Why can’t the genetic code be taken directly from the DNA?
The genetic code is coding system through which information encoded in DNA or RNA sequences are translated into proteins.
The DNA or RNA sequence will determine which protein are to made and this specific protein made will determine specific activity. This how nucleus is define as the control center of the cell as genetic material DNA resides in the nucleus that control protein synthesis.
The genetic code cannot be taken directly from the DNA. As through central dogma of molecular biology information from genes flows into proteins: DNA → RNA → protein where RNA acts messenger that transfers DNA code.
DNA has very big and complicated structure that cannot leave the nucleus. Thus, mRNA acts as an intermediate between DNA and proteins. mRNA is like an informational molecule and tRNA acts as structure.
tRNA is required as DNA or RNA, cannot interact with amino acids directly.
Suppose if genetic code taken directly from the DNA then such a big sequence from DNA has to be cut and moved to the cytoplasm for protein translation and after that reattached the sequence in the same place in the DNA to code another protein which is not possible. Whole sequence of DNA is not used for protein synthesis thus, it is logical to convert only specific coding region of DNA into mRNA.