CELL SIGNALING

What is Cell Signaling?

• Series of steps that allow cells to respond to signals from their environment

• Cells will respond by initiating some sort of cellular activity

  • e.g. initiation of Cell Cycle

• Usually requires the secretion of a ligand (chemical signal) from the initiating cell that travels to the target cell

• Only cells that have a correct receptor protein will react to the signal molecule (ligand)

Basics of Cell Signaling

• Step 1: Reception

  • Ligand binds to receptor

  • Receptor changes shape

  • Shape change transmits signal inside of the cell

• Step 2: Transduction

  • Signal is moved from the cell membrane to the nucleus through phosphorylation of a series of proteins

    • Adding a protein

• Step 3: Response

  • Final molecule in signal pathway initiates transcription of target genes in the nucleus

    • Writes it down basically

  • Leads to a protein being made which causes a cell response

2 Mechanisms of Ligand Delivery

• Cell to Cell Contact

  • Cells make physical contact to transmit signals and initiate cell response

  • Target cell expresses a receptor protein on its cell membrane’

    • Allows for cell recognition

  • Requires direct contact between signal and receptor proteins bound on the cell membrane of communicating cells

• Paracrine Signaling

  • Communicating cell releases a ligand (signaling molecule) that moves to the target (receiving cell)

  • Ligands can travel short distances thru diffusion or long distances thru the bloodstream

Mechanisms of Cell to Cell Contact

• Fastest means of transmitting a signal

• Gap Junctions

  • Only in animal cells

  • Cell membranes fuse and open pores between two cells

  • Allows signals to quickly diffuse and initiate cell response

• Plasmodesmata

  • Only in plant cells

  • Pores open between cell membrane/cell wall of two cells

  • Allows signals to quickly diffuse and initiate cell response