Protein Structure and Forces
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Questions and Answers

What is the average number of amino acids found in one alpha helix within a globular protein?

  • 2-15
  • 6
  • 53
  • 11 (correct)

    • Which of the following amino acids is most likely to be found on the surface of a globular protein, interacting with water molecules?

  • Methionine
  • Leucine
  • Glutamic Acid (correct)
  • Valine

    • Which of the following statements is TRUE about the beta-pleated sheet structure?

  • It is held together by hydrogen bonds between neighboring peptide bonds. (correct)
  • It is found only in fibrous proteins.
  • It has a slight left-handed twist.
  • It is always made up of parallel strands.

    • What is a domain in a protein?

    <p>A region of a protein with a specific function. (D)</p> Signup and view all the answers

    Which of the following proteins has a high percentage of alpha helix structure?

    <p>Myoglobin (D)</p> Signup and view all the answers

    What is the difference between a dimer and a tetramer?

    <p>A dimer has two subunits, while a tetramer has four subunits. (B)</p> Signup and view all the answers

    Which of the following is an example of a protein with a quaternary structure?

    <p>Hemoglobin (A)</p> Signup and view all the answers

    Which type of amino acid is MOST LIKELY to be found in the interior of a globular protein?

    <p>Valine (C)</p> Signup and view all the answers

    Which of the following statements about keratin is incorrect?

    <p>Keratin is rich in hydrophobic amino acids, which promote the formation of beta-pleated sheets. (B)</p> Signup and view all the answers

    What is the main structural component of hair?

    <p>Keratin (B)</p> Signup and view all the answers

    Which of the following statements about collagen is correct?

    <p>Collagen forms a triple helix of three polypeptide chains. (A)</p> Signup and view all the answers

    What is the significance of disulfide bridges in keratin?

    <p>They determine the overall shape of the hair. (B)</p> Signup and view all the answers

    What is the role of molecular chaperones in protein folding?

    <p>They assist in the proper folding of polypeptides. (B)</p> Signup and view all the answers

    Why is the structure of protofilaments in keratin stable?

    <p>The disulfide bridges and hydrogen bonds between keratin chains contribute to stability. (A)</p> Signup and view all the answers

    The central dogma of protein folding states that:

    <p>The primary structure determines the tertiary structure. (C)</p> Signup and view all the answers

    Which of the following statements is true about the protein folding process?

    <p>Protein folding is a spontaneous and usually begins with the formation of secondary structures. (C)</p> Signup and view all the answers

    Which of the following statements is TRUE about the structure of myoglobin?

    <p>Myoglobin has 5 non-helical segments, including NA1-NA2, CD, EF, GH, and HC1-HC5. (A), Myoglobin has 8 helical segments, denoted by A, B, C, D, E, F, G &amp; H. (D)</p> Signup and view all the answers

    Which of the following amino acids is NOT found in the interior of myoglobin?

    <p>Glutamic acid (A)</p> Signup and view all the answers

    Which of the following statements correctly describes the heme group in hemoglobin?

    <p>Each heme group in hemoglobin contains an iron atom responsible for oxygen binding. (A)</p> Signup and view all the answers

    How many subunits does hemoglobin have, and how many oxygen molecules can it bind?

    <p>4 subunits, 4 oxygen molecules (A)</p> Signup and view all the answers

    What is the difference between the relaxed (R) and tense (T) structures of hemoglobin?

    <p>The R structure has a higher oxygen affinity, while the T structure has a lower oxygen affinity. (A)</p> Signup and view all the answers

    What is the primary function of hemoglobin in the blood?

    <p>Hemoglobin carries oxygen from the lungs to the tissues. (D)</p> Signup and view all the answers

    What causes the change between the T and R structures of hemoglobin?

    <p>A rotation of 15 degrees between the two alpha-beta dimers. (A)</p> Signup and view all the answers

    Which of the following statements is TRUE about the α-subunits of hemoglobin?

    <p>The α-subunits have 7 helical segments, missing the D segment. (A)</p> Signup and view all the answers

    Flashcards

    Alpha Helix

    A helical structure in proteins formed by hydrogen bonds between peptide bonds.

    Beta Structure

    A secondary structure in proteins formed by hydrogen bonds, resulting in pleated sheets.

    Parallel Beta Sheets

    Beta structure where chains run in the same direction, stabilizing the sheet.

    Anti-parallel Beta Sheets

    Beta structure where chains run in opposite directions, more common in proteins.

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    Globular Proteins

    Proteins that have a compact, rounded shape and contain various arrangements of secondary structures.

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    Protein Domains

    Distinct structural or functional units within a protein, often large proteins contain them.

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    Quaternary Structure

    The fourth level of protein structure involving multiple polypeptide chains forming a larger protein.

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    Oligomeric Proteins

    Proteins made of two or more polypeptide chains, referred to as subunits or monomers.

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    Hemoglobin Structure

    A tetramer with 2 alpha and 2 beta subunits.

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    Central Dogma of Protein Folding

    The primary structure determines the tertiary structure.

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    Protein Folding Process

    Spontaneous process starting with local secondary structures.

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    Molecular Chaperones

    Proteins that assist in protein folding.

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    Keratin

    A fibrous protein that is a primary component of hair.

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    Collagen

    A structural protein forming a triple helix.

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    Myoglobin Discovery

    Elucidated structure by John Kendrew & Max Perutz using x-ray crystallography.

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    Fibrils Formation

    Coiled-coils form protofilaments that create microfibrils.

