Page 36 - Cell biology PDG 2024

2) Paracrine signaling: here a secretion of a ligand occurs from one cell
but acts on a neighboring target cell
The secreted growth factor diffuses over a short distance and thus they
are considered local mediators of cell communication and they act for a
short period of time
EX: the transfer of signals across synapses between nerve cells
3) Endocrine signaling: it occurs when endocrine cells release hormones
that act on distant target cells in the body producing a slower, long-
lasting response
Ex: Hormones travel the large distances between endocrine cells and
their target cells via the bloodstream
4) Direct contact signaling: ex: Gap junctions in animals and
plasmodesmata in plants are channels between the plasma membranes
of neighboring cells. These channels allow small signaling molecules,
called intracellular mediators, to diffuse between the two cells. Small
molecules, such as calcium ions (Ca2+), are able to move between cells,
but large molecules, like proteins and DNA, cannot fit through the
channels
The specificity of these channels make sure that the cells remain
independent, but can quickly and easily transmit signals. This rapid
transfer of signaling molecules helps communicating the current state of
the cell with the target cell next to it; this allows a group of cells to
coordinate their response to a signal that only one of them may have
received

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