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Cell Signaling and Phosphorylation in General Biology

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  • What enzyme cleaves PIP₂ in cell signaling?

    Activated phospholipase C cleaves the membrane phospholipid PIP₂ to produce IP₃ and diacylglycerol.

  • What are the two products of PIP₂ cleavage by phospholipase C?

    IP₃ (inositol triphosphate) and diacylglycerol.

  • What role does IP₃ play after being produced from PIP₂ cleavage?

    IP₃ travels through the cytosol and binds IP₃-gated calcium channels in the ER membrane, releasing Ca²⁺ into the cytosol.

  • Where does calcium released by IP₃-gated channels come from?

    Calcium is released from the lumen of the endoplasmic reticulum (ER) into the cytosol.

  • What happens to diacylglycerol after PIP₂ cleavage?

    Diacylglycerol remains in the membrane and helps activate conventional protein kinase C along with calcium.

  • How does calcium contribute to protein kinase C activation?

    Calcium, together with diacylglycerol, helps activate conventional protein kinase C.

  • What is the role of calcium binding to calmodulin?

    Calcium binding to calmodulin regulates other target proteins in the cell.

  • What is the function of protein kinases in cell signaling?

    Protein kinases transfer phosphate groups, usually from ATP, to target proteins, which can activate or inhibit them.

  • What is the role of protein phosphatases in signaling pathways?

    Protein phosphatases remove phosphate groups and help reset signaling components.

  • What can happen if phosphatase activity is lost in a signaling pathway?

    Loss of phosphatase activity can prolong phosphorylation-dependent signaling, affecting the pathway's duration.

  • Name some mechanisms that terminate cell signaling pathways.

    Ligand removal, receptor inactivation, GTP hydrolysis, cAMP degradation, and restoration of low cytosolic calcium.

  • How does phosphorylation affect target proteins?

    Phosphorylation can either activate or inhibit a protein depending on the target.

  • What molecule usually donates the phosphate group in phosphorylation?

    ATP usually donates the phosphate group transferred by protein kinases.

  • What triggers calcium release from the ER in the phospholipase C pathway?

    IP₃ binding to IP₃-gated calcium channels in the ER membrane triggers calcium release.

  • Why is restoration of low cytosolic calcium important in signaling termination?

    It helps terminate calcium-dependent signaling by returning calcium levels to baseline.