Enzymes 2 Flashcards
<p>Give an example of two enzymes that catalyse the same reaction?</p>
<p>Glucokinase and hexokinase</p>
<p>What reaction to glucokinase and hexokinase catalyse?</p>
<p>Glucose + ATP→ Glucose-6-phosphate + ADP</p>
<p>Where is glucokinase found?</p>
<p>In the liver</p>
<p></p>
<p>Where is hexokinase found?</p>
<p>Everywhere other than the liver</p>
What kinetic properties do glucokinase and hexokinase have (KM and vmax)
<p>What does a graph of the activity of glucokinase and hexokinase look like and explain it?</p>
<p>Hexokinase is constantly working flat out whereas glucokinase can respond proportionally to blood glucose</p>
<p>Why does hexokinase have a low KM?</p>
<p>So it can respond proportionally to blood glucose</p>
<p>When [glucose] is low you don't want the liver to break it down as you want it to be released into the blood</p>
<p>What is the difference between glucose-6-phosphate and glucose?</p>
<p>G-6-P cannot leave the cell</p>
<p>What do enzymes being found where they shouldn't be indicate?</p>
<p>Tissue damage, enzymes may escape from damaged cells</p>
<p>How is enzyme activity measured in clinical scenarioes?</p>
<p>With an arbitory value</p>
<p>1U/ml o 100% = normal</p>
<p>What is an isozyme?</p>
<p>Different enzymes that catalyse the same reaction</p>
<p>Where are isoenzymes often found relative to each other?</p>
<p>In different tissues</p>
<p>Are isoenzymes coded for by the same gene?</p>
<p>No, they are products of different genes</p>
<p>What is electrophoresis?</p>
<p>Process where you can seperate out biological molecules</p>
<p>How does electrophoresis work?</p>
<p>Larger molecules get stuck and so move less than smaller molecules, charge also has an impact</p>
<p>What is creatine kinase (CK)?</p>
<p>An example of an isoenzyme which is a dimer made up from two polypeptide chains B and M</p>
<p>What is a dimer?</p>
<p>Oligomer consisting of two monomers joined by bonds that can be strong or weak, covalent or intermolecular</p>
<p>What is an oligomer?</p>
<p>Molecule complex of chemicals that consists of a few monomer units</p>
<p>What are the 3 isomorms that creatine kinase (CK) can form?</p>
<p>CK1 (BB)</p>
<p>CK2 (BM)</p>
<p>CK3 (MM)</p>
<p>How are enzymes used in diagnosis?</p>
<p>Measure activity and compare with normal</p>
<p>Sepperate differnt forms of enzymes by electrophoresis</p>
<p>Are enzymes restricted to interacting with one substance?</p>
<p>No, most enzymes can interact with a variety of substances</p>
<p>How does the KMvary between enzymes and their different substrates?</p>
<p>Changes for each substrate</p>
<p>What does catalysing a reaction with two or more substances normally involve?</p>
<p>The transfer of groups from one to the other</p>
<p>What ways can the catalyse of two or more substances with the transfer of groups occur?</p>
<p>Random order or ordered with ternary complex</p>
<p>No ternary complex formation</p>
What does a random order reaction involving a ternary complex look like?
What does an ordered reaction involving a ternary complex look like?
With does a reaction with no formation of a ternary complex look like?
