The aim of this bachelor's thesis was to investigate non-canonical DNA structures, with particular emphasis on G-quadruplexes (G4), and their role in the human genome. The theoretical part provides an overview of their involvement in the regulation of gene expression, DNA replication, and the maintenance of genomic stability, as well as their potential as targets for the development of novel anticancer therapeutics. The experimental part investigated the effects of potassium (K⁺) and sodium (Na⁺) ions on the oligonucleotide aptamer AS1411, which adopts a G-quadruplex structure. Circular dichroism (CD) spectroscopy, UV-Vis spectrophotometry, and differential scanning calorimetry (NanoDSC) were used to evaluate its structural stability in the presence of these monovalent cations. The results showed that potassium ions markedly stabilize the G-quadruplex structure of AS1411, as demonstrated by a higher melting temperature compared with sodium ions. These findings confirm the significant influence of the ionic environment on the stability of G-quadruplex structures.
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