PGY 2320 Medical Biochemistry Quiz
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Questions and Answers

What role does water play in biological systems?

  • It is primarily an energy source.
  • It eliminates the need for other solvents.
  • It acts as a temperature regulator. (correct)
  • It reduces reaction rates in organisms.

    • What type of bond exists between the oxygen and hydrogen atoms in a water molecule?

  • Polar covalent bond (correct)
  • Hydrogen bond
  • Nonpolar covalent bond
  • Ionic bond

    • How many hydrogen bonds can each water molecule form?

  • Five
  • Two
  • Four (correct)
  • Three

    • What happens to the density of water as it cools?

    <p>It decreases.</p> Signup and view all the answers

    What contributes to water's high specific heat?

    <p>Hydrogen bonds between water molecules</p> Signup and view all the answers

    What is the significance of the permanent dipole in a water molecule?

    <p>It creates attractions for other polar molecules.</p> Signup and view all the answers

    What structural property of water results in ice being less dense than liquid water?

    <p>Formation of an open lattice structure.</p> Signup and view all the answers

    What is the process called when water molecules surround ions?

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

    What determines the relative solubility of substances in water?

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

    Which of the following functional groups increases the solubility of a molecule in water?

    <p>Polar functional groups</p> Signup and view all the answers

    Why are nonpolar molecules excluded from interacting with water?

    <p>They cannot form hydrogen bonds</p> Signup and view all the answers

    Which statement is TRUE about hydrogen bonds in water?

    <p>They cause water to have a high melting point.</p> Signup and view all the answers

    What characterizes amphipathic molecules?

    <p>They have both hydrophilic and hydrophobic parts</p> Signup and view all the answers

    What structure is formed by the hydrophilic heads and hydrophobic tails of amphipathic molecules?

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

    Which of the following is NOT a major noncovalent force involved in biomolecule structure?

    <p>Covalent bonds</p> Signup and view all the answers

    What stabilizes the structures of proteins and nucleic acids?

    <p>Hydrogen bonds</p> Signup and view all the answers

    What is the primary role of hydrophobic interactions in biological systems?

    <p>Stabilizing protein shape and membrane structures</p> Signup and view all the answers

    Which of the following accurately describes electrostatic interactions?

    <p>They are significantly weakened by water molecules.</p> Signup and view all the answers

    What characterizes van der Waals forces?

    <p>They depend on the distance between two atoms.</p> Signup and view all the answers

    Which of the following is an example of a nucleophile?

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

    What is produced when pure water ionizes?

    <p>Hydrogen ions and hydroxide ions</p> Signup and view all the answers

    How are hydrogen ions typically represented in solution?

    <p>As hydrated H3O+ ions</p> Signup and view all the answers

    What role does ATP play in condensation reactions?

    <p>It helps to exclude water, making reactions more favorable.</p> Signup and view all the answers

    What is the approximate probability of a hydrogen atom in pure water existing as a hydrogen ion?

    <p>1.8 × 10−9</p> Signup and view all the answers

    What is the value of the ion product of water (Kw) at 25°C?

    <p>$1.0 x 10^{-14} M^2$</p> Signup and view all the answers

    What does a pH of less than 7 indicate about a solution?

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

    How does the concentration of H+ change with a one unit change in pH?

    <p>Increases or decreases by a factor of 10</p> Signup and view all the answers

    What defines a proton donor in acid-base chemistry?

    <p>A substance that loses its proton</p> Signup and view all the answers

    What do acetic acid (CH3COOH) and acetate (CH3COO-) represent?

    <p>Conjugate acid-base pair</p> Signup and view all the answers

    What does the term pKa represent?

    <p>The pH at which an acid is half dissociated</p> Signup and view all the answers

    How does the strength of an acid relate to its pKa value?

    <p>Stronger acids have lower pKa values</p> Signup and view all the answers

    In what way do weak acids differ from strong acids in terms of dissociation in water?

    <p>Weak acids ionize only slightly in water</p> Signup and view all the answers

    What does the dissociation constant (Ka) of a weak acid indicate?

    <p>The strength of an acid in a solution</p> Signup and view all the answers

    How can the pH of a solution be calculated using the Henderson-Hasselbalch equation?

    <p>By determining the ratio of conjugate base to acid and knowing the pKa</p> Signup and view all the answers

    When calculating pH from hydroxide ion concentration, what is the relationship between pH and pOH?

    <p>pH + pOH = 14</p> Signup and view all the answers

    What is the effect of buffers on pH when small amounts of acid or base are added?

    <p>Buffers tend to resist changes in pH</p> Signup and view all the answers

    If the pKa of acetic acid is 4.8, which of the following pH values would indicate a stronger acidic solution?

    <p>4.5</p> Signup and view all the answers

    What defines the molar proportion of A- to HA in the Henderson-Hasselbalch equation?

    <p>It reflects the buffer capacity of the solution</p> Signup and view all the answers

    Which acid would be classified as a weaker acid based on its dissociation constant?

