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In lab. ethanol always used child while isopropanol is at room temperature. what is the reason behind this?

for DNA isolation we have use child ethanol which can be replaced by isopropanol but I could not understand that why ethanol could not use at room temperature and isopropanol could not use child.

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  • Stephanie Cadot · University of Sussex
    If you mean to precipitate DNA, then from my own experience when precipitating DNA with cold isopropanol (-20C) you may get precipitation of lots of salt (white precipitate at the bottom of the tube). It took me a week of rinsing everyday my sample with -70C ethanol afterward to get rid of all the precipitated salt and get a DNA sample that can be used in further experiments. So it could be a reason.
  • Muhammad Yasar · Advanced Neuroscience Allies Pvt. Ltd
    Dear Bhumi,

    Using ice-cold ethanol and ice-cold water increases the yield of DNA. Low temperatures protect the DNA by slowing down the activity of enzymes that could break it apart. A cell’s DNA is usually protected from such enzymes (DNases) by the nuclear membrane which is disrupted by adding detergent. DNases in the cytoplasm would destroy the DNA of viruses entering the cell. Cold ethanol helps the DNA to precipitate more quickly. (Ref: http://www.practicalbiology.org/areas/introductory/bio-molecules/dna/extracting-dna-from-living-things,83,EXP.html)

    also

    The colder the ethanol, the less soluble the DNA is.
    (Ref: http://www.occc.edu/bbdiscovery/documents/modules/dna%20extraction%20lab.htm)

    other related answers:

    1. Having ice cold ethanol only increases the rate of precipitation of DNA and helps increase yield of DNA. You can either use room temp or ice cold ethanol for DNA precipitation. You can think about precipitation of a super concentrated solution as you decrease the temp. As the temp decreases, the amount of precipitation increases. Overall temperature affects solubility. As temperature decreases the substance becomes more insoluble (in general. this doe snot apply to every molecule). SO ice cold EtOH allows for more DNA to interact together and allow for a more rapid and efficient precipitation of DNA. (Ref: http://in.answers.yahoo.com/question/index?qid=20110704135752AAq48Li)
  • Stephanie Cadot · University of Sussex
    I forgot to say that what happened with the isopropanol doesn't with ethanol that's why you can and commonly use it cold to increase your yield of DNA indeed!
  • Sudeshna Patnaik · Osmania Medical College
    Low temperatures protect the DNA
  • Brahmaraju Mopidevi · University of Toledo
    Water is a polar molecule and it has a partial negative charge near the oxygen atom due the unshared pairs of electrons, and partial positive charges near the hydrogen atoms. Nucleic acids are hydrophilic due to the negatively charged phosphate (PO3-) groups along the sugar phosphate backbone therefore nucleic acids can interact electro statically with the water molecules, allowing them to easily dissolve in water.

    When we use ethanol in the presence of sodium acetate, sodium acetate breaks up into Na+ and [CH3COO]-. The positively charged sodium ions neutralize the negative charge on the PO3- groups on the nucleic acids, making the molecule far less hydrophilic and therefore much less soluble in water causing nucleic acids to drop out of solution. This charge neutralization will be more in the presence of chilled ethanol and also lower temperatures promote the flocculation of the nucleic acids so they form a larger complex that readily pellets under the centrifugal forces of a micro centrifuge.

    The main difference between isopropanol and ethanol is the solubility of DNA in each solvent. DNA is very less soluble in isopropanol so it will fall out of solution much faster at a lower concentration and low volume. The convenience of using isopropanol is no need to use salts and can be done at room temperature and also takes less time to precipitate nucleic acids. Approximately DNA falls out of solution in 35% isopropanol where as when we use ethanol the final concentration needs to be around 75%. So we need to use more volume of the chilled ethanol to precipitate the nucleic acids.
  • Noel Derecki · University of Virginia
    Simple: martinis taste best chilled! :)

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