Structure-Function Relationship in Proteins
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Questions and Answers

What is the primary role of hemoglobin in the blood?

  • Storing nutrients for energy
  • Transporting gases, particularly oxygen (correct)
  • Transporting carbon dioxide from the lungs
  • Transporting hormones throughout the body

    • Which of the following statements about hemoglobin's structure is true?

  • It consists of four identical polypeptide chains
  • It has a quaternary structure with four polypeptide chains (correct)
  • It has a linear structure made of amino acids
  • It is a monomeric protein with no subunits

    • What happens to hemoglobin when it binds with oxygen?

  • It undergoes a transition from T state to R state (correct)
  • It destabilizes its iron centers
  • It remains in the same T state
  • It loses its allosteric properties

    • How do protons and CO2 affect hemoglobin's affinity for oxygen?

    <p>They decrease hemoglobin's affinity for oxygen (B)</p> Signup and view all the answers

    What is meant by hemoglobin being an allosteric protein?

    <p>Binding at one site affects binding at other sites (D)</p> Signup and view all the answers

    What is the main physiological role of 2,3-bisphosphoglycerate (BPG) in hemoglobin?

    <p>Decrease affinity of hemoglobin for oxygen. (C)</p> Signup and view all the answers

    Which amino acid residues are most commonly found in collagen structure?

    <p>Glycine, Proline, Hydroxyproline. (C)</p> Signup and view all the answers

    What type of structural feature is characteristic of collagen?

    <p>Left-handed helix from three amino acid residues. (A)</p> Signup and view all the answers

    What impact do cross-links have on collagen fibers?

    <p>Increase tensile strength and flexibility. (D)</p> Signup and view all the answers

    Which type of collagen is primarily responsible for providing resistance to tension?

    <p>Type I collagen. (B)</p> Signup and view all the answers

    What is a feature of fibrous proteins that contributes to their structural function?

    <p>High concentration of hydrophobic amino acids. (A)</p> Signup and view all the answers

    Which statement best describes the formation of tropocollagen?

    <p>Consists of three collagen helices twisted together. (C)</p> Signup and view all the answers

    What role does 2,3-bisphosphoglycerate (BPG) play at high altitudes?

    <p>It facilitates the release of oxygen from hemoglobin. (C)</p> Signup and view all the answers

    What is a common name for osteogenesis imperfecta?

    <p>Brittle bone disease (B)</p> Signup and view all the answers

    What substance is primarily deficient in scurvy, leading to collagen issues?

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

    What type of collagen does osteogenesis imperfecta primarily affect?

    <p>Type I collagen (D)</p> Signup and view all the answers

    Which statement correctly describes myosin?

    <p>It is composed of two heavy chains and two light chains. (D)</p> Signup and view all the answers

    What characterizes the thick filaments in myosin?

    <p>They are composed of hundreds of myosin molecules aggregated. (C)</p> Signup and view all the answers

    What is the structure of G-actin?

    <p>It is a monomeric protein. (A)</p> Signup and view all the answers

    Which of the following best describes the structure of F-actin?

    <p>It is made from polymerized G-actin monomers. (C)</p> Signup and view all the answers

    What physical property is associated with the carboxyl terminus of myosin?

    <p>It features an extended α helix. (C)</p> Signup and view all the answers

    What is a key characteristic that distinguishes globular proteins from fibrous proteins?

    <p>Globular proteins have a compact, rounded structure. (D)</p> Signup and view all the answers

    What is the main function of myoglobin in muscle tissue?

    <p>Storing oxygen for intense respiration. (A)</p> Signup and view all the answers

    Which structural feature is unique to hemoglobin compared to myoglobin?

    <p>It has a quaternary structure. (C)</p> Signup and view all the answers

    Which amino acid residue plays a crucial role in coordinating the iron atom within the heme group of myoglobin?

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

    How does the heme group protect iron from oxidation in globular proteins?

    <p>By being positioned in a hydrophobic pocket. (C)</p> Signup and view all the answers

    What is the primary function of hemoglobin in the erythrocytes?

