Protein Structure Levels
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Questions and Answers

What is the primary structure of a protein?

  • The three-dimensional structure of a polypeptide
  • The local spatial arrangement of a polypeptide's backbone atoms
  • The association of subunits in the tertiary structure
  • The sequence of amino acids linked by a peptide bond (correct)

    • What is required to break peptide bonds nonenzymatically?

  • Enzymatic reaction
  • Heating and high concentrations of urea
  • Prolonged exposure to a strong acid or base at elevated temperatures (correct)
  • Cooling and low concentrations of urea

    • How many possible unique polypeptide chains of 100 residues are there?

  • 20^100 ≈1.27 ×10^130 (correct)
  • 20^10 ≈1.27 ×10^13
  • 20^50 ≈1.27 ×10^65
  • 20^20 ≈1.27 ×10^26

    • What determines the 3D structure of a protein?

    <p>The sequence of amino acids</p> Signup and view all the answers

    What is the minimum number of residues a protein typically contains?

    <p>40 residues</p> Signup and view all the answers

    What is the function of oxytocin?

    <p>Uterine contraction during labor and promoting milk release during lactation</p> Signup and view all the answers

    What is the number of amino acids in oxytocin and vasopressin?

    <p>9 AAs</p> Signup and view all the answers

    What is the definition of a peptide?

    <p>A polypeptide chain of less than 40 residues</p> Signup and view all the answers

    What is the primary function of vasopressin in the kidney?

    <p>Increase water reabsorption</p> Signup and view all the answers

    What is the role of glutathione in biological systems?

    <p>Antioxidant activity</p> Signup and view all the answers

    What is the characteristic of the peptide bond?

    <p>It is shorter than a single bond and is rigid and planar</p> Signup and view all the answers

    What is the consequence of the peptide bond's partial double-bond character?

    <p>Prevention of free rotation around the bond</p> Signup and view all the answers

    Which bond angles are freely rotatable in a polypeptide chain?

    <p>Cα-N and Cα-C</p> Signup and view all the answers

    What is the significance of the omega angle in a peptide bond?

    <p>It is always 0 or 180° for cis and trans, respectively</p> Signup and view all the answers

    What is the purpose of the Ramachandran plot?

    <p>To indicate the allowed conformations of polypeptides</p> Signup and view all the answers

    What are the sterically forbidden conformations in a polypeptide chain?

    <p>Those with ϕ and ψ values that bring atoms closer than the van der Waals distance</p> Signup and view all the answers

    Study Notes

    Protein Structure Levels

    • Primary structure: the sequence of amino acids linked by a peptide bond
    • Secondary structure: local spatial arrangement of a polypeptide's backbone atoms without regard to the conformations of its side chains
    • Tertiary structure: three-dimensional structure of an entire polypeptide, including its side chains
    • Quaternary structure: association of subunits in the tertiary structure to form multimeric protein

    Primary Structure

    • Sequence of amino acids in a protein is called the primary structure of the protein
    • Peptide bonds are resistant to heating and high concentrations of urea
    • Prolonged exposure to a strong acid or base at elevated temperatures is required to break these bonds nonenzymatically
    • Theoretical possibilities for polypeptides are unlimited (20n possible sequences for a protein of n residues)
    • Amino acid sequence determines the 3D structure of a protein

    Biologically Active Peptides

    • Oxytocin and vasopressin are biologically active peptides (hormones) composed of 9 amino acids
    • Oxytocin: uterine contraction during labor & promoting milk release during lactation
    • Vasopressin: antidiuretic hormone; increases water reabsorption in the kidney & promotes the constriction of blood vessels, thereby increasing blood pressure
    • Glutathione: a tripeptide with antioxidant activity, maintaining sulfhydryl groups of proteins in the reduced state and the iron of heme in the ferrous (Fe2+) state

    Peptide Bond Characteristics

    • Peptide bond has a partial double-bond character, making it rigid and planar, preventing free rotation around the bond
    • Bonds between the α-carbons and the α-amino group (Cɑ-N) or between the α-carbons and α-carboxyl groups (Cɑ-C) can be freely rotated

    Ramachandran Plot

    • The Ramachandran Diagram indicates allowed conformations of polypeptides based on sterically allowed values of φ and ψ
    • Sterically forbidden conformations have φ and ψ values that would bring atoms closer than the corresponding van der Waals distance

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    Description

    This quiz covers the four levels of protein structure, including primary, secondary, tertiary, and quaternary structures. Learn about the sequence of amino acids, spatial arrangements, and associations of subunits.

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