Biomolecular condensates are a type of membrane-less organelles formed by liquid-liquid phase separation, containing mainly proteins and nucleic acids. In condensates, a chemically different environment is created by the selective inclusion of some macromolecules and the exclusion of others. Condensates can perform a number of roles in the cell: separating cellular contents by transporting and localising nucleic acids, creating a favourable environment for catalytic processes, storing selected molecules, and responding to stress. Mutations in key components or deregulation of condensate formation lead to pathological conditions such as neurodegenerative diseases and myopathies, for example ALS, Huntington's disease, Alzheimer's disease and frontotemporal dementia. The role of proteins in the development of these diseases has been intensively explored, but less is known about the contribution of RNA, even though RNA is thought to provide a scaffold for protein binding, and RNA–RNA interactions directly trigger the initiation of liquid-liquid phase separation. This calls for a more detailed exploration of the RNA properties required for the formation of the different biomolecular condensates and an understanding of the dependence of the system on a range of chemical factors. As a part of the MSc thesis, we selected eight different RNA sequences with expansion repeats (G$_4$C$_2$, CAG, CUG, CCUG, CGG, AUUCU, UGGAA and GGCCUG) occurring in neurodegenerative diseases and myopathies to observe the influence of the RNA properties (sequence, length, formation of higher order structures) and the environment (concentration of potassium and magnesium ions, concentration of the RNA, pH, addition of polyethylene glycol) on the process of separation of the liquid phases by UV spectroscopy. By measuring turbidity we observed that the length of repeats in the sequence does not affect the phase separation process. However, the effect of the number of iterations on the increased turbulence is noticeable. The presence of potassium ions causes increased turbidities for the (UGGAA)$_n$ and (CGG)$_n$ sequences, where potassium ions also stabilise the predicted higher-order structures. Magnesium ions cause increased turbidity, especially for the (G$_4$C$_2$)$_n$ and (GGCCUG)$_n$ sequences. High RNA concentration has a positive effect on turbidity for (UGGAA)$_n$, (G$_4$C$_2$)$_n$, (CGG)$_n$, (GGCCUG)$_n$ and (CAG)$_n$, while the addition of polyethylene glycol results in an increased turbidity for (G$_4$C$_2$)$_n$, (CGG)$_n$ and (GGCCUG)$_n$.
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