Chapter 15 | Cell to Cell Communication

Main stages of cell signaling

• Signal is sent

• Reception

• Transduction

• Response

Signal transduction

The signal is relayed to the inside of the cell and emanated throughout the cell via a signal transduction cascade

Response types

• Alter metabolism

• Alter gene expression

• Alter cell shape or movement

Rate of response

Varies between fast (less than 1 second) and slow (minutes to hours)

Different signals & cells

The same signal can have different effects in different cells, and different signals can lead to the same responses

Signal integration

Plus, cells integrate multiple simultaneous signals and are usually always bound to survival signals

Graded response

An increase in signal leads to a more gradual/proportional response. In multicellular organisms, this can happen because each cell has a graded response at once, or because individual cells respond in an all-or-none fashion with higher concentrations activating more cells

All or none response

Cells will respond completely or not at all

Gap-junction signaling

Signals are shared directly through joined gap junctions, which act as bridged tunnels between cells that physical molecules can move through

Negative feedback

Inhibits the response once it is enough or finished

Positive feedback

Increases the response so that more product is made

Paracrine signaling

From nearby cells

Endocrine signaling

From far away using hormones

Synaptic signaling

From neurons to other neurons, muscles, or glands (using neurotransmitters)

Contact-dependent signaling

Via direct ligand/receptor interactions between adjacent cells

Hydrophobic signals

Diffuse through the membrane; receptors are intracellular (often acting as transcription factors to regulate gene expression)

Hydrophilic signals

Cannot cross the membrane easily; receptors are cell-surface receptors on the plasma membrane

Cell-surface receptors

• Ion-channel coupled receptors (Ligand-gated channels)

• G-Protein coupled receptors (GPCRs)

• Enzyme-coupled receptors