Cell Communication and Signaling

Study Notes

Cells communicate primarily through chemical signals, sending and receiving messages.
In multicellular organisms, communication between cells allows for coordination and regulation of various processes, such as growth, development, and response to environmental changes.
Autocrine signaling occurs when a cell releases a signal that binds to receptors on the same cell.
Contact-dependent signaling requires direct physical contact between cells for communication.
Paracrine signaling involves signaling between nearby cells, where the signal diffuses through the extracellular space.
Endocrine signaling occurs when signaling molecules, known as hormones, are released into the bloodstream and travel long distances to reach target cells.
Growth factors are signaling molecules that stimulate cell growth and division.

Non-polar signaling molecules, like steroid hormones, can directly cross the cell membrane and bind to intracellular receptors.
Polar signaling molecules, like peptide hormones, bind to transmembrane receptors, which span the cell membrane.
G protein-coupled receptors (GPCRs) are a major class of transmembrane receptors, often involved in short-term responses.
- Activation: Binding of a signaling molecule causes a conformational change in the receptor, activating a G protein located on the inner side of the membrane.
- Amplification: Activated G protein triggers a cascade of events, involving second messengers like cAMP, leading to signal amplification.
- Termination: Signal is terminated by various mechanisms, such as inactivation of the G protein, breakdown of second messengers, or desensitization of the receptor.

Receptor kinase activation often leads to long-term responses, such as changes in gene expression and cell growth.
Receptor kinases are transmembrane receptors that have enzymatic activity, often phosphorylating target proteins.
MAP kinase pathway is a common signaling pathway activated by receptor kinases.
- Activation: Signaling molecules bind to receptor kinases, initiating a cascade of phosphorylation events that ultimately activate MAP kinases.
- Signal integration: Different signaling pathways can converge on the MAP kinase pathway, allowing for integration of multiple signals.
Mutations in receptor kinases can lead to uncontrolled cell growth and cancer.
- Example: Mutations in the Kit receptor kinase, a receptor involved in cell growth and development, can lead to various cancers like mastocytosis.

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