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Well I'm well aware that it is proven that DNA contains genetic material via transformation and Hershey-Chase Experiment of T2 bacteriophage. Still I was wondering what is the reason only DNA contains it and not protein or RNA. What I've learned is that DNA is the most stable of all these molecules and it has the ability to replicate itself. Other than this I can't find any solid answere. Thanks!

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    $\begingroup$ RNA might contain material that you can classify as 'hereditary' (specific to that individual of the species, a subset of the species gene pool) but since the prevailing methods of meiotic gamete formation, sexual reproduction and the fact that all enzymes are formed due to transcription from DNA and not by the inherited RNA, DNA is the one that is inherited and hence acts as the heredity carrier and not RNA. $\endgroup$ – Satwik Pasani Sep 1 '13 at 10:39
  • $\begingroup$ DNA/RNA also has a relatively obvious way by which it can be replicated- having a purine base pair with a pyrimidine. $\endgroup$ – biogirl Sep 1 '13 at 15:12
  • $\begingroup$ RNA has the ability to replicate itself - it could be the genetic material, but it simply isn't. its degraded in the cell quickly. its hard to be hereditary material when you are destroyed. $\endgroup$ – shigeta Sep 1 '13 at 17:40
  • $\begingroup$ @shigeta, certainly there are RNA viruses that are excellent examples of RNA functioning as hereditary materials. $\endgroup$ – bobthejoe Sep 6 '13 at 10:05
  • $\begingroup$ that's true, but trying to respond to the question as stated as i see it, not sure its what i wanted to point out. $\endgroup$ – shigeta Sep 6 '13 at 18:13
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I think any discussion of this question can benefit from a historical perspective. For a long time, it was in fact believed that proteins was the hereditary material. The Nature Scitable page on the discovery of DNA (1) starts with the following passage:

In the first half of the twentieth century, Gregor Mendel's principles of genetic inheritance became widely accepted, but the chemical nature of the hereditary material remained unknown. Scientists did know that genes were located on chromosomes and that chromosomes consisted of DNA and proteins. At the time, however, proteins seemed to be a better choice for the genetic material, because chemical analyses had shown that proteins are more varied than DNA in their chemical composition, as well as in their physical properties.

While perhaps easy to dismiss in hindsight, it is possible to understand the reasoning of the day. The "central dogma" of molecular biology, that genetic information flows from DNA to RNA to proteins was only described later, and explained how the production of complex proteins consisting of 20-odd amino acids can be directed by a polymer consisting of only four nucleotides. This allows great complexity and variety in phenotypes while maintaining simplicity of the genetic material. The central dogma also facilitates the seperation of the use (through protein expression) and storage (as DNA) of genetic material.

As Watson and Crick noted in their famous paper, the double helix of DNA, when discovered, immediately suggested how the genetic material could be elegantly copied. While the more complex structure of proteins would likely require a more complex copying mechanism, the specification of amino acids through three-nucleotide codons in DNA allows the regularity of the DNA material to be retained for easy replication while allowing complex proteins to be produced.

However, even though DNA is the primary genetic material today, the situation may have been different at the time life first appeared. According to the RNA world hypothesis, RNA may have been the original genetic material and that DNA is a variation of RNA, not the other way around as it is commonly seen.

For a fuller historical perspective, I recommend the book "What is Life?" by Erwin Schrödinger, which was written before the discovery of DNA as the genetic material.

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In contrast to some of the accepted points in this thread. DNA is not the only hereditary material. The RNA world hypothesis remains hypothetical, but its primary point is that RNA may have been the original hereditary material as it is slightly simpler than DNA. However, there are extant organisms that use RNA as their genomic basis.

There are many viruses which use RNA based genomes (either single stranded or double stranded, (Class IV/V and Class III viruses as described by the Baltimore Classification). There are also class VI viruses which use an RNA genome that passed through a 'DNA intermediate' phase during the infection/replication process. The latter class are "Retroviruses" as they need their genomes to be converted back to DNA. The most famous example of such is the HIV virus.

Crucially, the progeny viral particles re-package RNA, which is carried with them until the next infection cycle, making it their hereditary material.

(I realise this is an old thread at the time of my answer, but this is important for completeness)

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    $\begingroup$ Further, piRNAs can serve as hereditary material in animals: e.g.: Houwing, S., et al., A Role for Piwi and piRNAs in Germ Cell Maintenance and Transposon Silencing in Zebrafish. Cell, 2007 $\endgroup$ – tsttst Jan 13 at 1:52
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The simplest answer one could offer to this question is hidden in the structure of the DNA itself. DNA is double helix structure with the presence of 3'->5' end and 5'-3' coiled helically in the double strand ( it is the direction in which DNA is synthesised as per formation of replication fork via the enzyme DNA dependent DNA polymerase. Replication fork (source google search)

The inability of the Proteins, amino acids etc to replicate themselves makes no sense to have them as genetic material ( as also concluded by Martha and chase experiment). Now, here is the point which leads the most logical question? Why not RNA ? In fact it is much better in the Job that DNA does, it is very fast in replication almost have the same structure, but the fact that the presence of OH group makes RNA very reactive and Unstable does not make it idle for transfer of hereditary material in nature, we should know that thousands of nucleotides are synthesized by DNA polymerase during the replication of DNA from the template DNA which is highly accurate and precise even slightest of error can lead to very big mutation and the presence of the Deoxyribose and complementarity principle makes the DNA best suited for Genetic material.

Although a whole of a different class of the organism exists that have RNA as genetic material, they are called retroviruses eg. HIV virus so the question that DNA is the only genetic material in all living organism is not true, although yes it is the genetic material in Humans and majority of the organism due to the above reasons.

EDIT : AS @WYSIWYG mentioned there are also many viruses which have RNA as genetic material but are not called Retroviruses, nonetheless DNA is not the only genetic material that exists.

Kapeesh !

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  • $\begingroup$ Viruses with RNA as genetic material are simply called RNA viruses. There are many RNA viruses that are not retroviruses (for e.g. poliovirus, influenza virus). $\endgroup$ – WYSIWYG Jan 11 at 11:16
  • $\begingroup$ @WYSIWYG something interesting you made me learn today. Thank you so much. $\endgroup$ – Dumbty Jan 11 at 15:24

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