Answer:
The main difference between the signal transduction pathway and the steroid hormone pathway is the type of signaling molecule involved and the mechanism by which they transmit their signals within the cell.
In the signal transduction pathway, the signaling molecules are typically large, polar, and water-soluble molecules such as hormones, growth factors, and neurotransmitters. These molecules cannot cross the plasma membrane of the cell, so they bind to a receptor on the cell surface, which triggers a series of intracellular signaling events that eventually lead to a cellular response.
In contrast, the steroid hormone pathway involves small, non-polar, and lipid-soluble molecules such as steroids (e.g. testosterone, estrogen, cortisol). These molecules can easily cross the plasma membrane of the cell and bind to a receptor inside the cell, often in the cytoplasm or nucleus. This binding event typically triggers a change in the conformation of the receptor, which allows it to bind to DNA and regulate gene expression directly, resulting in a cellular response.
So, while both pathways involve signaling molecules and receptors, the main difference is the type of signaling molecule involved and the mechanism by which they trigger a cellular response.