Final answer:
Intracellular signaling molecules facilitate communication within cells through a process initiated by ligand binding, leading to a signaling pathway involving phosphorylation, second messengers, and gene expression regulation.
Step-by-step explanation:
An intracellular signaling molecule is a form of chemical communication that occurs within a cell. Upon the binding of a ligand, which is a molecule that binds specifically to a receptor on the surface of a cell, a series of events called signal transduction is initiated. This can lead to a variety of responses such as gene expression changes or alterations in cellular activity.
During signal transduction, the ligand binding usually triggers phosphorylation, a process where kinases add phosphate groups to proteins, thereby activating or inactivating them. Additionally, second messengers, such as calcium ions (Ca²+), cyclic AMP (cAMP), diacylglycerol (DAG), and inositol triphosphate (IP3), are often involved in propagating the signal within the cell. These messengers can initiate further events in the signaling pathway, resulting in a specific cellular response.
Various intracellular signaling methods rely on enzymatic modifications to propagate the signals through the cell's cytoplasm and sometimes the nucleus as well, which often result in gene expression regulation. Hydrophobic signaling molecules can diffuse through the plasma membrane to interact with intracellular receptors, often acting as transcription factors that regulate DNA transcription in the nucleus.