    <p>Monohydrogen phosphate</p> Signup and view all the answers

    Given a solution of acetic acid and acetate ion, what is required to calculate its pH?

    <p>The pKa of acetic acid and the molar proportion of A- to HA</p> Signup and view all the answers

    What is the primary cause of respiratory acidosis?

    <p>Alveolar hypoventilation</p> Signup and view all the answers

    Which condition is most commonly associated with hyperventilation?

    <p>Respiratory alkalosis</p> Signup and view all the answers

    What is a common cause of metabolic acidosis?

    <p>Ingestion of strong organic acids</p> Signup and view all the answers

    What maintains the physiological pH in cells and tissues?

    <p>Acid-base buffers</p> Signup and view all the answers

    What can cause metabolic alkalosis?

    <p>Prolonged vomiting</p> Signup and view all the answers

    What condition arises from excessive intake of alkali substances?

    <p>Metabolic alkalosis</p> Signup and view all the answers

    What is one consequence of increased environmental pH in the body?

    <p>Decreased enzyme activity</p> Signup and view all the answers

    Which buffer system is commonly found in cellular fluids?

    <p>Phosphate buffer</p> Signup and view all the answers

    Study Notes

    Course Information

    • Course: PGY 2320 (Medical Biochemistry & Genetics)
    • Year: 2023/2024
    • Instructor: Dr. Lubinda Mukololo
    • Email: [email protected]
    • Department: Physiological Sciences
    • School: Medicine
    • University: The University of Zambia

    Biophysical Chemistry Objectives

    • Properties of water as a solvent for biochemical reactions
    • Hydrogen bonding
    • Weak acids and bases
    • pH and pKa determination
    • Buffers and their role in biological systems
    • Physiologically important buffer systems

    Water's Importance in Living Systems

    • Solvent/medium for reactions
    • Principal reactant in biological processes (e.g., photosynthesis) and final product in aerobic energy metabolism
    • Determines the shape of biomolecules due to aqueous environments
    • Stabilizes temperature and pH of living organisms

    Properties of Water (1. Polarity)

    • Covalent bonds between oxygen and hydrogen atoms (bond angle of 104.5°)
    • Oxygen is more electronegative than hydrogen, resulting in a polar covalent bond
    • Creates a permanent dipole in the water molecule
    • Determines relative solubility of molecules ("like dissolves like")

    Properties of Water (2. Hydrogen Bonds)

    • Polar covalent bonds lead to attraction between water molecules
    • Hydrogen bonds form between slightly positive hydrogen atom of one water molecule and slightly negative oxygen atom of another water molecule
    • Each water molecule can form hydrogen bonds with four other water molecules
    • Hydrogen bond length is approximately twice that of a covalent bond
    • Weaker than covalent bonds (about 25x weaker)

    Properties of Water (3. Hydrogen Bonds and Melting/Freezing/Density)

    • Hydrogen bonds give water a high melting point
    • Water expands as it freezes, decreasing its density
    • Ice results from an open lattice structure of water molecules
    • Ice is less dense but more ordered than liquid water

    Properties of Water (4. High Specific Heat and Heat of Vaporization)

    • Hydrogen bonds contribute to water's high specific heat
    • Hydrogen bonds must be broken to increase kinetic energy and temperature
    • Water has a high heat of vaporization due to the need to break hydrogen bonds to change water from liquid to gaseous state

    Water as a Universal Solvent

    • Water interacts with and dissolves polar compounds and ionized compounds (electrolytes) due to hydrophilicity
    • Water molecules align around electrolytes creating solvation spheres
    • Solubility of organic molecules in water depends on polarity and ability to form hydrogen bonds with water

    Functional groups that confer solubility in water

    • carboxylates
    • protonated amines
    • amino
    • hydroxyl groups
    • carbonyl groups
    • The number of polar groups in a molecule increases its solubility in water

    Hydrophobic Interactions

    • Nonpolar molecules are not soluble in water
    • Water molecules prefer to interact with each other rather than nonpolar molecules, excluding them
    • Nonpolar molecules associate with each other due to the hydrophobic effect
    • Hydrophobic interactions result from the organization of water molecules around non-polar molecules

    Amphipathic Molecules (e.g., detergents or surfactants)

    • Have both hydrophilic and hydrophobic portions
    • Typically have a hydrophobic chain of 12 carbon atoms plus an ionic or polar end
    • Soaps are alkali metal salts of long-chain fatty acids
    • Examples of detergents: sodium palmitate, sodium dodecyl sulfate

    Micelles

    • Spheres formed by amphipathic molecules with hydrophilic heads facing outward and hydrophobic tails facing inward
    • Used to trap grease and oils

