Biochemistry: Enzyme Coordination and Interactions
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Questions and Answers

Which amino acid is considered the least hydrophobic among hydrophobic amino acids?

  • Glycine (correct)
  • Isoleucine
  • Proline
  • Phenylalanine

    • What characteristic of proline differentiates it from other amino acids?

  • It can form disulfide bonds.
  • It contains a primary amine.
  • It contains a secondary amine. (correct)
  • It has multiple chiral centers.

    • Which amino acid can form disulfide bonds?

  • Tyrosine
  • Cysteine (correct)
  • Phenylalanine
  • Tryptophan

    • At pH 7.0, which property is indicative of polar amino acids?

    <p>They have side chains with electronegative atoms.</p> Signup and view all the answers

    Which hydrophobic amino acid absorbs UV light at approximately 280 nm?

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

    Which of the following amino acids has a polar side chain?

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

    Which statement is true about aromatic amino acids?

    <p>Tryptophan is less hydrophobic than phenylalanine.</p> Signup and view all the answers

    What is the principal factor allowing the diverse functions of proteins?

    <p>Variability in side chains</p> Signup and view all the answers

    What is the primary purpose of the citric acid cycle in metabolism?

    <p>To oxidize acetyl-CoA for energy production</p> Signup and view all the answers

    Which metabolic pathway directly leads to the conversion of glucose into ATP?

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

    Which of the following interactions is critical for the stability of biological molecules?

    <p>Both covalent bonds and noncovalent interactions</p> Signup and view all the answers

    What role do enzymes play in metabolic pathways?

    <p>Enzymes regulate and facilitate metabolic reactions</p> Signup and view all the answers

    Which process involves the formation of glucose from non-carbohydrate sources?

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

    Which of the following best describes oxidative phosphorylation?

    <p>A stage where ATP is synthesized through an electron transport chain</p> Signup and view all the answers

    What is the main function of glycogen metabolism?

    <p>To convert glycogen back to glucose for energy</p> Signup and view all the answers

    Which strategy is employed to regulate enzyme activity in metabolic pathways?

    <p>Feedback inhibition</p> Signup and view all the answers

    What do electrostatic interactions primarily involve?

    <p>Interactions between charged groups forming a salt bridge</p> Signup and view all the answers

    Which law describes the force between two charged particles?

    <p>Coulomb's Law</p> Signup and view all the answers

    What is the bond energy of singly charged ions separated by 3Å in water?

    <p>5.8 kJ/mol</p> Signup and view all the answers

    How do van der Waals interactions primarily behave at longer distances?

    <p>Attraction dominates the interaction</p> Signup and view all the answers

    What characterizes London dispersion forces?

    <p>They result from transient electronic asymmetries.</p> Signup and view all the answers

    Hydrophobic interactions occur in water primarily due to what reason?

    <p>Nonpolar molecules aggregate in a polar solvent</p> Signup and view all the answers

    What does the repulsive component of van der Waals interactions depend on?

    <p>Electron-electron repulsion at small distances</p> Signup and view all the answers

    Which of the following statements about electrostatic interactions is false?

    <p>Their strength is constant regardless of species nature.</p> Signup and view all the answers

    What is a Brönsted-Lowry acid?

    <p>A substance that donates protons</p> Signup and view all the answers

    What is the value of the ionic product of water, Kw, at 25° C?

    <p>1.0 x 10-14</p> Signup and view all the answers

    Which equation correctly relates [H3O+], [OH-], and Kw?

    <p>Kw = [H3O+][OH-]</p> Signup and view all the answers

    How is pH calculated from [H+]?

    <p>pH = -log10[H+]</p> Signup and view all the answers

    What is the relationship between pH and pOH at 25° C?

    <p>pH + pOH = 14.0</p> Signup and view all the answers

    What is the concentration of H+ in a solution with a pH of 3.00?

    <p>1.0 x 10-3 M</p> Signup and view all the answers

    When H+ concentration is 1.0 x 10-11 M, what is the pOH?

    <p>11.00</p> Signup and view all the answers

    Which of the following behavior of water is correct?

    <p>Water can act both as an acid and a base.</p> Signup and view all the answers

    In the formula -log10(1 x 10-14), what is the resultant pKw value?

    <p>14</p> Signup and view all the answers

    What is indicated by a pH value of 0?

    <p>The solution is acidic.</p> Signup and view all the answers

    What does a larger Ka value indicate about an acid?

    <p>The acid readily donates protons.</p> Signup and view all the answers

    What is the relationship between pKa and acid strength?

    <p>The smaller the pKa, the stronger the acid.</p> Signup and view all the answers

    Which of the following acids is considered a strong acid?

    <p>Hydrochloric acid HCl</p> Signup and view all the answers

    What indicates that a reaction is exergonic?

    <p>There is a net release of free energy.</p> Signup and view all the answers

    In the context of acid dissociation, what does Ka < 1 indicate?

