Final answer:
The correct order in the MAP kinase pathway is RAS-RAF-MEK-ERK. This pathway is vital for regulating cell responses like division and differentiation, and mutations in its components can lead to cancer. ERK's activation is pivotal for initiating protein synthesis within the cell. Option D.
Step-by-step explanation:
In the MAP kinase pathway, the correct order of components is RAS-RAF-MEK-ERK. This signaling cascade commences with RAS, a small G-protein, becoming activated.
After activation, RAS then activates RAF, a MAP kinase kinase kinase (MAPKKK), which then phosphorylates MEK, known as MAP kinase kinase (MAPKK).
Subsequently, MEK phosphorylates ERK, the MAP kinase (MAPK). Once activated, ERK can enter the nucleus and trigger a cellular response such as cell division, proliferation, or differentiation.
It is crucial to understand that the MAP kinase pathway is a tightly regulated phosphorylation cascade. Aberrations in this pathway, such as a gain of function mutation in the RAS protein or a loss of function mutation in genes for the MAPK kinase pathway, can lead to uncontrolled cell proliferation, often resulting in cancer.
For example, alterations in the RAS protein's activity are implicated in roughly 30% of all cancers due to their contribution to uncontrolled cell division.
The culminating steps of this pathway involve ERK's role in protein synthesis, where phosphorylated ERK activates MNK1, which then phosphorylates the eIF-4E initiation factor essential for mRNA unfolding and the commencement of protein synthesis within the nucleus.
So Option D is correct answer.