Hemoglobin T and R States Quiz
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Questions and Answers

Which transition metal binds well to O2 but would generate free radicals if free in solution?

  • Magnesium (Mg)
  • Iron (Fe+) (correct)
  • Zinc (Zn)
  • Copper (Cu)
  • What evolutionary solution is mentioned for capturing the oxygen molecule safely?

  • Directly binding oxygen with protein side chains
  • Binding oxygen with heme that is protein bound (correct)
  • Using free Fe2+ ions
  • Utilizing organometallic compounds like Fe3+
  • Which type of structure is myoglobin?

  • Lipid structure
  • Nucleic acid structure
  • Carbohydrate structure
  • Protein structure (correct)
  • What is the role of the 'proximal' His in myoglobin structure?

    <p>It coordinates directly with Fe</p> Signup and view all the answers

    Why does CO bind better to free heme than O2?

    <p>Similar size and shape to O2</p> Signup and view all the answers

    What factor contributes to CO binding about 200x less effectively than O2 in the middle of the protein?

    <p>Presence of a distal His residue</p> Signup and view all the answers

    How does protein structure affect ligand binding?

    <p>By having a complementary binding site for the ligand</p> Signup and view all the answers

    What is one reason why lowering the affinity (P50) of myoglobin to oxygen would not help in delivering oxygen to tissues?

    <p>It results in too much oxygen bound in the lungs</p> Signup and view all the answers

    What is the consequence of the formation of a carbamate in hemoglobin?

    <p>Stabilization of the T state</p> Signup and view all the answers

    What distinguishes hemoglobin from myoglobin in terms of oxygen binding?

    <p>Hemoglobin binds oxygen cooperatively, myoglobin does not</p> Signup and view all the answers

    Which factor leads to the release of oxygen in the tissues?

    <p>Protonation of His146</p> Signup and view all the answers

    What is required for positive cooperativity in hemoglobin's affinity for oxygen?

    <p>Quaternary structure with multiple subunits</p> Signup and view all the answers

    What role does H+ play in oxygen transport by hemoglobin?

    <p>Leads to oxygen release in tissues</p> Signup and view all the answers

    What does a sigmoidal binding curve indicate in terms of ligand cooperativity?

    <p>Positive cooperativity</p> Signup and view all the answers

    What is the quantitative description of cooperativity represented by in a Hill plot?

    <p>$Ka = n \times Ka$</p> Signup and view all the answers

    How does a drop in pH affect hemoglobin's affinity for oxygen?

    <p>Decreases affinity for oxygen</p> Signup and view all the answers

    What contributes to the efficiency of oxygen transport in the body?

    <p>pH difference between lungs and metabolic tissues</p> Signup and view all the answers

    What percentage of carbon dioxide is exported in the form of a carbamate on the amino terminal residues of hemoglobin subunits?

    <p>15-20%</p> Signup and view all the answers

    What does a small equilibrium dissociation constant (Kd) indicate?

    <p>High affinity</p> Signup and view all the answers

    Which of the following is NOT a component of a heme group?

    <p>Sulfur atom</p> Signup and view all the answers

    What characterizes the specificity of proteins in binding to ligands?

    <p>Complementary size, shape, charge, or hydrophobic/hydrophilic character</p> Signup and view all the answers

    Which type of proteins undergo conformational changes upon ligand binding, allowing for tighter binding?

    <p>Globins</p> Signup and view all the answers

    How is the equilibrium composition characterized in terms of the equilibrium constant Ka?

    <p>[P]<em>[L] = Ka</em>[PL]</p> Signup and view all the answers

    What does the heme-bound FE cation represent in myoglobin?

    <p>+2 (reduced) state</p> Signup and view all the answers

    What triggers the conformational change from the T to R state in hemoglobin?

    <p>Breaking of ion pairs between the α1-B2 interface</p> Signup and view all the answers

    Which state of hemoglobin has a higher affinity for oxygen?

    <p>R state (Relaxed state)</p> Signup and view all the answers

    What does the binding of O2 cause in the hemoglobin subunits?

    <p>Slide of ab pairs past each other and rotation</p> Signup and view all the answers

    Who determined the structures of hemoglobin in the presence and absence of Oxygen?

    <p>Max Perutz</p> Signup and view all the answers

    What is hypothesized to cause the significant conformational change in hemoglobin upon Oxygen binding?

