How to Store DNA

DNA is very sensitive and can easily degrade in certain conditions. Thus, proper storage is required to ensure high experimental standards. There are several mechanisms to store DNA for long periods of time.

DNA is often stored in liquid nitrogensruilk | Shutterstock

What causes DNA to degrade?

Chemical degradation is the main threat to DNA preservation. Potential nuclease contamination and the presence of free radicals can also cause damage to DNA and other nucleic acids, such as RNA. Storage strategies for DNA will depend on the type of DNA, temperature of storage, intended use of the sample, and the length of time that the DNA is to be stored for.

Storage in vitreous state

In vitreous state, molecules cannot diffuse, this means that a proton’s movement is limited to around one atomic diameter every 200 years, which effectively inhibits all chemical and nuclease degradation. Adding moisture to the dry state or raising the temperature will reestablish reactivity and movement of the protons, once more exposing DNA to potential damage.

DNA stored in a dry state will also remove water, which is active in hydrolytic reactions and can degrade DNA. Since moisture can reestablish proton movement, DNA stored in the dry state should be kept at low humidity.

Drying can be done by spray drying, spray freeze drying, and air drying or lyophilization. Of these, the latter is the cheapest and most popular method. Another method of dry long-term storage is on FTA cards, which enables preservation for 17 years. In general, DNA storage in dry conditions  optimum ibecause hydrolysis is the biggest cause of DNA degradation.

Medium length storage

Storage of the sample at -20 °C and -80 °C is less effective than storage in vitreous state, but can provides a useful short-term solution. Liquid nitrogen storage preserves DNA quality over the course of decades, whereas storage at -20 °C and -80 °C can prevent degradation for months or years.

To prevent degradation by chemical and enzymatic processes, DNA is often stored as a precipitate in ethanol, at -80 °C. This increases nucleic acids stability, but means that the ethanol must be removed prior to use. Hence, this technique is considered to be undesirable.

Repeatedly freezing and thawing DNA

A major misconception is that repeated freeze and thaw cycles have a deleterious effect on the quality of the DNA. However, studies show that repeated freeze and thaw cycles with up to 19 cycles have no detected DNA degradation.

Some studies indicate that DNA can be satisfactorily kept at room temperature and 4 °C. Such samples were kept in TE buffer, and were stable for 6 to 12 months. However, such DNA samples need to be monitored for DNA concentration and evaporation.

Further Reading

Last Updated: Apr 15, 2019

Sara Ryding

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Sara Ryding

Sara is a passionate life sciences writer who specializes in zoology and ornithology. She is currently completing a Ph.D. at Deakin University in Australia which focuses on how the beaks of birds change with global warming.

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Comments

  1. Jacques Bonnet Jacques Bonnet France says:

    this article gives a good account of the parameters determining the chemical stability of DNA. However it is incomplete and may give some false ideas.

    First, contrarily to what is said, freeze-thaw  does break DNA chain, but only the very long molecules (1). This may explain the contradictions

    Second, for room temperature storage in the dry state, in the absence of water, the situation is more complicated that it seems, because depurination and subsequent chain break still takes place (2).

    Third, what is said about the   procedures for long term DNA preservation is largely incomplete.
    Among other procedures there are matrices such as Biomatrica's (3) or Gentegra's (4). But as for FTA, the lack of protection from the atmosphere limits DNA's life time. Better is Grass' silica nanoparticles which completely mask DNA from air but still maintain some water (5). The best way has been shown to be DNAshells from Imagene company where DNA is kept under a neutral atmosphere maintained in a sealed stainless steel minicapsule. In these conditions, the DNA can be kept for thousands of years (2,6)

    1 - Shao, W., S. Khin, et al. (2012). "Characterization of Effect of Repeated Freeze and Thaw Cycles on Stability of Genomic DNA Using Pulsed Field Gel Electrophoresis." Biopreserv Biobank 10( 1): 4-11.
    2- Bonnet, J., M. Colotte, et al. (2010). "Chain and conformation stability of solid-state DNA: implications for room temperature storage." Nucleic Acids Res 38(5): 1531-46.
    3 - Howlett, S. E., H. S. Castillo, et al. (2014). "Evaluation of DNAstable for DNA storage at ambient temperature." Forensic Science International: Genetics 8(1): 170-178.
    4 - Kansagara, A. G., H. E. McMahon, et al. (2008). "Dry-state, room-temperature storage of DNA and RNA." Nat Meth 5(9): iv-v.
    5 - Grass, R. N., R. Heckel, et al. (2015). "Robust Chemical Preservation of Digital Information on DNA in Silica with Error-Correcting Codes." Angew Chem Int Ed Engl 54(8): 2552-2555.
    6 - Washetine, K., M. Kara-Borni, et al. (2018). "Ensuring the Safety and Security of Frozen Lung Cancer Tissue Collections through the Encapsulation of Dried DNA." Cancers .

    Jacques Bonnet , Emeritus professor, university of Bordeaux, scientific director of Imagene company.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News-Medical.Net.
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