Calcium Homeostasis and Transport
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Questions and Answers

What are the primary functions of Ca2+ -ATPases in cells?

  • Regulating neurotransmitter release
  • Facilitating the storage of calcium in mitochondria
  • Maintaining basal Ca2+ levels (correct)
  • Converting ATP to ADP
  • Which of the following correctly describes the role of Na+/Ca2+ exchangers?

  • They help to remove calcium from cells against its gradient. (correct)
  • They facilitate the entry of calcium during muscle contraction.
  • They primarily store calcium in the nucleus.
  • They are involved in the production of IP3.
  • What are the key signaling molecules produced by GPCRs that affect calcium release?

  • cAMP and cGMP
  • Nitric oxide and cyclic AMP
  • Calmodulin and CaM kinase
  • IP3 and DAG (correct)
  • How do STIM and Orai receptors contribute to calcium homeostasis?

    <p>By regulating membrane calcium flow</p> Signup and view all the answers

    Which process is NOT influenced by intracellular calcium signaling?

    <p>DNA replication</p> Signup and view all the answers

    What cellular process is directly affected by the level of intracellular calcium?

    <p>Cell apoptosis</p> Signup and view all the answers

    Which of the following is NOT a role of calcium in cellular functions?

    <p>Absorption of nutrients in the digestive tract</p> Signup and view all the answers

    Which scientists provided early evidence for the role of calcium in neurotransmission?

    <p>Ringer and Locke</p> Signup and view all the answers

    How many Ca2+ ions are moved out of the cell for each ATP hydrolyzed by PMCA?

    <p>1 Ca2+</p> Signup and view all the answers

    Which protein enhances the activity of PMCA through binding?

    <p>Calmodulin</p> Signup and view all the answers

    What is the function of SERCA in muscle cells?

    <p>Moves Ca2+ into the sarcoplasmic reticulum</p> Signup and view all the answers

    Which of the following describes the states of SERCA?

    <p>E1 – high calcium affinity, E2 – low calcium affinity</p> Signup and view all the answers

    Which gene encodes the NCX protein?

    <p>SLC8</p> Signup and view all the answers

    Which subfamily of voltage-gated Ca2+ channels includes L-type channels?

    <p>Cav1</p> Signup and view all the answers

    The calcium release from intracellular stores is primarily mediated by which receptor?

    <p>Inositol 1,4, 5-trisphosphate receptor (IP3R)</p> Signup and view all the answers

    Which of the following statements regarding NCX isoforms is correct?

    <p>NCX1 is ubiquitously expressed while NCX2 and NCX3 are specific to brain and skeletal muscle</p> Signup and view all the answers

    What is the typical free cytoplasmic calcium concentration ([Ca2+i]) in cells?

    <p>0.1 µM</p> Signup and view all the answers

    Which protein is known for its calcium-binding ability and contains the EF-hand motif?

    <p>Calmodulin</p> Signup and view all the answers

    What type of calcium transport system transfers calcium across membranes after muscle contraction?

    <p>Ca2+-ATPases</p> Signup and view all the answers

    Which of the following statements about PMCA and SERCA is true?

    <p>SERCA transports calcium in a 2:2 ratio with H+.</p> Signup and view all the answers

    Which of the following serves as a specialized channel for calcium entry into cells?

    <p>L-type calcium channels</p> Signup and view all the answers

    What is the function of calsquestrin in muscle cells?

    <p>To bind calcium in the sarcoplasmic reticulum</p> Signup and view all the answers

    Which of the following mechanisms is NOT involved in moving calcium into cells?

    <p>Facilitated diffusion via glucose channels</p> Signup and view all the answers

    How do calcium buffering proteins help in cellular functions?

    <p>By sequestering free calcium and reducing fluctuations.</p> Signup and view all the answers

    What structural form do IP3 receptors (IP3R) take?

    <p>Tetramers of 4 transmembrane spanning helices</p> Signup and view all the answers

    What role do STIM1 proteins serve during store-operated calcium entry (SOCE)?

    <p>They translocate to ER/SR-PM upon calcium store depletion</p> Signup and view all the answers

    Which proteins are involved in store-operated calcium entry?

    <p>STIM1 and Orai1</p> Signup and view all the answers

    What happens to STIM1 proteins upon calcium store-depletion?

    <p>They undergo oligomerisation and translocate</p> Signup and view all the answers

    What is the main consequence of mutations in STIM1?

    <p>Increased store-operated calcium entry</p> Signup and view all the answers

    Where is most intracellular calcium primarily found?

    <p>Bound by calcium-binding proteins in organelles</p> Signup and view all the answers

    Which channel type is NOT involved in calcium transport?

    <p>Voltage-gated potassium channels</p> Signup and view all the answers

    What is the function of Ca2+ ATPases?

    <p>To actively transport calcium ions out of the cell</p> Signup and view all the answers

    Study Notes

    Calcium Homeostasis

    • Calcium is essential for a variety of cellular functions, including neurotransmitter and hormone release, muscle contraction, cell excitability, and protein synthesis.
    • Calcium homeostasis involves precise regulation of calcium concentrations both inside and outside of cells.
    • Extracellular calcium concentrations are around 1mM.
    • Intracellular calcium concentrations are around 0.1μM.
    • Calcium-binding proteins like calmodulin, S100 proteins, and calcineurin bind to calcium directly.
    • Calcium-buffering proteins like calnexin and calsquestrin work together to store calcium within intracellular organelles.

    Calcium Transport

    • Points of Entry for Calcium
      • Ca2+-ATPases:
        • PMCA (Plasma Membrane Ca2+ ATPase) moves calcium outside the cell, using ATP.
        • SERCA (Sarcoplasmic Reticulum Ca2+ ATPase) moves calcium into the sarcoplasmic reticulum, using ATP..
      • Voltage-gated Ca2+ Channels
        • L-type Ca2+ channels play a key role in calcium influx.
      • Na+/Ca2+ exchanger (NCX):
        • NCX1, NCX2, and NCX3 exchange calcium ions for sodium ions.
      • Permeability Transition Pore
      • Influx Mechanisms: Various pumps, exchangers, and channels are involved in moving calcium into and out of cells, including different organelles.
    • Other Important Calcium Signaling Molecules:
      • IP3 (inositol 1,4, 5-trisphosphate): This molecule activates IP3 receptors in the endoplasmic reticulum (ER), leading to calcium release from ER stores.
        • IP3 receptors are tetramers with four transmembrane domains.
      • STIM1: This protein senses changes in ER luminal calcium levels.
      • Orai1: This protein interacts with STIM1, enabling calcium influx from the extracellular space.
    • Store-Operated Calcium Entry (SOCE): A process by which depletion of calcium from intracellular stores leads to calcium influx from the extracellular space.
      • SOCE is essential for maintaining continuous calcium signaling in cells.
      • Mutations in STIM1 can lead to increased SOCE.

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    Description

    Explore the essential roles of calcium in cellular functions, including neurotransmitter release, muscle contraction, and protein synthesis. This quiz covers the mechanisms of calcium homeostasis and the various transport proteins involved in regulating calcium levels in cells.

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