Why does not use DNA as a template for translation, whereas RNA can directly use for encode protein?DNA was transcribed to mRNA first.  

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lynn30k eNotes educator| Certified Educator

It is a little difficult to understand your question as phrased, but I think you are asking why cells don't directly use DNA to encode for proteins, and instead go through the middle step of transcribing to mRNA first. One of the answers is that DNA, in eukaryotes, is an extremely long chain, encoding a lot of information. It is also enclosed in a membrane-bound organelle, the nucleus. As the proteins are formed OUTSIDE of the nucleus, it makes sense for a shorter chain, encoding only the info needed for that protein, to be transcribed, then go through the nuclear membrane to the cytoplasm. The building blocks for the proteins (amino acids), are in the cytoplasm.