BCHM 307 1st Edition Lecture 14Outline of Last Lecture I. Km and VelocityA. Velocity EquationII. Allosteric Enzyme ReactionsA. Sigmoidal CurveB. Allosteric Chain ReactionIII. Enzyme Kinetics GraphA. How to Plot the GraphB. Reverse ReactionOutline of Current Lecture I. Lineweaver-Burk PlotII. Enzyme InhibitorsA. Irreversible InhibitorsIII. Reversible InhibitorsA. Competitive InhibitorsB. Non-Competitive InhibitorsC. Un-Competitive InhibitorsIV. How Enzyme Catalysis WorksCurrent LectureThe Michaelis-Menton graph will not allow you to properly estimate Km or Vmax, due to its curved shape. The graph can be turned into a linear form that will give you the true values of Km and Vmax. This transformed graph is called the Lineweaver-Burk plot or double reciprocal plot. The graph plots 1/velocity versus 1/substrate concentration. The line plotted has the standard line form of y=mx + b. The slope is given by Km/Vmax. The y-intercept is 1/Vmax and the x-intercept is -1/Km.Enzyme inhibitors are molecules that decrease the catalysis rate. Enzyme inhibitors can be broken down into two categories: reversible and irreversible. Irreversible inhibitors are also called suicide inhibitors. They covalently attach to the enzyme and completely inactivate it. They can’t inhibit another enzyme once attached though. The covalent bond will modify the enzyme, causing it to no longer by a catalyst. This permanently modified enzyme is called a derivitized enzyme. An example would be organoflurophosphates, such as DIFP. DIFP inhibits acetylcholinesterase and bonds with the serine residues in the active site. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Reversible inhibitors can be broken down into three groups: competitive, non-competitive, and un-competitive. Competitive inhibitors bind to and block the enzyme’s active site temporarily. The inhibitor looks very similar to the substrate, allowing it to fit closely to the active site though not perfectly. The Km will increase when this happens, while the Vmax will stay the same. This decreases the affinity of the substrate for the enzyme overall. Increasing the substrate concentration will help to overcome these effects. An example is malonate, which is a competitive inhibitor of succinate dehydrogenase. Atropine is another example, which helps to break down acetylcholine to prevent chronic nerve stimulation.Nom-competitive inhibitors bind to another area on the enzyme, besides the active site. These inhibitors do not resemble the substrates. In terms of enzyme kinetics, the Km will say the same due to the inhibitor not binding to the active site. The Vmax will decrease though. Increasing the substrate concentration will not help to overcome these effects.Uncompetitive inhibitors can only bind to the enzyme, at a place other than the active site, when the substrate is already bound to the enzyme. The Km will decrease, increasing the substrate concentration will not effect this either.Certain functional groups are involved in enzyme catalysis. Alpha amino and carboxyl groups cannot be involved, because they are involved in peptide bonds. Specific R groups are involved in catalysis, including those of: Asp, Glu, His, Lys, Ser, Cys, and Tyr. When an inhibitor covalently binds to the enzyme, it also binds to the active site amino acid residues. This helps biochemists to understand what kind of chemistry is
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