Signaling text book summary

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From Molecular Biology of the Cell - Cell Communication Chapter


Contact-dependent signaling

development and immune system p833

local mediators (paracrine signaling)

p834

  • signals don't travel far
  • soon taken up
  • rapidly destroyed
  • immobilised

long distance signals - nervous system

p834

  • nerve cell - electric impulses (action potentials) fast (up to 100m/s)
  • neurotransmitters
  • chemical synapses

see chapter 11 for synaptic signaling processes.

Long distance signals - hormones for endocrine cells

  • transported via the bloodstream
  • slow acting

low concentration -> large effects.


Autocrine signaling

  • Cell secretes a signal that can bind back to its own receptors or those of the same cell type.
  • For example in development this is used to maintain cell identity after initial differentiation.
  • Also used to make sure all adjacent cells differentiate in the same way.

Gap junctions

  • Allows cell to communicate with each other by having a tunnel across the plasma membrane
  • Dye can squirt through the tunnels and this is how people spot them experimentally.
  • Patterns of making and breaking gap junctions are important in development.

Nitrous Oxide

  • NO and CO and other similar small hydrophobic molecules are able to pass straight through the membrane and are used as signals.
  • These bind to intracellular receptor proteins.
  • e.g. steroid hormones, thyroid hormones, retinoids, vitamin D.
  • The signal molecules bind to the receptor molecules, which then become activated, and are able to bind to DNA to regulate transcription.
  • The receptors are all members of the nuclear receptor super family.
  • This leads to the primary and secondary response:


Signaling to control gene expression - Primary response

  • ligands bound by hormones bing to gene regulatory bits and turn on expression.
  • This takes about 30 minutes

Signaling to control gene expression - Secondary response

  • Protein products made in the primary response activate other genes to produce a delayed secondary response.

N.B. This means that a simple hormonal trigger can produce a very complex pattern of gene expression.

Cell surface receptor proteins

3 kinds:

1) Ion-channel linked cell surfacce receptor proteins

N.B. these are the transmitter-gated ion channels that were updated in the transport overhaul. The top level term is already in place. p842

2) G-Protein linked cell surface receptor proteins

3) Enzyme linked cell surface receptor proteins

  • Mostly to do with the protein kinases.
  • Ligand-binding enables phosphorylation of specific proteins in target cell.


First Messengers

These are extracellular signals p843

Second messengers

  • These are small intercellular signaling molecules
  • They diffuse to membrane or cytosol depending on solubility.


Some general features in signaling

  • Cells are bathed in hundreds of different signals all the time.
  • response of different cells to the same signal can be depend on the internal machinery, even if the receptor is the same.
  • some effects on cell are permenant due to cell memory - though this is usually not the case. (chap 7 + 21)
  • half life is important as signal concentration cannot change quickly if the signal is not broken down quickly.
  • e.g. if phosphorylation is an important part of signaling then there must also be rapid dephosphorylation to keep background signal level low.
  • speed of response of a cell also depends on turnover of internal chemical (p837-838).