    <p>Transporting oxygen from lungs to tissues and CO2 from tissues to lungs. (A)</p> Signup and view all the answers

    What type of structural arrangement do myoglobin and hemoglobin both share regarding their heme groups?

    <p>They have heme groups located within hydrophobic pockets. (D)</p> Signup and view all the answers

    What is the role of prosthetic groups in conjugated proteins like hemoglobin?

    <p>They enhance the protein's ability to bind to substrates or ligands. (B)</p> Signup and view all the answers

    Flashcards

    Distal His

    A histidine close to the heme but not bound, favoring oxygen entry over CO.

    Oligomeric protein

    A protein with multiple polypeptide chains, like hemoglobin with quaternary structure.

    T state

    The tense state of hemoglobin, lacking oxygen, where binding sites are less available.

    R state

    The relaxed state of hemoglobin when oxygen is bound, facilitating further binding.

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    Allosteric protein

    A protein where ligand binding at one site affects binding at another site, like hemoglobin.

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    Elastic Cartilage

    Cartilage with very thin fibers, supporting structures under intermittent pressure.

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    Types of Collagen Disorders

    Medical conditions related to genetic or metabolic issues affecting collagen structure.

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    Osteogenesis Imperfecta

    A genetic disorder characterized by fragile bones, also known as brittle bone disease.

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    Scurvy

    Disease caused by Vitamin C deficiency, leading to unstable collagen helix.

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    Myosin Structure

    Protein with six subunits, crucial for muscle contraction, includes heavy and light chains.

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    Thick Filaments

    Aggregated myosin molecules that form the core of muscle contractile units.

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    G-actin vs F-actin

    G-actin is a monomer; F-actin is a polymer formed by G-actin monomers.

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    Function of Actin

    Actin plays a role in muscle contraction and structure of the cytoskeleton.

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    Globular proteins

    Soluble proteins with a compact, rounded shape, fulfilling various functions.

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    Myoglobin

    A globular protein that stores oxygen in muscles, featuring a tertiary structure.

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    Hemoglobin

    A globular protein in erythrocytes that transports oxygen from lungs to tissues and CO2 back.

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    Prosthetic group

    A non-polypeptide unit that attaches to a protein to assist its function, e.g., heme in hemoglobin.

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    Heme group

    A complex organic structure containing an iron atom, crucial for oxygen binding in myoglobin and hemoglobin.

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    Apoprotein

    The protein portion without its prosthetic group, e.g., without heme in hemoglobin.

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    Quaternary structure

    The structure formed when multiple polypeptide chains join together, as seen in hemoglobin.

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    Tertiary structure

    The three-dimensional structure of a single polypeptide chain, important in myoglobin.

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    CO2 and Hemoglobin

    CO2 binds to hemoglobin, affecting oxygen transport.

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    2,3-bisphosphoglycerate (BPG)

    BPG decreases hemoglobin's affinity for oxygen at high altitudes.

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    Fibrous Proteins

    Insoluble proteins with high hydrophobic amino acids, adapted for strength.

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    Collagen

    Most abundant fibrous protein in mammals, provides strength to connective tissues.

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    Collagen Helix Structure

    Left-handed helix made of three amino acid residues per turn; Gly–X–Y sequence.

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    Tropocollagen

    Basic unit of collagen; three helices twisted for strength and stability.

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    Cross-linking in Collagen

    Covalent bonds that affect rigidity or flexibility of collagen fibers.

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    Types of Collagen

    At least 27 types based on tissue distribution and cross-linking characteristics.

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    Study Notes

    Structure-Function Relationship in Specific Proteins

    • Globular proteins exhibit a compact, rounded shape, making them water-soluble. These proteins are crucial in diverse biological processes, including enzyme activity, transport, and regulation. Examples include hemoglobin and myoglobin.
    • Fibrous proteins are insoluble in water. Their hydrophobic amino acid residues concentrate on the interior and surface, lending strength and flexibility to their structures. They form elaborate supramolecular complexes. Examples include collagen, myosin, and actin fibers.

