Why RNA seperation only view 28S and 18S band in gel electrophoresis?

Question

I want to know details about human total RNA and ribosomal RNA subunit. What is total RNA? During RNA extraction, what the product that we get?

Answer 1

You get everything: rRNA, tRNA, mRNA, etc. mRNA is usually what you are interested it. You won't see the tRNA when you run it on a gel because they are small <100bp so they will be off the gel in a hurry. You see mosly ribosomal RNA (the 28 subunit and the 18) because this is the vast majority of the RNA that you have. If you are looking for a particular mRNA you will need to follow your extraction with a northern blot or RT-PCR.

Answer 2

When you isolate total cellular RNA you get all of the rRNA, mRNA and some of the smaller RNAs, such as tRNA, snRNA, etc. Most of the isolation procedures are limited in getting the true representation of the small RNA molecules, they tend to be biased against isolating small RNAs efficiently. When you run the RNA on a gel you see the bands for 18S and 28S rRNA because on a mole for mole basis, they are the most abundant, single discretely sized, transcripts produced in the cell. Most mRNAs are very much lower in abundance so they do not give a visible, discrete band when stained. There are some exceptions however. If you were to isolate RNA from reticulocytes, you would see the rRNAs and then you would also notice a smaller, but equally intense band. This would be the mRNA for globin. It is very abundant inside the reticulocyte. Another case would be from the chicken magnum oviduct, where you would see the rRNAs and then you would find a clear band for ovalbumin mRNA.

Answer 3

28s Rna

Answer 4

Your question is nonsense. Please give more details. Like did you do a reverse transcription reaction on the RNA first. What primer set did you use for the PCR etc. If you got a PCR product before DNAse treatment, but not afterwards then your RNA was contaminated with DNA and your PCR was probably just amplifying genomic DNA. Anyway please clarify what you did.