Final answer:
The MAPK/ERK pathway is the simplest and most direct way to transmit a signal from a cell-surface receptor to the nucleus, involving a phosphorylation cascade initiated by the binding of EGF to its receptor, leading to effects on gene expression.
Step-by-step explanation:
The simplest and most direct pathway known to transmit a signal from a cell-surface receptor to the nucleus is the MAPK/ERK pathway, also known as Ras-Raf-MEK-ERK pathway. A classicexample is when the epidermal growth factor (EGF) binds to the EGF receptor. This binding triggers a phosphorylation cascade where a series of proteins communicate the signal from the receptor at the cell surface down into the nucleus. An activated ERK, which is part of this pathway, enters the nucleus and activates a protein kinase that regulates protein synthesis by affecting the translation process. This signaling pathway demonstrates how external signals can ultimately influence gene expression and protein production inside the cell.