Final answer:
When a signal triggers changes in gene expression, it directs the cell towards specific responses or actions.
Step-by-step explanation:
The initiation of a signaling pathway in a cell is triggered by a signal, either from the external environment or from within the cell itself. This signal leads to changes in the expression of genes, which direct the cell towards specific responses or actions. The responses can include protein synthesis, changes in cell metabolism, cell growth, or even cell death.
For example, when a signal transduction pathway is activated in muscle cells, it allows them to respond to the immediate energy requirement by converting glycogen or fat into glucose. On the other hand, uncontrolled cell growth, caused by mutations in the genes encoding protein components of signaling pathways, can lead to cancer.
Overall, the initiation of a signaling pathway and subsequent changes in gene expression help the cell respond and adapt to its environment.