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3.Hemoglobin
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Flashcards in this deck (10)

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  • What is the basic structure of adult hemoglobin?

    • Four subunits: α₂β₂
    • Each subunit binds one O₂ at Fe²⁺
    hemoglobin structure

  • Name two non‑O₂ molecules that bind to hemoglobin and one function of H⁺ binding.

    • CO₂ → carbaminohemoglobin
    • 2,3‑BPG → decreases O₂ affinity
    • H⁺ → acts as a buffer
    hemoglobin binding

  • What is the role of \(2,3\)‑BPG in red blood cells?

    • Decreases hemoglobin's affinity for O₂, promoting O₂ unloading
    • Produced in RBCs from glycolysis intermediate
    2,3-bpg rbc

  • Which conditions cause a right shift of the O₂–hemoglobin dissociation curve (promoting unloading)?

    • Decreased pH
    • Increased temperature
    • Increased CO₂
    • Increased 2,3‑BPG
    dissociation-curve right-shift

  • Which conditions cause a left shift of the O₂–hemoglobin dissociation curve (increasing affinity)?

    • Increased pH
    • Decreased temperature
    • Decreased CO₂
    • Decreased 2,3‑BPG
    • HbF
    dissociation-curve left-shift

  • What does the Bohr effect describe?

    • CO₂ and H⁺ in tissues decrease hemoglobin's O₂ affinity, promoting O₂ unloading
    bohr physiology

  • What does the Haldane effect describe?

    • O₂ in the lungs decreases hemoglobin's affinity for CO₂, promoting CO₂ release
    haldane physiology

  • How does fetal hemoglobin (HbF) differ from adult hemoglobin?

    • Composition: α₂γ₂
    • Higher O₂ affinity (left-shifted) because γ subunits lack 2,3‑BPG binding sites
    hbf fetal

  • Why is myoglobin considered a final O₂ reserve in muscle?

    • Single O₂ binding site, high O₂ affinity (left-shifted), supplies O₂ during hypoxia
    myoglobin muscle

  • What is the effect of hydroxyurea relevant to hemoglobin?

    • Induces HbF formation, used to treat sickle cell disease
    hydroxyurea therapy
学习笔记

Hemoglobin — structure & primary function

  • Definition: Hemoglobin (Hb) is the red blood cell protein that transports O₂ and helps carry CO₂/H⁺.
  • Structure: Tetrameric protein \(\alpha_2\beta_2\) (adult Hb); each subunit binds one O₂ at an iron center \(Fe^{2+}\).
  • Other bindings: CO₂ forms carbaminohemoglobin; H⁺ is buffered by Hb; \(2,3\)-BPG binds Hb and lowers O₂ affinity.
  • \(2,3\)-BPG: Produced in RBCs from glycolysis intermediates; increases with chronic hypoxia and promotes O₂ unloading.

Oxygen–hemoglobin dissociation curve (O₂–Hb curve)

  • Shape & cooperativity: Sigmoidal curve due to cooperative O₂ binding across subunits; small PO₂ changes near physiological range cause large saturation changes.
  • Right shift (promotes O₂ unloading): Caused by ↓pH (↑H⁺), ↑temperature, ↑CO₂, and ↑\(2,3\)-BPG; clinically means tissues get more O₂.
  • Left shift (promotes O₂ loading): Caused by ↑pH, ↓temperature, ↓CO₂, ↓\(2,3\)-BPG, and presence of HbF; increases Hb O₂ affinity and reduces tissue unloading.
  • Bohr effect: Local ↑CO₂ and H⁺ in tissues lower Hb affinity for O₂ (right shift), aiding O₂ release where needed.
  • Haldane effect: In the lungs, O₂ binding to Hb reduces Hb affinity for CO₂ and H⁺, facilitating CO₂ release.

Fetal hemoglobin (HbF)

  • Composition: \(\alpha_2\gamma_2\).
  • Functional consequences: Higher O₂ affinity (left-shifted curve) because the γ subunits bind \(2,3\)-BPG poorly, promoting O₂ transfer from maternal blood to fetus.
  • Clinical note: Hydroxyurea can induce HbF production and is used to treat sickle cell disease.

Myoglobin

  • Role: O₂ storage in muscle; provides reserve in hypoxia.
  • Properties: Single O₂ binding site (no cooperativity) and higher O₂ affinity than Hb (left-shifted), so it extracts O₂ from blood at low PO₂.

Key practical points for students

  • Remember the major factors shifting the O₂–Hb curve: pH, temperature, CO₂, and \(2,3\)-BPG.
  • Right shift = easier unloading to tissues; left shift = tighter O₂ binding (less unloading).
  • Distinguish Bohr (CO₂/H⁺ effect on O₂ binding) from Haldane (O₂ effect on CO₂ binding).
  • Hb composition matters: adult Hb \(\alpha_2\beta_2\), fetal Hb \(\alpha_2\gamma_2\), myoglobin single subunit.

Quick summary bullets

  • Hb structure: \(\alpha_2\beta_2\), O₂ binds \(Fe^{2+}\).
  • \(2,3\)-BPG lowers O₂ affinity; increases in chronic hypoxia.
  • Bohr effect (tissues): ↑CO₂/H⁺ → right shift; Haldane (lungs): O₂ binding → CO₂ release.
  • HbF: \(\alpha_2\gamma_2\), higher affinity; therapeutic induction by hydroxyurea.
  • Myoglobin: single site, high affinity O₂ store.