Amino Acids & Protein Structures
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Questions and Answers

What is the typical range of amino acids found in an alpha helix within a globular protein?

  • 2-15
  • 6-12
  • 25-75
  • 11-53 (correct)

    • Which type of amino acid is generally found on the surface of globular proteins?

  • Hydrophobic
  • Non-polar
  • Neutral
  • Polar and charged (correct)

    • What is the name given to the structure formed by the interaction of two or more polypeptide chains?

  • Secondary structure
  • Quaternary structure (correct)
  • Super secondary structure
  • Tertiary structure

    • Which of these is NOT a characteristic of the alpha helix?

    <p>Found frequently in the central core of globular proteins (B)</p> Signup and view all the answers

    What is the difference between parallel and anti-parallel beta sheets?

    <p>The direction of the polypeptide chains (B)</p> Signup and view all the answers

    Which of these proteins is an example of a protein with only beta structures?

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

    Which of the following is an accurate statement about super secondary structures?

    <p>They are formed by the interaction of alpha helices and beta sheets (A)</p> Signup and view all the answers

    A protein with two identical polypeptide chains is called a:

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

    Which of these is true about the folding of proteins?

    <p>The tertiary structure of a protein is determined by its primary structure. (A)</p> Signup and view all the answers

    What is the primary function of keratin?

    <p>To provide strength and flexibility to tissues like hair, skin and nails. (D)</p> Signup and view all the answers

    What type of secondary structure is found in keratin?

    <p>Alpha-helix (A)</p> Signup and view all the answers

    What type of bonds are most important in stabilizing the structure of keratin?

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

    What is the main structural unit of collagen?

    <p>A triple helix of three collagen polypeptides (A)</p> Signup and view all the answers

    Which of these is NOT a characteristic of collagen?

    <p>Abundant in hydrophobic amino acids (A)</p> Signup and view all the answers

    What is the main function of myoglobin?

    <p>To store oxygen in muscle tissue (C)</p> Signup and view all the answers

    Which of these is true about hemoglobin?

    <p>Hemoglobin contains four polypeptide chains, two alpha and two beta. (C)</p> Signup and view all the answers

    What is the key difference between the α and β subunits of hemoglobin?

    <p>The α subunits lack the D helix, while the β subunits have 8 helical segments. (C)</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 α-β dimers causes the heme molecule to change positions. (D)</p> Signup and view all the answers

    What amino acids are commonly found in the interior of myoglobin, contributing to its compact structure?

    <p>Leu, Val, Met, Phe (A)</p> Signup and view all the answers

    Which of the following statements accurately describes the role of the heme group in hemoglobin?

    <p>The heme group, containing an iron atom, is responsible for the binding of oxygen. (D)</p> Signup and view all the answers

    How does the relaxed (R) structure of hemoglobin differ from the tense (T) structure?

    <p>The relaxed structure has a higher oxygen affinity compared to the tense structure. (B)</p> Signup and view all the answers

    Why is myoglobin ideal for studying protein structure?

    <p>Myoglobin is relatively small, crystallizes easily, and has a prosthetic group (heme), making it amenable to structural studies. (D)</p> Signup and view all the answers

    What is the key role of hemoglobin in the body?

    <p>To transport oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs. (B)</p> Signup and view all the answers

    What is the significance of the iron atom in the heme group?

    <p>The iron atom binds to oxygen, facilitating its transport by hemoglobin. (D)</p> Signup and view all the answers

    Flashcards

    Alpha Helix

    A right-handed spiral structure formed by hydrogen bonding between neighboring peptide bonds.

    Beta Structure

    A protein structure formed by hydrogen bonds between parallel or anti-parallel peptide chains, creating a pleated sheet.

    Parallel vs Anti-parallel

    Refers to the orientation of chains in a beta structure: chains in the same direction are parallel; in different directions are anti-parallel.

    Globular Protein Composition

    Globular proteins contain approximately 27% alpha helices and 23% beta structures, with variations depending on the specific protein.

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    Hydrophobic amino acids

    Amino acids that are generally found in the interior of proteins, away from water, to avoid interaction with it.

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    Quaternary Structure

    The 3D arrangement of multiple polypeptide chains interacting to form a larger protein molecule.

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    Oligomeric Proteins

    Proteins composed of two or more polypeptide chains, known as subunits or monomers.

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    Domains in Proteins

    Distinct functional regions within a protein, especially larger globular proteins, which can perform specific roles.

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    Haemoglobin structure

    Haemoglobin is a tetramer composed of 2 alpha and 2 beta subunits.

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    Central dogma of protein folding

    The primary structure of a protein determines its tertiary structure.

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    Molecular chaperones

    Proteins assisting in the correct folding of other proteins.

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    Fibrous proteins

    Structural proteins like keratin and collagen; have elongated shapes.

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    Keratin

    A fibrous protein that forms hair, nails, and skin; made of twisted alpha-helices.

