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Lecture 10

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BIOL 1000
Michael Gadsden

Lecture 10 Energy and Enzymes  Mainly in Chapter 4 Energy  Free Energy (ΔG) – portion of a systems energy available to do work o Takes entropy and enthalpy into account o ΔG = Enthalpy + Entropy o Enthalpy – Heat or radiation transfer (H)  ΔH – Change of enthalpy  Enthalpy of Products – Enthalpy of reactants PROD- HREACT  If ΔH < 0 – Exothermic, favoured reaction (should go that way)  If ΔH > 0 – Endothermic, non-favoured reaction (shouldn’t go that way, requires energy input [usually in form of heat]) o Entropy – Randomness is favoured over order (S)  i.e. More free molecules in a system  Favoured state is the state with more free molecules  2 TNT 15 Product Molecules  Therefore the 15 product molecules favoured because 15 > 2  Releases lots of energy  ΔS = SProd React o Exergonic reactions release heat energy (ΔG < 0) o Endergonic take in heat energy (ΔG > 0)  See sheet for diagrams  NB: Opposite reactions of endergonic vs. exergonic have the same magnitude, different sign (Like Newton’s Third...) o Endergonic reactiona usually coupled to exergonic reactions Metabolic Pathways  Catabolic breaks down complex molecules  Anabolic build up complex molecules Enzymes  Enzymes are catalysts that reduce the value of activation energy (energy needed to start a reaction)  Enzymes bring molecules in a specific position that will change them up by making them react with certain AA’s and leave differently  Work best at certain conditions o Pepsin is a low pH because it’s in the stomach o Need things like heat, pH  If not perfect, the protein’s shape is changed o Cofactors needed sometimes too  Fe, Mg (inorganic materials)  These stabalize molecules, transfer electrons  Iron for example does this in the ETC  Organic factors are called “coenzymes”  Help as donors of something (redox etc.)  Example of this would Folic Acids that donate methyl  Haemoglobin needs Fe as a cofactor (carries 2 in the blood)  Enzymes in the ETC need this too Active Site  Numbers on things like “GLU 35” mean what number in the primary sequence  NB : DNA and RNA have tertiary structures  The “Enzyme Intermediate” (EI) state is unstable  The glycosidic bond (α-Form) has been hydrolyzed Lowering Activation Energy  Localizing reactants (two molecules must be put together perfectly [like two people being PUT shoulder to shoulder]) o Enzymes localize and orient reactants to be in the perfect state  Move e , H or both o Take protons off of certain areas so that water or anything else can more easily access where it needs to be accessed (leaves less to randomness)  Bond Stress o Bending molecules so that electrons are easier to break Enzymes in Extreme Conditions  Enzymes that can survive and work optimally at extreme conditions o o T. Aq. In 72 C o It’s DNA Polymerase in Polymerase Chain Reaction (PCR) is used for forensics, disease identification where DNA Replication (in the lab) is done at high temperatures  High temps used to make much more DNA than is available at that time o DNA Polymerase is called “TAQ Polymerase” o PCR (Basics!)  Heat to denature DNA (95 C) o  Prime DNA to prepare the DNA Polymerase (60 C)  Replicate DNA (72 C)  Repeats 30 times!  If one starts with 1 DNA molecule, they end up with 2 = Approx 10  Note, in reality about 40 template molecules are required for this to succeed. Kinetics  The rate of reaction – how fast a product is made o Rate = # Products Made / # Enzyme Molecules / Time = Velocity (V)  Saturation level is when the rate of reaction is at its maximumMAXV o All enzymes are complexed with substrate, cannot do much more o As more substrate added, more product is made untilMAX attained, where a plateau occurs o AT ½ VMAX – Substrate [] is callMd K (the Michaelis – Menton Constant)  This is a characteristic for all enzyme substrate pairs  Different for all enzymes (indicates efficiency)  Lower K M Higher Efficiency because this means it can reach itMAXearlier! Alcohol  Alcohol  Aldehyde (via Alcohol Dehydrogenase) ADH o Different people have different booze control because of tMe K value for their personal ADH  Aldehyde  Acetate (Aldehyde Dehydrogenase)  Disulfiram  Irreversible deactivates ALDH o This makes you build up aldehyde quickly so it makes you have hangover symptoms quicker Inhibition  Competitive Inhibition o Inhibitor and substrate compete for active site o Suicide inhibitors become irreversibly changed (can be overcome) [Covalent Bond] o KMincreases with the competitive inhibitors o Viagara  High cGMP leads to reduction of Ca+ 2+  cGMP phosphodiesterase  increased Ca  Vascular Muscle Contraction  Pharm companies looked for PDE (phosphodiesterase) inhibitors to lessen constriction and blood pressure  Viagara was designed to do this  In Males, it inhbited PDE in penile vascular muscle  increased blood flow o Isoforms/Isozymes – enzymes perform same catalytic function but usually made from different genes and thus significantly different primary sequences of amino acids  Different genes arisen from duplication?  I.e. 75% similarity : 25% different amino acids  See sheet for drawing  Isozymes usually expressed in different tissues (different copies do things in different places (PDE in penis vs. rest of body)  One can determine different tissue damage by the isozymes released in the blood (i.e. looking for this after a heart attack) o Allozymes – KNOW THIS  Locus – region on a chromosome/genome (particular spot)  See sheet  Genetic sequence should be the same or nearly the same on each locus  i.e. the same gene but the sequences may differ slightly (may not)  Each version of the genetic region/sequence at a locus is called an ALLELE  Allele – different versions/copies of same genetic sequence  Thus an allozyme is a different form of an enzyme that are encoded at the same locus but from either:  Different alleles (One allele codes for one part of the enzyme)  Different processing of the enzyme in different tissue (Which how the exons are put together) o Examples – Sulfa  PABA – Para Amino Benzolic Acid  These drugs inhibit the creation of Dihydrofolic acid in bacteria = good for us  Trimethoprim inhibits dihydrofolate reductase (bacterial form as well) o Example – Lactate Dehydrogenase  A tetramer (four polypeptides make the 4 structure) o o Only active during 4 structure o Adult all M , child all H 4 4  Non-Competitive Inhibition o Inhibitor binds allosterically (at site 2, not the active site) o With the inhibitor there, the substrate cannot bind o V cannot be reached by dilution, it cannot be reached at all!
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