& x20;What is the primary molecular mechanism by which UV light induces carcinogenesis? - INI-CET EXAM -2026

INI-CET EXAM -2026

Microbiology

Easy

Appeared in: INI-CET EXAM -2026

Explanation

Ultraviolet (UV) radiation, particularly UVB, is absorbed by DNA in skin cells.
This energy causes adjacent pyrimidine bases, most commonly two thymines, to form a covalent bond.
This structure, known as a thymine dimer (a type of cyclobutane pyrimidine dimer), creates a physical kink in the DNA strand.
This direct DNA damage is the primary and initial molecular event that, if unrepaired, leads to mutations and can initiate carcinogenesis.

Option A: The primary effect of UV damage is not to inhibit TP53. Instead, DNA damage activates the p53 protein to halt the cell cycle for repair or induce apoptosis (cell death).
Option B: Activation of the NF-kappa β pathway is primarily involved in the inflammatory response to UV exposure, which manifests as sunburn.
Option D: In a normal cellular response to DNA damage, the cell cycle is arrested to allow time for repair. This involves the inhibition of cyclin-dependent kinases (CDKs), which means cyclin activity is effectively decreased, not increased.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Molecular mechanism of UV-induced carcinogenesis as background academic context rather than a clinical decision trigger.
Understanding this mechanism is fundamental to patient education on sun safety, as it explains why sun exposure causes skin cancer.
Nurses can emphasize that sunscreen and protective clothing act as a physical barrier to prevent UV rays from reaching DNA and forming these cancer-initiating thymine dimers.
This knowledge reinforces the importance of regular skin checks for early detection of lesions that may have arisen from unrepaired DNA damage.

How to Approach the Question

First, identify the core of the question: it asks for the 'primary' molecular mechanism. This means you are looking for the very first event that happens when UV light interacts with a cell to cause cancer.
Analyze the keywords: 'UV light', 'carcinogenesis', 'primary'. This directs you to think about the initial DNA damage, not the cell's response or later consequences.
Evaluate each option in the context of a timeline: What happens first?
Option C, 'Thymine dimers', describes the direct physical damage to the DNA molecule caused by UV energy absorption. This is an immediate, primary event.
Options A, B, and D describe cellular responses (p53 activation, inflammation) or downstream consequences of mutations (cyclin upregulation). These happen after the initial DNA damage has occurred.
Therefore, the formation of thymine dimers is the most accurate answer for the 'primary' mechanism.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 1 p. 472-474

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 722-724