As a biochemist with a focus on molecular biology, I can provide a detailed explanation on why DNA dissolves in water but not in ethanol. DNA, or deoxyribonucleic acid, is a molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses. It is composed of two polynucleotide chains that are coiled around each other to form a double helix, with backbones made of sugar and phosphate groups and four types of nucleotide bases attached to them.

The solubility of a substance in a solvent is determined by the interactions between the solute and the solvent. Water is a polar solvent, meaning it has a partial positive charge on one end and a partial negative charge on the other. This is due to the bent shape of the water molecule and the distribution of electrons within it. The polar nature of water allows it to form hydrogen bonds with other polar molecules, including the sugar and phosphate backbone of DNA. These hydrogen bonds are relatively strong and numerous, which facilitates the dissolution of DNA in water.

On the other hand, ethanol is a less polar solvent. It has a hydroxyl group (-OH) that is polar, but the rest of the molecule is non-polar. This makes ethanol less capable of forming strong hydrogen bonds with the DNA backbone. Moreover, ethanol is also capable of forming hydrogen bonds with itself, which can lead to the formation of a hydrophobic environment that is not conducive to the dissolution of DNA.

Furthermore, the solubility of DNA in a solvent is also influenced by the ionic strength of the solution. DNA carries a negative charge due to the phosphate groups in its backbone. In water, the presence of ions can shield these charges, reducing the electrostatic repulsion between the DNA strands and allowing them to interact more favorably with the water molecules. In contrast, ethanol does not have the same ionic strength and cannot provide the same level of charge shielding, which contributes to DNA's insolubility in ethanol.

Another factor to consider is the conformation of DNA. In water, DNA tends to adopt a more extended conformation, which increases its surface area and allows for more interactions with water molecules. In ethanol, however, DNA may collapse into a more compact form, reducing the surface area available for interaction and further decreasing its solubility.

In summary, the solubility of DNA in water compared to ethanol is influenced by the polar nature of water, the ability of water to form hydrogen bonds with DNA, the ionic strength of the solution, and the conformation of DNA in the presence of different solvents. These factors collectively contribute to DNA's preference for dissolving in water over ethanol.

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Because of these charges, polar molecules, like DNA or RNA, can interact electrostatically with the water molecules, allowing them to easily dissolve in water. Polar molecules can therefore be described as hydrophilic and non-polar molecules, which can't easily interact with water molecules, are hydrophobic.read more >>