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    Myoglobin

    A small protein that carries oxygen in muscle tissue, composed of 153 amino acids and has a heme prosthetic group.

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    Heme Group

    A tetrapyrrole structure in myoglobin and hemoglobin that contains an iron atom, responsible for oxygen binding.

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    Structure of Myoglobin

    Consists of 75% alpha helices and 5 non-helical segments, compact without empty spaces.

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    Hemoglobin

    A protein in red blood cells that carries oxygen and carbon dioxide, consisting of 4 polypeptide chains (2α, 2β).

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    Oxygen Binding in Hemoglobin

    Each hemoglobin subunit can carry one oxygen molecule, allowing high oxygen carrying capacity.

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    Tense vs. Relaxed Structure

    Hemoglobin can exist in two forms: T (tense, low oxygen affinity) and R (relaxed, high oxygen affinity).

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    Rotation between Subunits

    The transition from T to R structure in hemoglobin involves a 15-degree rotation of alpha-beta dimers affecting oxygen affinity.

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    Iron in Heme

    In the heme group, Fe2+ can bind 6 atoms, crucial for oxygen transport like myoglobin.

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    Study Notes

    Protein Structure

    • Proteins are large, complex molecules vital for numerous cellular functions.
    • Their function hinges on their specific three-dimensional shape.
    • The sequence of amino acids in a polypeptide chain determines the protein's overall structure.

    Forces Influencing Protein Structure

    • Hydrogen bonds form between peptide groups in the protein backbone.
    • Hydrogen bonds form between side chains.
    • Hydrophobic interactions occur between non-polar side chains.
    • Hydrophilic interactions occur between polar side chains.
    • Ionic bonds form between oppositely charged side chains.
    • Disulfide bonds link cysteine side chains.

    Secondary Structures

    • Alpha-helix: A predominantly right-handed helical structure stabilized by hydrogen bonds between the N-H group of one peptide bond and the C=O group of another, typically four amino acids apart.
    • Average amino acids per helix is around 11, though this can vary up to 53.
    • Beta-sheet: A pleated sheet structure in which multiple β-strands are arranged parallel or anti-parallel. Hydrogen bonds between the polypeptide backbone of adjacent strands stabilize the structure.
    • Parallel and anti-parallel beta strands are two possible variations.
    • Average amino acids per sheet is between 2-15, with an average of 6.

    Tertiary Structures

    • The overall 3D structure of a polypeptide chain.
    • The arrangement of secondary structures.
    • Proteins often contain hydrophobic amino acids nestled inside the folded structure and hydrophilic amino acids on the outside, to facilitate water solubility.
    • Myoglobin and hemoglobin are examples of proteins with a predominant alpha-helical structure and a compact shape.
    • Concanavalin A is an example of a protein with predominantly beta-sheet structure.
    • Supersecondary structures/motifs are formed by combinations of secondary structures.

    Quaternary Structures

    • The structure resulting from the interaction of multiple polypeptide chains.
    • Proteins with more than one polypeptide chain are called oligomeric.
    • Individual chains within an oligomeric structure are called subunits or monomers.
    • Examples: Haemoglobin, Myoglobin, Muscle creatine kinase.

    Central Dogma of Protein Folding

    • Primary structure dictates the tertiary structure.
    • Protein folding is a spontaneous process.
    • Local secondary structures form a nucleus, around which the rest of the protein folds.
    • Molecular chaperones aid protein folding, especially under stress conditions.

    Selected Protein Structures

    • Fibrous Proteins:
      • Primarily structural proteins.
      • Examples: Keratin, Collagen, Silk.
    • Globular Proteins:
      • Perform metabolic functions including transport, catalysis (e.g., enzymes), hormone function.
      • Examples: Myoglobin, Hemoglobin.

    Denaturing Proteins

    • Proteins denature when bonds maintaining their shape are broken.
    • Temperature, pH, or salt concentration changes can cause denaturation.
    • Denatured proteins lose function and often become insoluble.
      • Fibrous Proteins: lose structural strength when denatured
      • Globular Proteins: become insoluble and inactive.

    Myoglobin

    • Myoglobin's structure was determined through x-ray crystallography.
    • Contains 153 amino acids with 75% in alpha-helix and 8 helix segments (A to H).
    • Its compact shape facilitates oxygen binding.
    • It has a prosthetic group, haem, essential for oxygen transport

    Hemoglobin

    • Haemoglobin is a critical oxygen-transport protein.
    • It has four protein chains (2 alpha and 2 beta). Each subunit can carry one oxygen molecule, making its capacity to carry oxygen high.
    • Each subunit has 7-8 helical segments like myoglobin.
    • Its quaternary structure enables cooperative oxygen binding and release.
    • Haemoglobin has different conformations (R and T states) related to oxygen binding affinity.
    • Changes in haemoglobin structure cause conditions like sickle-cell anemia.

    Differences between Collagen and Haemoglobin

    Feature Collagen Haemoglobin
    Polypeptide Chains Not identical; 3 Identical; 4
    Prosthetic Group No Yes (Haeme)
    Structure Fibrous Globular
    Tertiary Structure No Yes
    Repeating Amino Acids Glycine Less glycine, varies

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    Basic Biochemistry Amino Acid and Protein PDF

    Description

    This quiz covers the essential aspects of protein structure, including the various forces that influence their formation. Understand the significance of amino acid sequences and explore secondary structures such as alpha-helices and beta-sheets. Test your knowledge of protein biology and the interactions that stabilize protein shapes.

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