Question

In changing from an “RNA world” to today’s “DNA world,” genetic information must have flowed from RNA to DNA. After reviewing Figures 17.4 and 19.9, suggest how this could have occurred. Does such a flow occur today?

Short answer

A flow of genetic information occurs from RNA to DNA with the help of the reverse transcriptase enzyme. In this type of flow, the RNA is used as a template to produce DNA. This reverse transcriptase enzyme could have played a significant role in changing from an ‘RNA world’ to today’s ‘DNA world.’

Today, the flow of genetic information occurs from DNA to RNA. However, the flow of genetic information from RNA to DNA happens today in viruses such as HIV.

Step-by-step solution

DNA and RNA

DNA and RNA are nucleic acids. They are the storehouse of genetic information.

DNA is the genetic material in almost all organisms, except a few viruses. Some viruses thus contain RNA as the genetic material instead of DNA. DNA is known to be more stable than RNA.

Explanation for part (a)

The transition from an ‘RNA’ world to today’s DNA world could have happened with the aid of the reverse transcriptase enzyme. It is an enzyme that catalyzes the synthesis of DNA from RNA. The enzyme acts on the RNA template to produce a single-stranded DNA complementary to the RNA strand.

This enzyme then synthesizes another DNA strand complementary to the first DNA strand formed. Thus, double stranded DNA is obtained. As the RNA serves as the template for DNA synthesis by the reverse transcriptase enzyme, the genetic information in the RNA is passed into the DNA.

Explanation for part (b)

Today, the DNA acts as a template for RNA or mRNA synthesis almost in all prokaryotic and eukaryotic cells. During this process, the genetic information from DNA passes into mRNA. The mRNA then undergoes translation for protein synthesis.

However, in some viruses, RNA is the genetic material. In such viruses, DNA synthesis from RNA occurs with the help of the reverse transcriptase enzyme. Here, the genetic information flows from RNA to DNA and not otherwise.

Therefore, today, the flow of genetic information mainly occurs from DNA to RNA. However, the flow of genetic information from RNA to DNA happens in viruses such as HIV, with RNA as the genetic material.