<p>What is an example of an enzyme that uses an ordered sequential mechanism?</p>
<p>Lactate dehydrogenase for the reaction of pyruvate to lactate</p>
<p>What is an example of an enzyme that uses a random sequential mechanism?</p>
<p>Creatine kinase (CK) for creatine to phosphocreatine</p>
<p>What do ordered and unordered squential mechanisms have in common?</p>
<p>The ternary complex is formed first</p>
<p>What is an example of an enzyme that uses a no formation of tertary complex mechanism?</p>
<p>Asparate aminotransferase, uses a double displacement reaction</p>
<p>What is a double displacement reaction?</p>
<p>Substrates bounce on and off the enzyme</p>
<p>What happens when you take an amino group of an amino acid?</p>
<p>It becomes a ketoacid</p>
<p>What notation is commonly used to show the mechanisms of enzyme reactions?</p>
<p>Clelend notation</p>
<p>What is an allosteric enzyme?</p>
<p>Enzymes made up of many subunits</p>
<p>What sites are on an allosteric enzyme?</p>
<p>Can contain many active sites, they have other sites that can be used for regulation</p>
<p>What do the kinetics of an allosteric enzyme look like and why is this?</p>
<p>Because of cooperative binding</p>
<p>What is cooperative binding?</p>
<p>One substance binds to an enzyme subunit causing a change in the acitve site of other sub units</p>
<p>What is an example of an enzyme that uses cooperative binding?</p>
<p>Haemoglobin</p>
<p>What factors affect the way that enzymes function?</p>
<p>Temperature</p>
<p>pH</p>
<p>Inhibition</p>
<p>How does temperature affect enzyme functionality?</p>
<p>As temperature increases, molecule collisions increase</p>
<p>As temperature increases, internal energy of molecule increases</p>
<p>If temperature increases further the enzyme will denature</p>
<p>How does pH affect enzyme functionality?</p>
<p>Changes charge of amino acids</p>
<p>If the active amino acids change charge will stop working</p>
<p>Extreme pH will denature the enzyme</p>
<p>Also affects substrates</p>
<p>What are the three types of inhibitors?</p>
<p>Competative inhibitor</p>
<p>Non-competative inhibitor</p>
<p>Uncompetative inhibitor</p>
<p>What is a competative inhibitor?</p>
<p>Binds to the active site non covalently, competing with the substrate</p>
<p>What do competative enzymes cause in terms of enzyme kinetics?</p>
<p>Decreased affinity (KMincrease)</p>
<p>vmaxremains the same as increasing [substrate] can overcome it</p>
<p>What does the best inhibitor look like and why?</p>
<p>The transition state because it binds better</p>
<p>Why are there not a lot of transition state drugs?</p>
<p>The transition state is hard to determine</p>
<p>What are non-competative inhibitors?</p>
<p>Bind to somewhere other than the active site non covalently</p>
<p>What do non-competative inhibitors cause in terms of enzyme kinetics?</p>
<p>KMunchanged as substrate can still bind</p>
<p>vmaxdecreases because cannot out compete the inhibitor</p>
What do inhibitors on a Lineweaver-Burk plot look like?
<p>What is an example of an irreversible inhibitor?</p>
<p>Cyanide (CN-)</p>
<p>What does biological reactions occuring in pathways allow?</p>
<p>Regulation of a key step byt regulating the enzyme, often the first step</p>
<p>What are the 2 main ways of regulating enzymes?</p>
<p>Allosteric enzymes</p>
<p>Covalently modified enzymes</p>
<p>What is feedback inhibition?</p>
<p>Build up of an end product inhibits an earlier enzyme</p>
<p>What kind of inhibition do pathways often use?</p>
<p>Feedback inhibition</p>
<p>What are allosteric effectors?</p>
<p>Cell metabolites that bind non covalently to a site on the enzyme that is not the active site</p>
<p>What do effectors do to an enzyme structure?</p>
<p>Cause it to change</p>
<p>What are the two types of effectors?</p>
<p>Inhibitor</p>
<p>Activator</p>
<p>What two models explain allosteric kinetics?</p>
<p>Concerted model</p>
<p>Sequential model</p>
<p>What does the concerted model state?</p>
<p>Sub units exist in two conformations (one binds well and the other doesn't)</p>
<p>With no substance the enzyme flips between the two conformations</p>
<p>All sub units must be in the same conformation (flip in concert)</p>
<p>What are allosteric activators?</p>
<p>Bind somewhere other than the active site, locking the open conformation</p>
<p>What are allosteric inhibitors?</p>
<p>Bind somewhere other than the active site, locking in the closed conformation</p>
<p>What are the properties of the sequential model?</p>
<p>Substrate binding causes a change in one subunit</p>
<p>Binding causes conformational change</p>
<p>What is an example of a reversible covalent modificaiton that can inhibit an enzyme?</p>
<p>Being phosphorylated</p>
<p>What are the two kinds of enzymes that catalyse the phosphorylation of an enzyme?</p>
<p>Protein kinases (adds phosphory group to a protein)</p>
<p>Protein phophotases (removes phosphoryl group)</p>
<p>What do multiple phosphorylation sites allow?</p>
<p>Fine control of an enzymes function, it is never completely off or on but is finely tuned</p>
<p>What is a proprotein?</p>
<p>Enzymes existing as an inactive precurser protein</p>
<p>What happens when the proprotein is cleaved of an enzyme?</p>
<p>Enzyme becomes active by proteases</p>
<p>What kinds of enzymes often use proprotein for regulation?</p>
<p>Digestive enzymes</p>
<p>What is proteolysis?</p>
<p>Process of breaking peptide bonds between amino acids</p>
<p>What is a protease?</p>
<p>Enzymes that perform proeolysis (protein catabolism by hydrolysis of peptide bonds)</p>
