Question

trace the steps of a long and indirect signaling pathway from a cell-surface receptor to a change in gene expression in the nucleus . compare this pathway with an example of a short and direct pathway from cell-surface to the nucleus.

Answer 1

There is two kinds of ligand molecules, hydrophilic large signaling ligands, and hydrophobic small ligands. For the large hydrophilic signaling ligands, there are different kinds of cell surface receptors present with which the ligands bind leading to a conformational change on the cytoplasmic domain of the receptor triggering the downstream signaling pathway. In the downstream signaling pathway, usually, a second messenger is generated which upon binding to specific protein kinase phosphorylate and activate a transcription factor which will go inside the nucleus and regulate the expression of a specific gene or a specific set of genes. (long and indirect pathway).

But, for the small hydrophobic ligands molecule, as they can easily pass through the plasma membrane, a specific kind of cytoplasmic receptors presents which upon binding with the ligand molecule transported inside the nucleus regulate the expression of a specific set of genes. (short and direct pathway).