cell signalling basics

cell signalling definition

The process whereby a change of circumstances in one cell can result in a change in the activity of another cell

signalling cell

registers stimulus and secretes a signal molecule

target cell

responds to signal molecule by changing biochemical activity

signalling molecule

molecule secreted in response to a stimulus. made quickly. amount secreted is proportional to stimulus intensity

receptor molecules

ensure only the right cells respond to the signal

gap junctions

Direct connections between cells that allow groups of cells to behave in the same way.

paracrine signalling

Signal molecules released to act on a nearby target cell (short distance; molecules may otherwise be destroyed).

autocrine signalling

a cell releases a signal molecule and also has receptors for it (e.g. cancer cells)

neuronal signalling

transmission of signals from a presynaptic cell to a postsynaptic cell via neurotransmitters

endocrine signalling

long-distance signalling using hormones released unto bloodstream. all cells exposed, but only ones with right receptor respond

3 stages of cell communication

reception, transduction, response

transduction

message passed inside cell via molecules, often with signal amplification

reception

ligand binds to specific receptor

response

altered activity of an end-point target protein

what usually initiates signal transduction?

a shape change in the receptor after ligand binding

input examples

extracellular matrix, other cells, environment, nutrient cycle, internal states (homeostasis, cell cycle)

output responses

gene expression, morphological changes, production/secretion, growth/division, cell death

3 main strategies for signal transmission across membranes

1. Passive crossing (lipid-soluble signals like NO, O₂, hormones).

2. Ion channels (protein pores allowing ion flow).

3. Transmembrane receptors (various types using different mechanisms).