    Globular Proteins: Hemoglobin and Myoglobin

    • Hemoglobin is an oligomeric protein (quaternary structure) whose function is to transport gases in the blood. It contains 4 polypeptide chains and 4 heme prosthetic groups, including 2 alpha and 2 beta subunits. Subunits are arranged symmetrically with non-covalent interactions.
    • Myoglobin is a monomeric protein. It stores oxygen within muscle tissue for times of intense respiration. Myoglobin's role is different from hemoglobin as it releases oxygen upon lower oxygen pressures. Both hemoglobin and myoglobin are conjugated proteins with an associated heme prosthetic group that contains iron in the ferrous state (Fe2+).

    Globular Proteins: Heme Group Structure

    • The heme group's complex organic ring structure is porphyrin.
    • The iron atom in heme has 6 coordination bonds: 4 in the plane of the porphyrin ring system, and 2 perpendicular to it.
    • The proximal histidine residue coordinates with the iron (perpendicular direction); the distal histidine residue is near the iron (but not directly bonded), and is important to regulate oxygen binding and preventing carbon monoxide binding.
    • Iron is protected from oxidation within a hydrophobic pocket of the apoprotein. This pocket also prevents CO from binding.

    Agents Affecting Oxygen Binding in Hemoglobin

    • Protons (H⁺) and carbon dioxide (CO2), waste products from cellular respiration, lower hemoglobin's affinity for oxygen as both molecules are released to tissues.
    • 2,3-bisphosphoglycerate (BPG) is an important physiological adaptation to high altitude. Decreased affinity for oxygen, increasing oxygen release to tissues.

    Allosteric Properties

    • Allosteric proteins, like hemoglobin, typically have multiple subunits with multiple ligand-binding sites, enabling a change in conformation when a ligand binds at one site. This affects ligand binding at another site.
    • The binding of the first oxygen molecule to hemoglobin shifts the structure leading to enhanced oxygen binding to the other subunits in the molecule. This facilitates an effective transport mechanism of oxygen.

    Fibrous Proteins: Collagen

    • Collagen is insoluble in water, comprised of primarily glycine, proline, and hydroxyproline amino acids. Its secondary structure is a left-handed helix.
    • Its triple helix of polypeptide chains forms tropocollagen. Tropocollagen molecules aggregate to form collagen fibers that provide strength to various connective tissues, such as tendons, cartilage, bone, and the cornea of the eye.
    • Cross-linking of collagen fibers, facilitated by covalent bonds, increases with age, making tissues more rigid.

    Fibrous Proteins: Myosin

    • Myosin is a six-subunit protein containing two heavy chains and two light chains.
    • Its carboxyl terminus is associated with a region of extended alpha-helix structure and a left-handed supercoiled helix. A globular domain contains the site where ATP is hydrolyzed.
    • The light chains are associated with the globular domains. Myosin is a key component in muscle contraction, thick filaments, which are composed of multiple myosin molecules.

    Fibrous Proteins: Actin

    • Actin is a monomeric (G-actin) protein that polymerizes into a filamentous (F-actin) structure, which is right-handed.
    • Thin filaments are composed of F-actin, troponin, and tropomyosin. Each actin monomer tightly binds to a myosin head group, which is a key element in muscle contraction and regulation.

    Fibrous Proteins: Collagen Types

    • Different collagen types (at least 27) have different tissue distributions and functions based on their structural differences, particularly the degree and presence of covalent cross-links.
    • Various collagen types support the structure and function in numerous tissues, ensuring flexibility, structure, and resistance to stress.

    Diseases Associated with Collagen

    • Osteogenesis imperfecta is a genetically-based disorder characterized by brittle bones prone to fractures.
    • Scurvy, caused by a lack of vitamin C, affects the proper formation of hydroxyproline in collagen, affecting the stability of the triple helix structure and leading to a variety of connective tissue disorders.

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    Structure-Function Relationship in Specific Proteins PDF

    Description

    Explore the distinct roles and structures of globular and fibrous proteins. Delve into specific examples like hemoglobin and myoglobin, and understand their significance in biological processes. This quiz emphasizes the differences between protein types and their functional implications.

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