Can RNA turn into DNA and why or why not?

Answer 1

DNA stands for deoxyribo-nucleic acid. It is the extremely long molecule that contains the body's genetic code. When copying a gene to make a protein, a strand of ribo-nucleic acid is made - RNA. There are three types of RNA: Messenger, Tranfer and Ribosomal. in microbes (usually bacteria0, the genetic material isn't contained within a nucleus. You should research what a plasmid is to clarify your question.

Answer 2

Yes there is an enzyme called reverse transcriptase that makes a copy of the RNA in DNA. It is used by retroviruses such as HIV. These viruses are RNA viruses, but they code for reverse transcriptase as well as other proteins that are needed for by the virus.

The reverse transcriptase makes a DNA copy of the RNA genome of the virus using the RNA as a complementary template. Much like the normal process of DNA copying, but instead of using a DNA template using a RNA template and with a different enzyme to catalyse it.

The DNA copy then integrates into the host genome, permanently infecting the cell. When it is transcribed by normal DNA to RNA transcription the viral RNA is expressed and functions just as it would if the cell had been newly infected. This is one reason why HIV infections can lie dormant for so long.

Interestingly as well as viral reverse transcriptase there also appears to be reverse transcriptase that is endogenous, meaning it is present in an uninfected organism.

One theory is that all life was initially RNA based, but evolved reverse transcriptase from RNA to RNA copying enzymes because DNA is a more chemically stable than RNA and therefore is more useful molecule for the long term storage of information.

It is also theorised that reverse transcriptase is important because it enables evolution. It does this by gene copying. A normal DNA gene will be transcribed into RNA in the process of normal gene expression (which is DNA->RNA->Protein).

But if there is some reverse transcriptase hanging around then it is possible that the RNA can be turned back into DNA and then integrated back into the DNA genome at another spot. The genome now has two copies of the same gene.

Then each gene can evolve separately and specialise to handle slightly different situations, or even take on a completely different role with significant mutations, and all this while preserving the original gene, which was presumably useful for something or at least not harmful otherwise it would have been wiped out by natural selection long ago.

This explains how there are several instances of similar genes in an organism that do slightly different jobs, like alpha, beta and gamma haemoglobin. It also explains how the genomes of organisms dramatically increased in size over course of evolution.