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That’s why they’re called anabolic steroids!
Metabolism Chemical reactions of life _____________ bonds between molecules dehydration synthesis synthesis ______________ reactions hydrolysis digestion _______________ reactions That’s why they’re called anabolic steroids!
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Examples dehydration synthesis (synthesis) hydrolysis (digestion)
enzyme + H2O hydrolysis (digestion) enzyme + H2O
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Examples dehydration synthesis (synthesis) hydrolysis (digestion)
enzyme hydrolysis (digestion) enzyme
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Chemical reactions & energy
Some chemical reactions _______ energy _____________________ digesting polymers hydrolysis = catabolism Some chemical reactions require ____________of energy ________________ building polymers dehydration synthesis = anabolism digesting molecules= LESS organization= lower energy state building molecules= MORE organization= higher energy state
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Endergonic vs. exergonic reactions
- energy released - digestion energy invested synthesis +G -G G = change in free energy = ability to do work
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Energy & life Organisms require energy to live
where does that energy come from? ___________ _____________ reactions (releasing energy) with ____________ reactions (needing energy) energy + + digestion synthesis energy + +
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Where the Energy of Life Comes From:
_________________________ Light energy is used to assemble water and CO2 into larger and more complex glucose molecules __________________ Pathway Pathway that consumes energy (LIGHT) to build _________________ (_____________) molecules from _____________ ones (________ and _________) _____________________________ Products are storing more energy than were reactants Like pushing a bolder up a hill Requires and continual input of energy to make it happen (i.e. SUNLIGHT)
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Where the Energy of Life Comes From:
______________________________ _______________ is broken apart and the energy contained its C-H bonds is ___________ _____________________ Pathway Pathway that releases energy (_______) from _______________ molecules (glucose) in order to do work ___________________________ Reactants contain __________ energy than do products Like pushing a bolder off a cliff Just needs a nudge and it will go
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What controls exergonic reactions?
If exergonic reactions are “downhill”, why don’t they just happen spontaneously? because covalent bonds are ______ bonds Why don’t stable polymers spontaneously digest into their monomers? starch
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Activation energy Breaking down large molecules requires an initial input of energy __________________________ large biomolecules are ____________ must absorb energy to _______________________ Need a spark to start a fire energy cellulose CO2 + H2O + heat
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Too much activation energy for life
amount of energy needed to ______________ the bonds of a molecule moves the reaction over an “energy ________” Not a match! That’s too much energy to expose living cells to! glucose 2nd Law of thermodynamics Universe tends to disorder so why don’t proteins, carbohydrates & other biomolecules breakdown? at temperatures typical of the cell, molecules don’t make it over the hump of activation energy but, a cell must be metabolically active heat would speed reactions, but… would denature proteins & kill cells
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_______________ Activation energy
_________________________ reducing the amount of energy to start a reaction Pheeew… that takes a lot less energy! ____________ reaction ____________ reaction NEW ___________________ reactant product
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Catalysts So what’s a cell got to do to reduce activation energy?
get help! … chemical help… ____________ Call in the ENZYMES! G
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Enzymes ________________________ proteins (& RNA)
facilitate chemical reactions __________ rate of reaction without being _________ ___________ activation energy don’t change _____________ (G) released or required _________________ for most biological reactions highly ________________________ thousands of different enzymes in cells control reactions of life
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Enzymes vocabulary _________________ ___________________
reactant which binds to enzyme enzyme-substrate complex: temporary association ___________________ end result of reaction _______________________ enzyme’s catalytic site; substrate fits into active site active site products substrate enzyme
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Properties of enzymes Reaction _________________
each enzyme works with a specific substrate chemical fit between active site & substrate H bonds & ionic bonds _______ 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 _____________, ______, _______________
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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)
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In biology… Size doesn’t matter… Shape matters!
Lock and Key model Simplistic model of enzyme action substrate fits into 3-D structure of enzyme’ active site H bonds between substrate & enzyme like “key fits into lock” In biology… Size doesn’t matter… Shape matters!
