. rechargeable batteries  ATP recycled approx. 1,400X/day (marathon runner uses a lb. of ATP/min Dehydration synthesis uses energy when making ATP from ADP.

 _________________________– energy carrier molecules that ______________energetic electrons & H+ ions  donate high-energy electrons to other molecules  NADH, FADH 2

Coupled Reactions Link Exergonic with Endergonic Reactions  _____________reaction - exergonic rxns provide energy needed to __________endergonic rxns ___________________ - plants use sunlight (____gonic) to drive _______gonic synthesis of high-energy glucose molecules from lower-energy reactants (CO 2 + H 2 O) ________________ – organisms break down glucose into CO 2 + H 2 O (_____gonic) to drive synthesis of proteins, amino acids (_____gonic)  energy is always __________________every time it is transformed  energy released (exergonic) must always exceed energy needed (endergonic)

 activation energy determines the ________ at which a reaction occurs Blue = exothermic Green = endothermic  some important chemical reactions are too slow or have a high activation energy 6.4 How Do Enzymes Promote Biochemical Reactions? reactants exothermic

 _____________ – substances that __________rates of chemical reactions w/o being used up or permanently altered (Elephant Toothpaste) (how catalytic converters work – 10 min)

Enzymes are Biological Catalysts  not advantageous to speed up dozens of rxns at once; so it is a _________________  _______________– natural catalysts (mostly proteins)  each catalyzes only a few types of rxns (most only catalyze 1 with specific molecules)  exergonic & endergonic rxns can be catalyzed  ATP synthase + ATPase (ATP Synthase)

Structure of Enzymes Allows Them to Catalyze Specific Reactions  ____________ of enzyme _______________ its ____________ (just like proteins)  structure – determined by a.a. sequence/twisted/folded  shape and charges of a.a. that form active site determines what molecules can enter (amylase  starch not cellulose; pepsin & trypsin)  some catalyze tens of thousands of rxns/sec and some act much slower (firefly)

Enzymes, Like All Catalysts, Lower Activation Energy  reactions occur in_____; each step catalyzed by different enzymes  ____________activation energy overall  reaction can occur at body temp (related to digestion)

How Are Enzymes Regulated?  metabolism – sum of all the ________________________in a cell  metabolic pathways – reactions that are linked together - ________________ step acts as the ________________________ step i.e. _______________ (synthesis of high energy molecules i.e. glucose) i.e. glycolysis (begins breakdown of glucose) Initial reactant Intermediates End products PATHWAY 1 PATHWAY 2 enzyme 1 enzyme 2 enzyme 3 enzyme 4 enzyme 5 enzyme 6 – photo & resp.

 Cells must regulate metabolic pathways by controlling ____ produced. a) type of enzymes b) quantity of enzymes c) activity levels of enzymes  for a given ____________ of enzyme, as substrate levels increase, the rxn rate ______________ until active sites of all enzymes are being continuously occupied by new substrate

 ________that code for enzymes can turn _____________ - marathon runners & high-carb meals b4 competitions -glucose enters blood & triggers metabolic rxns (i.e. pancreas releases insulin) -insulin turns on genes that code for 1 st enzyme in pathway that breaks down glucose  Some enzymes only synthesized at ________________ in organisms life (i.e. lactase)  some enzymes are synthesized in _______________ and then activated when needed (i.e. protein digesting pepsin & trypsin – work best in acidic conditions)

Enzyme Activity May be Controlled by Competitive or Noncompetitive Inhibition  Reactions ______________ by competitive inhibition and noncompetitive inhibition to prevent 1) substrates from being _________ and 2) producing _________________ product  ____________________ inhibition: substance that is not the enzyme’s normal substrate can _________________to active site of enzyme (competing for a spot) - structural similarities i.e. _________________________ (block active site of acetylcholinesterase; excess acetylcholine overstimulates muscles causing paralysis) i.e. _______________________  inhibits synthesis of bacteria cell walls; ________________________________  inhibits synthesis of molecules that contribute to swelling, pain, fever.

 ____________________ inhibition: molecule binds to a site on enzyme different from active site; ___________________; enzyme less able to catalyze rxn  (short comparison)

 _____________________: _______________________ inhibition where enzymes ___________ easily between 2 different ________ that either activate or inhibit the enzyme (i.e. ADP)  ___________________: form of ________________ regulation; causes metabolic pathways to ______________________________ when its concentration reaches an optimal level (thermostat) (feedback inhibition) As levels of isoleucine rise, isoleucine binds to the regulatory site on enzyme 1, inhibiting it intermediates enzyme 1 enzyme 2 enzyme 3 enzyme 4 enzyme 5 enzyme 1 isoleucine (end product) threonine (initial reactant)

Activity of Enzymes is Influenced by Their ____________________  enzymes have a narrow range of conditions (_________________) in which they function optimally (H-bonds btwn polar a.a.)  _______________: when enzymes lose 3-D structure required to function properly  human cellular enzymes work best around pH 7.4; human digestive enzymes work best around pH 2  __________________ affects rate of enzyme catalyzed reactions (_____________ by _______________ temps; ________________ by ________________ temps)

For pepsin, maximum activity occurs at about pH 2 For most cellular enzymes, maximum activity occurs at about pH 7.4 For trypsin, maximum activity occurs at about pH 8 rate of reaction Effect of pH on enzyme activity pH fast slow

For most human enzymes, maximum activity occurs at about 98.6  F (37  C) rate of reaction fast slow Effect of temperature on enzyme activity temperature 60 (  C) (  F)