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DNA is the cornerstone of life, carrying the precise instructions that dictate the form and function of every organism—from the simplest bacteria to the most complex humans. Any alteration to its structure can disrupt these instructions and trigger disease.
The informational content of DNA is encoded in its unique sequence of four nucleotide bases—adenine (A), cytosine (C), guanine (G), and thymine (T). These bases link together to form a double‑helix strand, where the order of the bases provides the blueprint for biological processes.
Ultraviolet (UV) radiation is a high‑energy component of sunlight that, while invisible, can damage DNA. UV is categorized into three types: UVA, UVB, and UVC. UVC carries the highest energy but is largely absorbed by the Earth’s ozone layer. UVA penetrates the atmosphere but lacks sufficient energy to directly alter DNA, whereas UVB reaches the surface and possesses enough energy to cause molecular damage.
UVA does not directly break DNA strands but can generate reactive oxygen species (ROS). These ROS attack DNA, proteins, and lipids, contributing to mutagenesis and cancer risk. Indoor tanning devices that emit UVA are associated with a 75 % higher likelihood of skin cancer compared to non‑tanners. (Source: CDC)
UVB, however, directly alters DNA. When two thymine bases appear consecutively (TT) along a strand, UVB energy changes a chemical bond, causing the adjacent thymines to bond together and form a thymine dimer. These dimers distort the helix, preventing accurate reading by the cell’s replication machinery. A single second of UVB exposure can generate up to 100 dimers; excessive accumulation may trigger cell death or oncogenic transformation.
Cells possess robust repair pathways that recognize and excise dimers. DNA‑repair enzymes excise the damaged segment, and DNA polymerase fills the gap with the correct bases. While these mechanisms are highly efficient, overwhelming damage can overwhelm repair capacity, leading to mutations and cancer.
