Here's why:
* RNA precipitation: Ethanol helps to precipitate RNA from solution. RNA is very soluble in water, but when ethanol is added, it reduces the solubility of RNA, causing it to come out of solution as a solid precipitate.
* Washing away impurities: During the washing step, ethanol helps remove contaminants such as salts, proteins, and other cellular debris that may be present in the RNA sample.
How it works:
1. Dehydration: Ethanol is a dehydrating agent, meaning it removes water from the solution. This reduction in water content lowers the solubility of RNA, leading to precipitation.
2. Salt effect: In most RNA extraction protocols, a salt solution like sodium acetate is added before ethanol. This salt helps to neutralize the negative charge of the RNA molecule, making it less soluble in water and more likely to precipitate.
3. Selectivity: While ethanol precipitates RNA, it doesn't precipitate DNA as efficiently. This helps to ensure that the final RNA sample is relatively free of DNA contamination.
Important considerations:
* Ethanol concentration: The concentration of ethanol used in RNA extraction is crucial. Too low of a concentration may not be effective in precipitating RNA, while too high of a concentration can lead to the precipitation of other unwanted components. 75% ethanol is commonly used because it provides an optimal balance for precipitation and washing.
* Temperature: Ethanol precipitation is typically performed at low temperatures, often on ice or at 4°C, to minimize degradation of RNA.
Overall, 75% ethanol plays a critical role in RNA extraction by precipitating RNA from solution and washing away contaminants, ensuring the isolation of pure and intact RNA.