    <p>Shift in iron's position in the Heme</p> Signup and view all the answers

    What does the binding of O2 in the hemoglobin subunit's pocket trigger?

    <p>Localized movement of the proximal His and cascade of movements throughout the subunit</p> Signup and view all the answers

    What does Linus Pauling discover that helps lower the standard state free energy change of a reaction?

    <p>Transition state stabilization</p> Signup and view all the answers

    In enzymatic catalysis, what is the role of the catalytic triad in chymotrypsin?

    <p>To stabilize the acyl-enzyme intermediate</p> Signup and view all the answers

    What is the function of the acyl-enzyme intermediate in enzymatic reactions?

    <p>To lower the activation barrier for the reaction</p> Signup and view all the answers

    How does the catalytic triad in chymotrypsin contribute to the catalytic mechanism of the enzyme?

    <p>By stabilizing the transition state of the reaction</p> Signup and view all the answers

    Which of the following is a key feature of peptide bond formation catalyzed by enzymes like chymotrypsin?

    <p>Stabilization of the transition state</p> Signup and view all the answers

    What is the primary function of water activation in enzymatic reactions like those catalyzed by chymotrypsin?

    <p>To provide nucleophiles for reaction mechanisms</p> Signup and view all the answers

    What is the role of Asp-102 in the catalytic triad of chymotrypsin?

    <p>Deactivates water for nucleophilic attack by Ser-195</p> Signup and view all the answers

    What does Ser-195 do in the catalytic triad of chymotrypsin?

    <p>Nucleophilically attacks the carbonyl carbon of the substrate</p> Signup and view all the answers

    Why does His-57 interact with Serine in chymotrypsin catalysis?

    <p>To transform Serine into a better nucleophile</p> Signup and view all the answers

    In chymotrypsin catalysis, what is the function of the catalytic triad in breaking peptide bonds?

    <p>Activating the water molecule for nucleophilic attack</p> Signup and view all the answers

    Which statement accurately describes the oxyanion hole in chymotrypsin?

    <p>It stabilizes the transition state of peptide bond formation</p> Signup and view all the answers

    What is the main function of the acyl-enzyme intermediate in chymotrypsin catalysis?

    <p>Further stabilize the enzyme-substrate complex</p> Signup and view all the answers

    What is the primary function of a Lewis base?

    <p>Donating electrons</p> Signup and view all the answers

    In acid-base catalysis, what role does water typically play?

    <p>Acting as both an acid and a base</p> Signup and view all the answers

    Why might general acid-base catalysis be preferred over specific acid-base catalysis?

    <p>General catalysis is more efficient</p> Signup and view all the answers

    Which amino acid side chain is not usually ionizable and involved in general acid-base catalysis?

    <p>Serine</p> Signup and view all the answers

    What is the main requirement for general acid-base catalysis when proton transfer from water is slow?

    <p>Presence of another proton donor or acceptor</p> Signup and view all the answers

    What is the role of histidine in the catalytic triad of chymotrypsin?

    <p>Removal of proton from serine for nucleophilic attack</p> Signup and view all the answers

    In enzyme catalysis, what is the purpose of the amino acid group in general acid-base catalysis?

    <p>Neutralizing charges on intermediates</p> Signup and view all the answers

    What is the function of the aspartate residue in chymotrypsin's active site?

    <p>Stabilization of the acyl-enzyme intermediate</p> Signup and view all the answers

    What occurs during the burst phase in chymotrypsin catalysis?

    <p>Release of p-nitrophenol</p> Signup and view all the answers

    What is the purpose of water activation in chymotrypsin catalysis?

    <p>Formation of the acyl-enzyme intermediate</p> Signup and view all the answers

    Which residue in chymotrypsin is responsible for stabilizing the transition state during catalysis?

    <p>Aspartate</p> Signup and view all the answers

    What effect does His have on water molecules during chymotrypsin catalysis?

    <p>Removal of protons to activate water for nucleophilic attack</p> Signup and view all the answers

    How do general acids and bases help increase the rate of a reaction in enzyme catalysis?

    <p>Avoid the need for extremely high or low pH values</p> Signup and view all the answers

    What is one role of covalent catalysis in enzyme catalysis?

