Is DNA altered before transcription takes place?

[fatima_a]

I though the mRNA was altered and stuff before the final protein product was made, but is DNA also altered because it's like a protection mechanism or something?

thanks

 

[Ygggdrasil]

DNA gets altered, but not in the same way that RNA gets altered.

In RNA, the actual sequence of the RNA can get modified (e.g. introns can get removed and a poly(A) tail gets added) and the 5' end of the RNA gets chemically modified by the addition of a cap.

The modifications to DNA that occur prior to transcription do not actually alter the chemical structure of the DNA but instead alter the proteins that package the DNA. In eukaryotes, DNA gets wrapped around proteins called histone proteins to form structures called nucleosomes. The wrapping of the DNA into nucleosomes is one reason why we can fit two meters of DNA into about an approximately six-micron-wide nucleus. However, for RNA polymerase to be able to begin transcribing the DNA, the DNA must be unwound from the nucleosomes. In this process, the histone proteins get chemically modified by enzymes called histone modifying enzymes. These chemical modifications act to help recruit other factors to that aid in transcription. Another class of enzymes, the ATP-dependent chromatin remodeling enzymes, also get recruited and help by removing the histone proteins from the promoter region, giving RNA polymerase access to the DNA.

 

[fatima_a]

wow thank you so much that was really very very helpful. i finally understand what my prof meant