Which of the following best describes/true regarding the RAS gene?

INI-CET EXAM -2025

Pathology & Genetics (E5)

Medium

Appeared in: INI-CET EXAM -2025

Explanation

The RAS gene encodes a GTP-binding protein (a small G-protein) that acts as a molecular switch in cell signaling.
Point mutations in the RAS gene are common in cancer and lead to a loss of its intrinsic GTPase activity.
This traps the RAS protein in a constitutively active, GTP-bound state.
The constantly active RAS protein continuously stimulates downstream pro-growth pathways, most notably the MAP kinase (MAPK) cascade, leading to uncontrolled cell proliferation.

Option B: This statement is factually incorrect and contradictory. Enhanced DNA repair leads to genomic stability, not instability. Also, RAS is a signaling protein, not a DNA repair enzyme.
Option C: This describes the mechanism of a tumor suppressor gene, but RAS is a proto-oncogene. Proto-oncogenes cause cancer through gain-of-function mutations (activation), whereas tumor suppressor genes cause cancer through loss-of-function mutations (inactivation).
Option D: This describes a different, albeit related, oncogenic mechanism. While RAS is downstream of tyrosine kinase receptors (TKRs), the question is about the RAS gene itself. Activating mutations in RAS are a separate event from the amplification of TKR genes.

Visual 1: Diagram - A flowchart showing the RAS/MAPK signaling pathway. It should depict a growth factor binding to a receptor, activating RAS (switching from GDP to GTP), which then activates the RAF-MEK-ERK (MAPK) cascade, ultimately leading to transcription and cell proliferation. A second version should show a mutated, constitutively active RAS bypassing the need for a growth factor.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The role of the RAS proto-oncogene in cancer pathogenesis as background academic context rather than a clinical decision trigger.
RAS mutations are among the most common oncogenic alterations in human cancers, found in approximately 90% of pancreatic cancers, 50% of colon cancers, and 30% of lung adenocarcinomas.
The presence of a RAS mutation has significant therapeutic implications. For example, colorectal cancer patients with KRAS mutations do not respond to anti-EGFR therapies (like cetuximab), as the mutation bypasses the need for upstream EGFR signaling.
What if? If a patient's tumor has a mutation in BRAF (a protein downstream of RAS) instead of RAS, the clinical approach changes. The patient would not benefit from a RAS inhibitor but could be a candidate for a BRAF inhibitor (like vemurafenib), especially in melanoma.

How to Approach the Question

First, identify the core subject of the question: the function of the RAS gene in a pathological context (implied by the options).
Recall or deduce the classification of RAS. It is one of the most well-known proto-oncogenes.
Analyze Option A: It describes activation of a GTP-binding protein leading to a kinase cascade. This aligns with the known function of RAS as a G-protein that activates the MAPK pathway.
Analyze Option B: It mentions DNA repair. This is a distinct cellular process. RAS is a signaling protein, so this is unlikely. The statement is also internally inconsistent (enhanced repair causing instability).
Analyze Option C: It mentions inactivation of a tumor suppressor gene. This is the opposite of what happens with a proto-oncogene like RAS, which undergoes activation.
Analyze Option D: It mentions tyrosine kinase receptors (TKRs). While RAS is linked to TKRs, this option describes TKR amplification, which is a separate mechanism. The question is about the RAS gene itself. The most direct and accurate description of RAS's role is its own constitutive activation.

Concept Tested & Keywords

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