thymine dimer

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thy·mine di·mer

a product of ultraviolet irradiation of thymine (free in ice or bound in nucleic acids) in which two thymine residues become linked by formation of a cyclobutane ring involving both C-5's and both C-6's at the expense of the two double bonds; several stereoisomeric forms are possible.

Farlex Partner Medical Dictionary © Farlex 2012

thymine dimer

a pair of adjacent THYMINE residues in a single POLYNUCLEOTIDE CHAIN that have become chemically bonded, usually by the action of ULTRAVIOLET LIGHT. The lesion can inhibit DNA replication unless repaired. However, the processes responsible for repairing the lesion sometimes make errors, in turn creating MUTATIONS. see XERODERMA PIGMENTOSUM.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

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"The topical combination was particularly effective for reducing thymine dimer mutations which are associated with skin cancer," explained Jacknin.

The Sun Shines on Cosmetic Chemists: Although a devastating hurricane hit the region, the biannual Sunscreen Symposium sponsored by the Florida Chapter of the SCC went on as scheduled

The formation of the stable excimer along the lowest singlet excited-state for stacked cytosine molecules may make the formation of cyclobutane cytosine dimer (C<>]C) less efficient compared to the formation of cyclobutane thymine dimer (T<>T) from a stacked pair of thymine molecules, which do not form a stable excimer.

Competing deactivation channels for excited [pi]-stacked cytosines

However, thymine dimer repair was markedly reduced in mice lacking the VDR, indicating that these mice have defective DNA repair mechanisms in UV-induced damage.

Inactivation of the vitamin D receptor enhances susceptibility of murine skin to UV-induced tumorigenesis

Compared with placebo, treated individuals with low baseline MED had a 50% reduction in epidermal sunburned (apoptotic) cells and nearly a 60% reduction in DNA damage, as measured by thymine dimer formation.

Synthetic melanin tans skin, reduces cellular UV damage

Compared with placebo, individuals with low baseline MED who were administered the hormone demonstrated a 50% reduction in epidermal sunburned (apoptotic) cells and nearly a 60% reduction in DNA damage, as measured by thymine dimer formation.

Hormone tans fair skin, screens sun

This failure ultimately leads to permanent damage to the DNA--a gene mutation known as a thymine dimer. Thymine dimers are caused only by UV light.

Looking at SKIN CANCER in a Different Light

Barton has found that electron transfer can fix a mutation known as a thymine dimer, in which two thymines on the same DNA strand bond together.

An Electrifying DNA Debate

(1) In a small 2008 study, a stable formulation of 15% L-ascorbic acid, 1% alpha-tocopherol, and 0.5% ferulic acid was applied topically to normal-appearing human skin for 4 days and was found to impart significant photoprotection against solar-simulated UV radiation and was especially effective at diminishing thymine dimer mutations, which are linked to skin cancer.

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(23-24) Further, ferulic acid has been shown to stabilize both vitamins, with the topical combination yielding photoprotective effects against UVB exposure, including the significant reduction in thymine dimer formation.

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Upon irradiation with ultraviolet (UV) light, two adjacent structures--thymines--along a strand of DNA may fuse into a thymine dimer. These dimers present roadblocks to normal DNA synthesis and are likely to spawn mutations if they are not repaired before the cell's DNA undergoes replication.

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They found that the antioxidant formulation supplemented the antioxidant pool of the skin and conferred significant photoprotection, guarding the skin against erythema and apoptosis as well as effectively suppressing p53 activation and reducing thymine dimer mutations known to be associated with skin cancer.

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DNA damage results when UV light induces covalent bonds between nucleic acid base pairs and forms thymine dimers, which can alter tumor suppressor gene p53 function, thereby increasing the risk of cutaneous cancers and aging.