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____________________ model
More accurate model of enzyme action 3-D structure of enzyme fits substrate substrate binding cause enzyme to ________________ leading to a tighter fit “_____________________ change” Like a ____________ in ____________ bring chemical groups in position to catalyze reaction
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How does it work? Variety of mechanisms to lower activation energy & speed up reaction synthesis active site ____________substrates in correct position for reaction enzyme brings substrate closer together digestion active site binds substrate & puts ________ on bonds that must be broken, making it easier to separate molecules
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Factors that Affect Enzymes
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Factors Affecting Enzyme Function
Enzyme concentration Substrate concentration Temperature pH Salinity Activators Inhibitors Living with oxygen is dangerous. We rely on oxygen to power our cells, but oxygen is a reactive molecule that can cause serious problems if not carefully controlled. One of the dangers of oxygen is that it is easily converted into other reactive compounds. Inside our cells, electrons are continually shuttled from site to site by carrier molecules, such as carriers derived from riboflavin and niacin. If oxygen runs into one of these carrier molecules, the electron may be accidentally transferred to it. This converts oxygen into dangerous compounds such as superoxide radicals and hydrogen peroxide, which can attack the delicate sulfur atoms and metal ions in proteins. To make things even worse, free iron ions in the cell occasionally convert hydrogen peroxide into hydroxyl radicals. These deadly molecules attack and mutate DNA. Fortunately, cells make a variety of antioxidant enzymes to fight the dangerous side-effects of life with oxygen. Two important players are superoxide dismutase, which converts superoxide radicals into hydrogen peroxide, and catalase, which converts hydrogen peroxide into water and oxygen gas. The importance of these enzymes is demonstrated by their prevalence, ranging from about 0.1% of the protein in an E. coli cell to upwards of a quarter of the protein in susceptible cell types. These many catalase molecules patrol the cell, counteracting the steady production of hydrogen peroxide and keeping it at a safe level. Catalases are some of the most efficient enzymes found in cells. Each catalase molecule can decompose millions of hydrogen peroxide molecules every second. The cow catalase shown here and our own catalases use an iron ion to assist in this speedy reaction. The enzyme is composed of four identical subunits, each with its own active site buried deep inside. The iron ion, shown in green, is gripped at the center of a disk-shaped heme group. Catalases, since they must fight against reactive molecules, are also unusually stable enzymes. Notice how the four chains interweave, locking the entire complex into the proper shape. catalase
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Enzyme concentration reaction rate enzyme concentration
What’s happening here?! reaction rate enzyme concentration
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Factors affecting enzyme function
Enzyme concentration as __ enzyme conc. = __ reaction rate more enzymes = more frequent collisions with substrate reaction rate ______________ substrate becomes _____________ factor not all enzyme molecules can find substrate Why is it a good adaptation to organize the cell in organelles? Sequester enzymes with their substrates! enzyme concentration reaction rate
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Substrate concentration
What’s happening here?! reaction rate substrate concentration
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Factors affecting enzyme function
Substrate concentration as __ substrate = __ reaction rate more substrate = more frequent _________ with enzyme reaction rate levels off all enzymes have active site engaged enzyme is ____________ maximum rate of reaction Why is it a good adaptation to organize the cell in organelles? Sequester enzymes with their substrates! substrate concentration reaction rate
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Temperature What’s happening here?! 37° reaction rate temperature
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Factors affecting enzyme function
Temperature _____________ T° greatest number of molecular collisions human enzymes = ___°- ____°C body temp = ____°C __________: increase beyond optimum T° increased energy level of molecules disrupts bonds in enzyme & between enzyme & substrate H, ionic = weak bonds ________________ = lose 3D shape (3° structure) ________: decrease T° molecules move ______________ ________ collisions between enzyme & substrate
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Enzymes and temperature
Different enzymes function in different organisms in different environments hot spring bacteria enzyme human enzyme 37°C 70°C reaction rate temperature (158°F)
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How do ectotherms do it? Enzymes work within narrow temperature ranges. Ectotherms, like snakes, do not use their metabolism extensively to regulate body temperature. Their body temperature is significantly influenced by environmental temperature. Desert reptiles can experience body temperature fluctuations of ~40°C (that’s a ~100°F span!). What mechanism has evolved to allow their metabolic pathways to continue to function across that wide temperature span?
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pH pepsin trypsin reaction rate pH 1 2 3 4 5 6 7 8 9 10 11 12 13 14
What’s happening here?! pepsin trypsin pepsin reaction rate trypsin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH
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Factors affecting enzyme function
______ changes in pH adds or remove ______ disrupts bonds, disrupts 3D shape disrupts attractions between charged amino acids affect 2° & 3° structure _______________________ protein optimal pH? most human enzymes = pH __-____ depends on localized conditions _________ (stomach) = pH __-___ _________ (small intestines) = pH __ 7 2 1 3 4 5 6 8 9 10 11
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Salinity What’s happening here?! reaction rate salt concentration
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Factors affecting enzyme function
____________ concentration changes in salinity adds or removes cations (+) & anions (–) disrupts bonds, disrupts 3D shape disrupts attractions between charged amino acids affect 2° & 3° structure ______________________________ protein enzymes intolerant of extreme salinity Dead Sea is called dead for a reason!
