Infectious Humor: A retrovirus carries genetic information in the form of RNA instead of DNA. A genetic throwback of sorts, since usual mechanism is DNA → RNA → protein. Retroviruses need an extra step: RNA → DNA → RNA → protein. According to the RNA World hypothesis, RNA is the earliest genetic material.
The virus type on the left is a bacteriophage. The one on the right is going through a hippie phage.
via Neural Stem World Community on FB. #scienceeveryday
madame scientist's not-so-mad musings 
this one always kills me!!!
mary Zeman , sticklers for accuracy complained that the one on the left was actually a bacteriophage, so I took care of that 😉
Hi rajini how are you
Nice post Rajini Rao 🙂
You’re welcome, good to see you smile Kershaw Rustomji 🙂
hii good evening Ranjini
mary Zeman “this one always kills me”… the one of the right might.
Ya! Actually the structure of retroviruses is a bit different!
But for the sake of art, it can be anything! 🙂
Just so that the poor bacteria do not feel left out, here is something that should make you smile Rajini Rao http://www.bbc.co.uk/news/health-18422288 🙂
And what exactly are the latest theories on how “replication” started?
Suhail Manzoor there are many experiments showing that RNAs can make copies of themselves. It has been proposed that some of those RNAs became the original replicators in the pre-biotic world. Of course, for natural selection to work, you need more than just a replicator. Some sort of membrane that separates the replicator and other useful RNAs from the environment and competitor RNAs is necessary. Natural selection will then favor those RNAs that are more efficient at copying themselves and other RNAs.
Suhail Manzoor , RNA is unique in that it can carry information, catalyze reactions and replicate itself. The study in this link demonstrated that RNA can copy itself: http://www.sciencedaily.com/releases/2009/01/090109173205.htm
So is the RNA replication more efficient than DNA replication then? Would it be fair to say that ultimately the optimising function here is one of energy here? Thanks for the responses Gustavo MacIntosh and Rajini Rao , wildly fascinating all this stuff 🙂
Suhail Manzoor The idea is that RNA is more reactive, and so can perform more functions. Thus, it was probably the original genetic material, and also carried enzymatic activity. DNA is less reactive, so it may have evolved later as a carrier of genetic information (less reactive, better chance to maintain genetic information stable). Even now, the building blocks for DNA are derived from the building blocks for RNA (which would suggest that RNA came first).
Suhail Manzoor , also, the replication of RNA in viruses is highly error prone as compared to DNA replication. This is so because of the lack of proof reading activity in RNA polymerases which is present in DNA polymerase enzyme which removes and corrects wrongly added base pairs in the newly synthesized strand of the DNA.
That is the reason that the rate of mutation in RNA viruses is so high! They simply keep changing due to the constant change which occurs in the base pairs of their genome itself.
So, in a way, DNA replication is comparatively more efficient.
Did I miss anything in that Rajini Rao ?
So Gustavo MacIntosh , could more complex organisms have evolved with just RNA then? From what you and Deeksha Tare are saying one of the fundamental differences between RNA and DNA is that the latter has superior error correcting design and I am guessing here, the DNA probably also has far more redundancy than RNA. I suppose this error correcting and redundancy comes at some energy cost that is probably higher in DNA than RNA. Does that make sense?
Yup! That’s true.
Suhail Manzoor , actually, from an evolutionary point of view, error correction would not be an issue. The polymerases that Deeksha Tare mentioned are proteins (that in the RNA world hypothesis evolved later), and the proofreading doesn’t have anything to do with whether they copy RNA or DNA (we can talk about proofreading later).
In terms of energy, RNA would be more convenient than DNA, since to make DNA you have to make RNA materials first. Thus, since evolution favored a DNA-based genetic code, energy is not the issue. Again, I think (and many other do too) that the main issue with RNA is that it has an extra chemical group that is lost in DNA. That extra group makes RNA much more reactive, and thus more prone to degradation. DNA, missing the extra group, is more stable. More stability in the genetic material ensures that the progeny will receive the same information that was present in the parent. In an stable environment this is an advantage.
Viruses have a high rate of mutation (i.e. are error prone), and this is also an evolutionary advantage because they are not in an stable environment -they are under attack by the immune system, and in a defense-counter defense evolutionary war with their hosts.
I think I’m rambling a bit, and I may not have answered your questions…
Thanks for fielding questions, Gustavo MacIntosh and Deeksha Tare while I’m traveling. Good stuff!
I imagine hippie phage is what Feisal Kamil looked like in college 🙂
Thank you Gustavo and Deeksha. Just one more question, do we know how DNA could have “lost” the hydroxyl group?
Suhail Manzoor remember, EVERYTHING is explained by evolution. Through evolution, those early cells acquiered enzymes capable of modifying the ribose of nucleotides to make dNTPs. Then, DNA was “born”. I can imagine that at some point there were hybrid polymers with NTPs and dNTPs. Later, specific polymerases and those proofreading activities we discussed earlier may have evolved, resulting in a better separation of DNA and RNA.
Suhail Manzoor you will probably enjoy this story. I’m linking to a blog talking about one of the DNA origin hypotheses, DNA invented by viruses.
http://scienceblog.com/10683/viruses-invented-dna/
This is a cool idea, although a few years old. The blog has links to 2 papers (from Nature and Science), hosted at a university, so you can access them for free.