What is the purpose of ethanol in a DNA extraction experiment? We were doing a lab experiment in biology class in which we extracted DNA from a banana-detergent solution mixture.(The detergent solution was made of 100ml of detergent, 90ml of water, and 5g of salt.) We then added ethanol to the mixture. I know detergent breaks down the lipids in cells and salt takes away the moisture from cells but how does ethanol affect cells?

In the case you describe the ethanol is not there to do anything with the cells but to make the DNA precipitate out of solution. DNA is very poorly soluble in 50-70% ethanol and it will precipitate out as a white sticky pellet. It works even better if the alcohol is kept very cold.

Ethanol does kill cells by denaturing proteins and disturbing the lipid bilayers but after you have added the soap, most cells will already have been disrupted.