BIO 181 Ch11cell_communication

Cell Communication Overview

  • Chapter 11 provides an insight into how cells communicate and the mechanisms involved.

Cellular Messaging

  • Cells can signal to one another and interpret signals from their environment.

  • Most signals are chemical; an example is epinephrine (adrenaline).

Mating Types in Yeast

  • Yeast (Saccharomyces cerevisiae) has two mating types: a and α.

  • Cells recognize each other through secreted factors specific to each type.

  • Binding of a mating factor at the cell surface initiates a signal transduction pathway leading to cell fusion.

Cell Junctions and Local Signaling

  • Plasma membranes have structures that facilitate communication:

    • Gap Junctions (animal cells)

    • Plasmodesmata (plant cells)

  • Local signaling involves direct cell contact and the exchange of signals:

    • Local regulators (signaling substances) pass through cytosol to bind target cell receptors.

Types of Local Signaling

  • Paracrine Signaling:

    • Involves a signaling cell discharging local regulators to nearby target cells.

    • Example: Animal cells respond to growth factors.

  • Synaptic Signaling:

    • Occurs in the nervous system where nerve cells release neurotransmitters stimulating target cells (muscles or other nerves).

Long-Distance Signaling

  • Endocrine Signaling:

    • Specialized cells release hormones into the bloodstream.

    • Hormones travel to target cells at a distance, facilitating communication across the body.

Stages of Cell Signaling

The Three Stages:

  1. Signal Reception

  2. Signal Transduction

  3. Cellular Response

Reception

  • Signal molecules (ligands) bind to receptor proteins (usually plasma membrane proteins).

  • This binding changes the receptor's shape and initiates signal transduction.

Membrane Receptors

  • Most water-soluble signal molecules bind to:

    • G Protein-Coupled Receptors (GPCRs)

    • Receptor Tyrosine Kinases (RTKs)

    • Ion Channel Receptors

G Protein-Coupled Receptors (GPCRs)

  • Interact with cytoplasmic G proteins acting as on/off switches.

  • Modifications can affect physiology (e.g., cholera toxin impacts G protein function).

Receptor Tyrosine Kinases (RTKs)

  • Membrane receptors that attach phosphates to tyrosine residues.

  • Capable of triggering multiple signal transduction pathways simultaneously.

Ligand-Gated Ion Channels

  • Important for nervous system signaling.

  • Bind specific signaling molecules, either opening or closing to allow ions (e.g., Na+, Ca2+) through.

Second Messengers

  • After the first messenger (extracellular signal), second messengers facilitate the signaling pathway:

    • Examples include cyclic AMP and calcium ions.

  • Pathway example: Epinephrine → GPCR → G protein → adenylyl cyclase → cAMP → Protein Kinase A → Cellular Response.

Intracellular Receptors

  • Some receptors are found in the cytosol or nucleus, activated by small or hydrophobic messengers.

  • Example: Testosterone activates genes by binding to its receptor and entering the nucleus.

Transduction

  • Involves a series of steps where the binding of a signaling molecule activates a chain of molecular interactions.

  • This process can involve phosphorylation cascades using kinases with consecutive conformational changes.

Response

  • Responses occur in the cytoplasm or involve gene expression in the nucleus:

    • Final activated molecules can serve as transcription factors to turn genes on or off, affecting enzyme synthesis.