    Noncovalent Interactions in Biomolecules

    • Hydrogen bonds: important in stabilizing structures (proteins, nucleic acids) when they occur between molecules
    • Hydrophobic interactions: very weak intermolecular forces, important for protein shape and membrane structure
    • Charge-charge interactions (ionic bonds): strongest non-covalent force over longer distances, weaken due to water molecules
    • Van der Waals forces: weak attractions or repulsions determined by distance

    Nucleophilic Nature of Water

    • Electron-rich (nucleophiles) attract electron-deficient (electrophiles)
    • Negatively charged or with unshared electrons, nucleophiles attack electrophiles during substitution or addition reactions
    • Examples of nucleophiles: oxygen, nitrogen, sulfur, carbon, and water (weak)

    Condensation and Hydrolysis Reactions

    • Important in condensation reactions, where hydrolysis reactions are favored.
    • Condensation reactions usually use ATP and exclude water to make reactions more favorable
    • Intracellular reactions in the presence of hydrolases

    Ionization of Water

    • Pure water ionizes slightly, forming hydrogen ions (protons) and hydroxide ions
    • Can act as an acid (proton donor) or base (proton acceptor)
    • Hydrogen ions formed immediately become hydrated to hydronium ions
    • Actual probability of a hydrogen atom being an hydrogen ion is approximately 1.8 * 10-9

    Equilibrium Constant for Water

    • Keq = [H+][OH-]/[H₂O] = 1.8 x 10-16M at 25°C
    • In pure water at 25°C, concentration of water is 55.5 M

    pH (Definition and Calculations)

    • pH measures the concentration of H+ in a solution
    • pH = -log [H+]
    • pH < 7 is acidic, pH > 7 is basic (or alkaline)
    • One change in pH = 10 fold change in [H+]
    • pKa = -log Ka
    • pKw =pH + pOH = 14

    Weak Acids and Bases

    • Ionize slightly in water
    • Have characteristic dissociation constants
    • Common in biological systems; important for metabolism and regulation
    • Acids are proton donors, bases are proton acceptors

    Conjugate Acid-Base Pairs

    • A proton donor and its corresponding proton acceptor make up a conjugate acid-base pair

    pKa (definition)

    • pKa of an acid is the pH at which the acid is half dissociated; [A-] = [HA]

    Henderson-Hasselbalch Equation

    • Describes the dissociation of a weak acid in the presence of its conjugate base
    • Important in calculating pH with known concentrations and pKa values

    Buffers

    • Resist changes in pH
    • Consist of a weak acid and its conjugate base or weak base and its conjugate acid

    Importance of Buffers in the Body

    • Enzymes are sensitive to pH
    • Intracellular and extracellular fluids maintain a near constant pH
    • The body is protected from pH changes resulting from continuous production of acids and bases through metabolic processes
    • Organisms first line of defense against pH changes is provided by buffer systems

    Biological Buffers

    • Examples: HCO3-, Phosphate, proteins
    • Proteins contain amino acids and functional groups
    • Phosphate groups of nucleotides function as weak acids

    Phosphate Buffer System

    • Major intracellular buffering systems
    • Acts in cytoplasm of all cells
    • Consists of H₂PO₄⁻ as proton donor and HPO₄²⁻ as proton acceptor
    • Maximally effective between pH 5.9 and 7.9 ( pKa ~ 6.86)

    Bicarbonate Buffer System

    • Main blood plasma buffer
    • Consists of H₂CO₃ as proton donor and HCO₃⁻ as proton acceptor
    • Complex because carbonic acid is formed by reaction of CO₂ and water
    • pH depends on H₂CO₃ (dissolved CO₂) and HCO₃⁻

    Human Blood Plasma pH

    • Normal pH is ~7.4
    • Changes in pH can cause cell damage or death in certain health conditions

    Clinical Disorders in Acid-Base Balance

    • Respiratory acidosis: alveolar hypoventilation, airway obstruction, neuromuscular disorders
    • Respiratory alkalosis: hyperventilation due to anxiety, salicylate poisoning, fever, high altitude
    • Metabolic acidosis: excess lactic acid, acetoacetic acid, β-hydroxybutyric acid, ingestion of salicylates, ethylene glycol, or methyl alcohol
    • Metabolic alkalosis: intake of alkaline materials, abnormal loss of acid (prolonged vomiting)

    Summary

    • Water is a polar molecule with unique properties
    • Most metabolic processes occur in an aqueous environment
    • Numerous weak, non-covalent interactions influence macromolecule folding (e.g., proteins, nucleic acids)

    Summary (cont.)

    • A weak acid (or base) and its salt resist changes in pH due to the addition of H⁺ or OH⁻; mixture functions as a buffer
    • Phosphate and bicarbonate buffer systems maintain optimal (physiological) pH in cells and tissues (~pH 7) which is optimal for enzymatic activity

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    Description

    Test your knowledge on the properties of water and its critical role in biochemical reactions. This quiz covers topics such as hydrogen bonding, pH, buffers, and the importance of water in living systems. Perfect for students in the Medical Biochemistry & Genetics course.

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