    <p>The acid is weak.</p> Signup and view all the answers

    What does it mean if an acid is 100% ionized in water?

    <p>It is a strong acid.</p> Signup and view all the answers

    Which of the following statements about equilibrium constants is true?

    <p>All of the above.</p> Signup and view all the answers

    Which acid has the highest pKa value in the provided data?

    <p>NH3</p> Signup and view all the answers

    What signifies that a reaction is not spontaneous?

    <p>Keq &lt; 1</p> Signup and view all the answers

    Which of the following pairs correctly represent an acid and its corresponding Ka value?

    <p>Water - $1.8 x 10^{-16}$</p> Signup and view all the answers

    Study Notes

    Coordination of Enzymes in Glucose to ATP Conversion

    • Metabolic pathways include glycolysis, gluconeogenesis, glycogen metabolism, the citric acid cycle, and oxidative phosphorylation (electron transport chain and ATP synthesis).

    Enzyme Regulatory Strategies and Metabolic Pathways

    • This section (slides 9-16) was covered in previous courses; review as needed. Only slide 10's summary will be explained in class.

    Covalent and Noncovalent Interactions in Biological Molecules

    • Crucial for the stability of biological molecules.

    Electrostatic (Ionic) Interactions

    • Occur between charged groups, forming salt bridges.
    • Can be attractive or repulsive.
    • Also occur between charged species and permanent dipoles.
    • Strength varies depending on the species involved, following Coulomb's Law: F = kq₁q₂/Dr².
    • Bond energy is approximately 5.8 kJ/mol for singly charged ions separated by 3Å in water.

    van der Waals Interactions

    • Weak interactions between all atoms, regardless of polarity.
    • Includes attractive (dispersion) and repulsive (steric) components.
    • Attraction dominates at longer distances; most favorable energy is at van der Waals contact distance. Closer proximity results in electron-electron repulsion.
    • Bond energy: 2–4 kJ/mol.

    London Dispersion Forces

    • Result from transient, temporary electronic asymmetries inducing complementary interactions in neighboring molecules.
    • Stronger in polarizable molecules.
    • Significant only at short range.

    Hydrophobic Interactions

    • Nonpolar molecules aggregate in polar solvents (like water).
    • Hydrophobic amino acids tend to cluster together, avoiding water.

    Amino Acid Properties

    • The 20 amino acids in proteins have diverse side chains varying in size, shape, charge, hydrogen-bonding capability, hydrophobic/hydrophilic character, and chemical reactivity. These properties determine protein function.

    Hydrophobic Amino Acids

    • Tend to cluster together and avoid water. Glycine is the least hydrophobic; phenylalanine is the most (among those listed). Glycine is achiral; isoleucine has two chiral centers.

    Proline

    • Contains a secondary amine, restricting its conformation—a key feature used by proteins.

    Polar Amino Acids

    • Have side chains with electronegative atoms forming hydrogen bonds. These polar groups make them hydrophilic. Cysteine is an exception, forming disulfide bonds and partial deprotonation at physiological pH.

    Cysteine and Disulfide Bonds

    • Cysteine can form disulfide bonds.

    Aromatic Amino Acids

    • Phenylalanine is purely hydrophobic; tryptophan and tyrosine are less hydrophobic due to OH and NH groups. Tyrosine shows some polarity. All three absorb UV light at ~280 nm.

    Acid-Base Reactions: Proton Transfer

    • Brønsted-Lowry acid: proton donor.
    • Brønsted-Lowry base: proton acceptor.
    • Water can act as both an acid and a base (autoionization).
    • Conjugate acid-base pairs exist.

    Water Autoionization

    • H₂O (l) + H₂O (l) ⇌ OH⁻ (aq) + H₃O⁺ (aq)
    • Keq (equilibrium constant) = 1.8 x 10⁻¹⁶ at 25°C.
    • Kw (ionic product of water) = Keq x [H₂O] = [OH⁻][H⁺] = 1.0 x 10⁻¹⁴ at 25°C.

    pH and pOH

    • pH = -log₁₀[H⁺]
    • pOH = -log₁₀[OH⁻]
    • pH + pOH = 14.00 at 25°C

    Acid Equilibrium Constants

    • Ka (acid dissociation constant) = [H₃O⁺][A⁻]/[HA]
    • pKa = -log₁₀Ka
    • Larger Ka or smaller pKa indicates a stronger acid.

    Ionization Constants of Acids

    • A table displays ionization constants (Ka and pKa values) for various acids, demonstrating relative acid strength.

    Thermodynamics and Reaction Spontaneity

    • Spontaneity is determined by thermodynamics. Spontaneous reactions are exergonic (ΔG < 0, Keq > 1), non-spontaneous reactions are endergonic (ΔG > 0, Keq < 1), and reactions at equilibrium have ΔG = 0 and Keq = 1.

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