A technologist in a tissue bank who performed HLA typing by DNA analysis was asked to bank all DNA extracted from specimens received in the laboratory so as to maintain the highest quality of nucleic acid for the longest period. How should the DNA be stored to satisfy this request?

I believe the options are:

a) DNase-free water at 22°-25°C

b) DNase-free water at - 70°C

c) TE buffer at 2°-8°C

d) Freeze-dried at 22°-25°C

The answer is d) freeze dried at 22°C to 25°C.

Explanation:

As compared to RNA, DNA is a relatively stable biomolecule. It is relatively thermostable. However, DNA is highly susceptible to nuclease and chemical degradation.

DNA Storage:

DNA storage methods depend upon the type of sample, the desired quality and for how long the sample needs to be stored. There are four major DNA storage methods: Dried, at room temperature - 20°C - 80°C - 196°C (storage in liquid nitrogen) Freeze drying and storage in liquid nitrogen (-196°C) are the two most effective means to store DNA samples for a long time. For storage at room temperature, DNA samples are dried in a freeze drying machine. Freeze drying removes all the moisture and water from the sample which prevents any hydrolytic reactions.