    <p>Make transient covalent bonds between the enzyme and substrate</p> Signup and view all the answers

    What amino acids can act as nucleophiles involved in covalent catalysis?

    <p>Serine, thiolate, amine</p> Signup and view all the answers

    In chymotrypsin, what accelerates peptide bond hydrolysis?

    <p>Metal ion catalysis</p> Signup and view all the answers

    What is the role of the catalytic triad in chymotrypsin for peptide bond hydrolysis?

    <p>Creates a negative charge to stabilize intermediates</p> Signup and view all the answers

    How does acyl-enzyme intermediate formation contribute to enzyme catalysis?

    <p>Facilitates the transfer of acyl groups</p> Signup and view all the answers

    What does the turnover number, kcat, represent?

    <p>The number of substrate molecules converted per unit time by one enzyme molecule</p> Signup and view all the answers

    What is the approximate measure of substrate's affinity for enzyme known as?

    <p>Km</p> Signup and view all the answers

    Why is Km often compared to Kd?

    <p>To assess the balance between breakdown and formation of ES complex</p> Signup and view all the answers

    Which enzyme has a turnover number of approximately 40 million per second?

    <p>Catalase</p> Signup and view all the answers

    What is the significance of a lower Km value in enzyme kinetics?

    <p>Higher rate of enzymatic reaction</p> Signup and view all the answers

    In enzyme kinetics, what does Kcat measure?

    <p>[S] at ½ Vmax</p> Signup and view all the answers

    Which assumption underlies the comparison between Km and Kd?

    <p>[ES] formation is faster than ES breakdown</p> Signup and view all the answers

    What does Km represent in terms of substrate concentration and enzymatic reaction?

    <p>[S] at which half-maximal velocity is achieved</p> Signup and view all the answers

    What are the factors that can affect the rate of an enzymatic reaction?

    <p>Enzyme concentration, substrate availability, temperature</p> Signup and view all the answers

    What is the primary purpose of studying enzyme kinetics?

    <p>To understand the rate of enzymatic reactions</p> Signup and view all the answers

    In enzyme assay example with Alcohol Dehydrogenase (ADH), why is NADH production monitored at 340 nm?

    <p>NADH has a higher absorbance at 340 nm than NAD-</p> Signup and view all the answers

    What does the process of making mutations in enzymes aim to determine?

    <p>Essential amino acids for enzyme activity</p> Signup and view all the answers

    How are kinetic parameters determined in enzyme kinetics studies?

    <p>By repeating experiments under different conditions</p> Signup and view all the answers

    What is one of the reasons for differentiating residues involved in catalysis from those involved in substrate binding?

    <p>To understand the enzyme's mechanism of action</p> Signup and view all the answers

    Why is it important to understand the regulation of enzyme activity?

    <p>To control the rate of enzymatic reactions</p> Signup and view all the answers

    What does the study of enzyme kinetics provide in terms of biocatalysis?

    <p>Precise quantitative descriptions of biocatalysis</p> Signup and view all the answers

    What is the effect of increasing substrate concentration on the initial velocity of an enzymatic reaction?

    <p>Initial velocity increases</p> Signup and view all the answers

    Which enzyme relationship is represented by a hyperbolic curve when plotting initial velocity against substrate concentration?

    <p>Michaelis-Menten Enzymes</p> Signup and view all the answers

    What is the equation that explains the hyperbolic curve observed when plotting initial velocity versus substrate concentration?

    <p>Y is Vo, Vmax is asymptote, X is [S], Km is [S] when Vo is ½ Vmax</p> Signup and view all the answers

    What does steady state condition mean in enzyme kinetics?

    <p>[ES] formation equals [ES] breakdown</p> Signup and view all the answers

    Which assumptions allowed Michaelis and Menten to derive an equation fitting the hyperbolic curve in enzymatic reactions?

    <p>k1 and k2 are rate limiting, [P] and [ES] are negligible, and [Efree] = [ET] - [ES]</p> Signup and view all the answers

    In Michaelis-Menten kinetics, what does Km represent?

    <p>[S] when Vo is half of Vmax</p> Signup and view all the answers

    What does Vmax represent in Michaelis-Menten kinetics?

    <p>[E] at maximum velocity</p> Signup and view all the answers

    Under steady-state conditions in enzyme kinetics, what does d[ES]/dT equal?

    <p>0</p> Signup and view all the answers

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