Cell signalling

  • The transfer of information from one cell to another. also called cell-cell signalling and intercellular communication

  • Essential part of many biological processes

  • It controls the inner workings of organisms allowing them to respond, adapt and survive

    What happens when cell communication goes wrong

  • losing the signal- type 1 diabetes

  • When signal does not reach the target- MS multiple sclerosis

  • when the target ignores the signal- type 2 diabetes

  • too much signal- excitotoxicity

  • Multiple breakdowns- cancer

Main principles of cell signalling

  1. Arrival of signal

  2. Perception of the signal by receptors

  3. Transmission of the signal by the receptor to the cell

  4. Passing on the message- signal transduction

  5. The arrival of the message at the final destination

  6. A response by the cell

Commonly seen changes

  • An alteration of the concentration of intracellular molecule such as cAMP or cGMP

  • Changes in the activity of a protein- enzymes

  • Changes in the conformation of a protein

  • Changes in the location of a molecule

  • Changes in gene expression

A good signal

  • A signal should be able to be made, mobilised and altered relatively quickly

Mechanism of intercellular communication

  • direct communication through gap junction or through recognition of surface markers

  • Indirect communication through chemical signals

Direct communication through gap junction

  • composed of membrane proteins — connexions

  • Link cytosol of 2 adjacent cells

  • Particles movement between cells act as signal

  • Communication is direct

  • Common in smooth and cardiac muscles

receptor-ligand signalling

Signal molecule remains bound to cell surface

Influences only cells that contact it

Important in development, immune response

Indirect communication through chemical signals

  • messenger is produced by source cell

  • messenger is transported to target

  • Target cell has receptor for messenger

  • Binding of messenger to receptor triggers a target cell response

  • Communication is indirect

Four forms of indirect intercellular signalling

Endocrine signalling- release of chemical messenger known as hormones. travel in the bloodstream. travel to a distant target cells, INSULIN, OESTROGEN, THYROXIN

Paracrine signalling- source cells release signal - effect neighbouring cell only affect adjacent cells- HISTAMINE

Autocrine signalling- source cell and target cell are the same - chemical messenger affects its own cell- CYTOKINES, GROWT FACTOR

Neurocrine signalling/synaptic- neuron release neurotransmitter at synapse- effect cell as end of synapse- ACETYLCHOLINE, GLYCINE, SEROTONIN

Chemical messengers can be classified by chemical properties

Lipophobic ligand

  • Not lipid soluble, is water soluble

  • Does not easily cross cell membrane require pumps/channels

  • Receptors on cell membrane

  • General action of target response- enzyme activation, membrane permeability changes

Lipophilic ligand

  • lipid soluble not water soluble

  • easily diffuse across membrane

  • Receptor location within cell

  • General action of target response via gene activation

How a chemical signal is translated

  • messenger bonds to receptors

  • Binding results in cell response

  • Signal transduction- process of producing response in target- amplification of the signal

cell signalling in correct order

Receptor binding

  • specificity

  • Binding is brief and reversible

  • Affinity= strength of binding

  • Location of binding - lipophobic= cell membrane lipophilic= within cell

  • One messenger may bind to many receptor types

  • One target may have many types of receptors

  • Number of receptors per cell varies and is dynamic