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    Collagen

    Most abundant protein in vertebrates, forming a triple helix structure.

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    Myoglobin

    A globular protein that stores oxygen in muscle cells, structure elucidated by Kendrew & Perutz.

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    Protofilaments

    Structures formed by twisting coiled-coils of keratin, contributing to fiber formation.

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    Heme Group

    A prosthetic group in myoglobin and hemoglobin that contains iron, allowing binding to oxygen.

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    Oxygen Binding in Hemoglobin

    Each hemoglobin subunit can bind one molecule of oxygen, enabling transport of four oxygen molecules total.

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    Tense vs Relaxed Structure

    Hemoglobin exists in two states: T (tense) has lower affinity for oxygen, and R (relaxed) has higher affinity.

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    Helix Segments in Proteins

    Myoglobin features 75% of its structure as alpha helices, while hemoglobin has 8 in beta chains and 7 in alpha chains.

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    Iron Ion in Heme

    The iron in heme binds to oxygen, pivotal for oxygen transportation in myoglobin and hemoglobin.

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    Polypeptide Chains

    Fibrous sequences of amino acids that form the structure of proteins like myoglobin and hemoglobin.

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    Study Notes

    Amino Acid & Protein 2

    • Proteins are composed of amino acids linked by peptide bonds.
    • Forces influencing protein structure:
      • Hydrogen bonds between peptide groups.
      • Hydrogen bonds between side chains and peptide groups.
      • Hydrogen bonds between two side chains.
      • Hydrophobic interactions.
      • Ionic bonds.
      • Disulfide bonds.

    Secondary Structures

    • Alpha-helix:
      • Hydrogen bonds between C=O and N-H groups of neighboring peptide bonds.
      • Right-handed helix.
      • Approximately 11 amino acids per helix turn (range up to 53).
    • Beta-sheet:
      • Hydrogen bonds between neighboring peptide bonds in the same or different chains.
      • Parallel or anti-parallel chains.
      • Forms a pleated sheet structure.
      • 2-15 amino acids per sheet (average 6).
      • Anti-parallel more common.
      • Slight right-handed twist.
      • Often found in the central core of globular proteins.

    Tertiary Structures

    • 3D structure of the polypeptide.
    • Arrangement of secondary structures.
    • Super-secondary structures (motifs).
    • Hydrophobic amino acids usually found in the protein interior (e.g., valine, leucine, methionine).
    • Polar and charged amino acids often found on the surface (e.g., glutamic acid, aspartic acid, histidine, lysine).
    • Polar (uncharged) amino acids can be found both inside or outside globular proteins (e.g., serine, asparagine, tyrosine).
    • Large globular proteins (>200 amino acids) often contain domains.
    • Examples: myoglobin, hemoglobin, Concanavalin A.

    Quaternary Structures

    • Interaction of multiple polypeptide chains to form a larger protein molecule.
    • Proteins with multiple chains are called oligomeric.
    • Individual chains are called subunits or monomers.
    • Structures: dimer, trimer, tetramer, etc.
    • Subunits can be identical (homogeneous) or different (heterogeneous).
    • Examples: muscle creatine kinase (dimer), hemoglobin (tetramer).

    Central Dogma of Protein Folding

    • Primary structure determines the tertiary structure.
    • Protein folding is spontaneous.
    • Folding likely starts with local secondary structures (e.g., alpha-helix, beta structures).
    • Molecular chaperones (heat-shocked proteins) assist folding.

    Fibrous Proteins

    • Proteins with a long, rope-like structure
    • Examples:
      • Keratin: Structural component of hair, nails, claws and hooves.
        • Coiled-coils.
        • Protofilaments.
        • Microfibrils.
        • Macrofibrils.
        • α-helix
      • Collagen: Most abundant protein in vertebrates.
        • Component of connective tissue (e.g., ligaments, tendons, cartilage).
        • Triple helix structure.
      • Silk: Forms spider webs and silkworms' cocoons.

    Globular Proteins

    • Proteins with a roughly spherical shape.
      • Hydrophobic amino acids inside.
      • Hydrophilic amino acids outside.
      • Examples:
        • Myoglobin: Oxygen-carrying protein in muscle tissue.
        • Hemoglobin: Oxygen-carrying protein in red blood cells.

    Denaturing Proteins

    • Breaking protein bonds.
      • Breaks the protein shape.
      • Prevents proper function.
    • Causes: Changes in temperature; pH or salt concentration.
    • Fibrous proteins lose structural strength.
    • Globular proteins become insoluble and inactive.

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    Basic Biochemistry Amino Acid and Protein PDF

    Description

    This quiz covers the fundamentals of amino acids and the various levels of protein structure, including secondary and tertiary formations. You'll explore concepts such as hydrogen bonds, alpha-helices, and beta-sheets, as well as the forces that influence protein configuration. Test your understanding of these essential biological macromolecules.

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