Despite the protective membrane that separates a cell from the environment, cells need the ability to detect and respond to environmental changes. Additionally, cells often need to communicate with one another. Unicellular and multicellular organisms use a variety of cell signaling mechanisms to communicate with the environment.
Cells respond to many types of information, often through receptor proteins positioned on the membrane. For example, skin cells respond to and transmit touch...

Despite the protective membrane that separates a cell from the environment, cells need the ability to detect and respond to environmental changes. Additionally, cells often need to communicate with one another. Unicellular and multicellular organisms use a variety of cell signaling mechanisms to communicate with the environment.
Cells respond to many types of information, often through receptor proteins positioned on the membrane. For example, skin cells respond to and transmit touch...

Signaling cascades usually lack linearity. Multiple pathways interact and regulate one another, allowing cells to integrate and respond to diverse environmental stimuli.
Convergence and divergence, and cross-talk between signaling pathways
Two distinct signaling pathways can converge on a single functional unit, which may either be a single protein or a complex of proteins. The response is either functionally distinct or synergistic between the two pathways but different from the response...

When a ligand binds to a cell-surface receptor, the receptor's intracellular domain changes shape, which may either activate its enzyme function or allow its binding to other molecules. The initial signal is amplified by most signal transduction pathways. This means that a single ligand molecule can activate multiple molecules of a downstream target. Proteins that relay a signal are most commonly phosphorylated at one or more sites, activating or inactivating the protein. Kinases catalyze the...

In multicellular organisms, many molecules transmit signals between cells to pass information. These signals vary in complexity and include small peptides, nucleotides, steroids, fatty acid derivatives, and dissolved gases such as nitric oxide. Some signaling molecules diffuse through the plasma membrane to act locally between neighboring cells or travel long distances. Others remain attached to the cell surface, transmitting information to other cells only when they make contact. In some...

In multicellular organisms, many molecules transmit signals between cells to pass information. These signals vary in complexity and include small peptides, nucleotides, steroids, fatty acid derivatives, and dissolved gases such as nitric oxide. Some signaling molecules diffuse through the plasma membrane to act locally between neighboring cells or travel long distances. Others remain attached to the cell surface, transmitting information to other cells only when they make contact. In some...