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Compounds which _______ enzymes
Fe in hemoglobin _____________ ________________ non-protein, small __________ compounds & ions Mg, K, Ca, Zn, Fe, Cu bound within enzyme molecule _________________ non-protein, _________ molecules bind temporarily or permanently to enzyme near active site many vitamins ______ (niacin; B3) ______ (riboflavin; B2) _________________________ Hemoglobin is aided by Fe Chlorophyll is aided by Mg Mg in chlorophyll
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Compounds which ________ enzymes
___________________ molecules that _________ enzyme activity competitive inhibition noncompetitive inhibition irreversible inhibition feedback inhibition
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Competitive Inhibitor
Inhibitor & substrate “compete” for __________ 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 ___________ concentration saturate solution with substrate so it out-competes inhibitor for active site on enzyme Ethanol is metabolized in the body by oxidation to acetaldehyde, which is in turn further oxidized to acetic acid by aldehyde oxidase enzymes. Normally, the second reaction is rapid so that acetaldehyde does not accumulate in the body. A drug, disulfiram (Antabuse) inhibits the aldehyde oxidase which causes the accumulation of acetaldehyde with subsequent unpleasant side-effects of nausea and vomiting. This drug is sometimes used to help people overcome the drinking habit. Methanol (wood alcohol) poisoning occurs because methanol is oxidized to formaldehyde and formic acid which attack the optic nerve causing blindness. Ethanol is given as an antidote for methanol poisoning because ethanol competitively inhibits the oxidation of methanol. Ethanol is oxidized in preference to methanol and consequently, the oxidation of methanol is slowed down so that the toxic by-products do not have a chance to accumulate.
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______-Competitive Inhibitor
Inhibitor binds to site other than active site ______________ inhibitor binds to _____________ site causes enzyme to change ___________ conformational change ________ 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 Basis of most chemotherapytreatments is enzyme inhibition. Many health disorders can be controlled, in principle, by inhibiting selected enzymes. Two examples include methotrexate and FdUMP, common anticancer drugs which inhibit enzymes involved in the synthesis of thymidine and hence DNA. Since many enzymes contain sulfhydral (-SH), alcohol, or acid groups as part of their active sites, any chemical which can react with them acts as a noncompetitive inhibitor. Heavy metals such as silver (Ag+), mercury (Hg2+), lead ( Pb2+) have strong affinities for -SH groups. Cyanide combines with the copper prosthetic groups of the enzyme cytochrome C oxidase, thus inhibiting respiration which causes an organism to run out of ATP (energy) Oxalic and citric acid inhibit blood clotting by forming complexes with calcium ions necessary for the enzyme metal ion activator.
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Irreversible inhibition
Inhibitor ___________ binds to enzyme competitor permanently binds to _______ site allosteric permanently binds to ___________ site permanently changes shape of enzyme _________ gas, ________, many insecticides (malathion, parathion…) cholinesterase inhibitors doesn’t breakdown the neurotransmitter, acetylcholine Another example of irreversible inhibition is provided by the nerve gas diisopropylfluorophosphate (DFP) designed for use in warfare. It combines with the amino acid serine (contains the –SH group) at the active site of the enzyme acetylcholinesterase. The enzyme deactivates the neurotransmitter acetylcholine. Neurotransmitters are needed to continue the passage of nerve impulses from one neurone to another across the synapse. Once the impulse has been transmitted, acetylcholinesterase functions to deactivate the acetycholine almost immediately by breaking it down. If the enzyme is inhibited, acetylcholine accumulates and nerve impulses cannot be stopped, causing prolonged muscle contration. Paralysis occurs and death may result since the respiratory muscles are affected. Some insecticides currently in use, including those known as organophosphates (e.g. parathion), have a similar effect on insects, and can also cause harm to nervous and muscular system of humans who are overexposed to them.
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Allosteric _______________
Conformational changes by regulatory molecules inhibitors keeps enzyme in inactive form activators keeps enzyme in active form Conformational changes Allosteric regulation
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Metabolic pathways A B C D E F G A B C D E F G
enzyme 1 enzyme 3 enzyme 2 enzyme enzyme 4 enzyme 5 enzyme 6 Chemical reactions of life are organized in pathways divide chemical reaction into many small ________ artifact of ______________ __ efficiency intermediate branching points __ control = regulation
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Whoa! All that going on in those little mitochondria!
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!
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___________________________
Regulation & coordination of production product is used by next step in pathway final _________ is ___________ of ________ step ____________ inhibitor of earlier enzyme feedback inhibition no unnecessary accumulation of product!! A B C D E F G enzyme 1 enzyme 2 enzyme 3 enzyme 4 enzyme 5 enzyme 6 X allosteric inhibitor of enzyme 1
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Feedback inhibition Example
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 isoleucine
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