什么是细胞信号传导？

Cells use a variety of signaling mechanisms to coordinate specific actions within and between cells. Intercellular signaling refers to communication between cells. Here, one cell secretes an initial signaling molecule called a ligand to induce responses in targeted cells.

Once the ligand binds, intracellular signaling occurs, referring to how a signal is processed within the cell. In some bacterial communities, a kind of intercellular signaling called quorum sensing occurs, where the cells of a community react in concert, once the concentration of a signaling ligand reaches a critical threshold. In eukaryotes, sometimes the ligand targets the cell which released it, called autocrine signaling.

When the ligand targets neighboring cells, it is known as paracrine signaling. Another form of communication, contact-dependent signaling, occurs between two cells that are physically touching. The signal passes directly from one cell to another through gap junctions in animal cells, or in plant cells connected by plasmodesmata.

Multicellular organisms often need cells in one part of the body to communicate with cells in a different part of the body. To do this, they release ligands into the bloodstream in a process called endocrine signaling. In the nervous system, neurons use a specific form of signaling that relies on specialized structures called synapses.

Here, the cells do not actually make contact, but release neurotransmitters and other molecules to communicate with our target cells. Inside the cell, the original signal is often converted or transduced when the activation of receptors sets off a chain of events called a signaling cascade. Signaling therefore often involves the detection of the signal, intermediate steps transducing the signal, and a final target eliciting a response from a cell, such as regulation of gene expression.