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Transcript
Metabolism & Enzymes AP Biology 2007-2008 From food webs to the life of a cell energy energy energy AP Biology Flow of energy through life Life is built on chemical reactions Transforming energy from one form to another Most reactions are spontaneous organic molecules ATP & organic molecules sun solar energy AP Biology ATP & organic molecules organic molecules ATP & organic molecules Metabolism All the chemical reactions that take place in a cell Enzymes regulate metabolic pathways Metabolic Pathway Set of enzyme-catalyzed reactions that relate reactants and products (biochemical pathways) Substrate product = substrate final pathway’s product Final product can fit in to Enzyme 1 – stop reaction What is this called? AP Biology Metabolism Chemical reactions of life forming bonds between molecules dehydration synthesis synthesis anabolic - consumption of energy to build complex molecules from small molecules Glucose starch CO2 + H2OC6H12O6 + O2 Photosynthesis AP Biology That’s why they’re called anabolic steroids! Metabolism breaking bonds between molecules hydrolysis digestion catabolic reactions - release energy by breaking down complex molecules into simpler molecules. Ex. Starch glucose (net loss) AP Biology That’s why they’re called anabolic steroids! Examples dehydration synthesis (synthesis) + enzyme H2O hydrolysis (digestion) enzyme H2O AP Biology + Examples dehydration synthesis (synthesis) enzyme hydrolysis (digestion) enzyme AP Biology Energy The ability to do work The 1st law of Thermodynamics Energy cannot be created or destroyed It can only be transformed from one type into another Heat is the ultimate form of energy – last step of transformation AP Biology The 2nd law of thermodynamics Every energy transformation increases the entropy (disorder of the universe) K Free Energy – The amount of energy available to a system (∆G) AP Biology Chemical reactions & energy Some chemical reactions net release of free energy exergonic Energy now available from the breakdown digesting polymers hydrolysis = catabolism digesting molecules= Spontaneous LESS organization= -G AP Biology lower energy state Link for you to study at home exergonic - Spontaneous w/ enzyme lowers activation energy -G AP Biology G = change in free energy = ability to do work Some chemical reactions require net input of energy endergonic building polymers Absorbs free energy from surroundings Net gain of energy building molecules= MORE organization= higher energy state AP Biology Endergonic vs. exergonic reactions endergonic Glucose A.E. from light captured CO2 +H2O AP Biology Net energy captured by synthesizing glucose - energy invested - synthesis +G Energy & life Organisms require energy to live where does that energy come from? coupling exergonic reactions (releasing energy) with endergonic reactions (needing energy) + digestion synthesis + AP Biology + energy + energy Starch Glycogen Glucose Exergonic reactions drive Endergonic Reactions (Catabolic) (anabolic) ATP Synthase – hydrogen fed into synthase, energy, happens in mitochondria, ADP ATP AP Biology ATP synthase (extra for now) Enzyme channel in H+ H+ H+ H+ H+ H+ H+ H+ rotor mitochondrial membrane permeable to H+ H+ flow down concentration gradient rod flow like water over water wheel flowing H+ cause ADP + P change in shape of ATP synthase enzyme powers bonding of ATP Pi to ADP: ADP + Pi ATP APBut… Biology How is the proton (H+) gradient formed? catalytic head H+ What drives reactions? If reactions are “downhill”, why don’t they just happen spontaneously? because covalent bonds are stable bonds starch AP Biology Why don’t stable polymers spontaneously digest into their monomers? Adenine Triphosphate (ATP) ATP powers cellular work by coupling exergonic and endergonic reactions ATP changes the shape of a molecule causes work then molecule goes back to original shape Phosphorylation – the energy from the hydrolysis of ATP is directly coupled to endergonic processes by the transfer of the phosphate group to another molecule The recipient molecule is phosphorylated AP Biology ATP / ADP cycle Can’t store ATP cellular good energy donor, not good energy storage respiration too reactive transfers Pi too easily only short term energy storage carbohydrates & fats are long term energy storage Whoa! Pass me the glucose (and O2)! AP Biology ATP 7.3 kcal/mole ADP + Pi A working muscle recycles over 10 million ATPs per second 1. Reatants 2. Products 3. Activation Energy 4. Transition State 5. Ea w/ enzyme 6. + or -G 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 (G) released or required required for most biological reactions highly specific thousands of different enzymes in cells 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 active site substrate enzyme AP Biology products Lock and Key model Simplistic model of enzyme action substrate fits into 3-D structure of enzyme’ active site H bonds between substrate & enzyme 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 substrate binding cause enzyme to change shape leading to a tighter fit “conformational change” bring chemical groups in position to catalyze reaction AP Biology Factors that Affect Enzymes AP Biology 2007-2008 Factors Affecting Enzyme Function Enzyme concentration Substrate concentration Temperature pH Salinity Activators Inhibitors AP Biology catalase Mr Z – Draw Picture of Enzyme on board AP Biology Compounds which help enzymes Fe in Activators 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 AP Biology many vitamins NAD (niacin; B3) FAD (riboflavin; B2) Coenzyme A Mg in chlorophyll 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 AP Biology saturate solution with substrate so it out-competes inhibitor for active site on enzyme 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 AP Biology doesn’t breakdown the neurotransmitter, acetylcholine Allosteric regulation Conformational changes by regulatory molecules inhibitors keeps enzyme in inactive form activators keeps enzyme in active form AP Biology Conformational changes Allosteric regulation Metabolic pathways ABCDEFG 5 6 enzyme enzyme enzyme enzyme enzyme enzyme enzyme 1 2 3 4 Chemical reactions of life are organized in pathways AP Biology divide chemical reaction into many small steps artifact of evolution efficiency intermediate branching points control = regulation Efficiency – This slide is extra 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 ABCDEFG 1 2 3 4 5 6 X enzyme enzyme enzyme enzyme enzyme enzyme AP Biology allosteric inhibitor of enzyme 1 threonine 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 enzyme more often than substrate does Other example – insulin, oxytocin AP Biology isoleucin e Don’t be inhibited! Ask Questions! AP Biology 2007-2008 Ghosts of Lectures Past (storage) AP Biology 2007-2008 Cooperativity Substrate acts as an activator substrate causes conformational change in enzyme induced fit favors binding of substrate at 2nd site makes enzyme more active & effective hemoglobin Hemoglobin 4 polypeptide chains can bind 4 O2; 1st O2 binds now easier for other O2 to bind AP3Biology