[–] dangerous_ai 2 points 11 points (+13|-2) ago 

The answer to your questions begins with ribozymes, which are catalytic RNA molecules. One important difference between RNA and DNA is the presence of a hydroxyl ( -O-H ) group at the 2' position on the ribose ring on RNA (ribo(se) nucleic acid). That hydroxyl group is absent in DNA (de-oxy(gen) ribo(se) nucleic acid). This additional hydroxyl group can perform catalytic chemistry. There are ribozymes that can replicate themselves, and it's thought that these were the bootstrapping molecules which ultimately lead to ribosomes.

This is called the RNA world hypothesis, where a soup of RNAs, DNAs and amino acids ultimately started organizing first with catalytic RNAs.

Ribozymes that can replicate themselves can lead to larger ribozymes that can replicate. Different self-replicating ribozymes that have other catalytic functions. Perhaps one ribozyme is particularly good at the organic chemistry needed to assemble 2 specific amino acids in order. A small amino acid chain (5-7 amino acids long) could provide a stabilizing framework for multiple ribozymes, and now there's a larger molecule that can perform multiple chemistries.

All of these "what-ifs" have been shown in to exist in biochemistry labs. We're talking about geological time scales, though, and once a replicating unit is formed the evolutionary race has started. If some chemical modification occurs that makes one replicating unit more efficient, it will out compete the rest.

[–] Hydrocephalus [S] 1 points 4 points (+5|-1) ago 

Ok, that sounds good. I'll look into this RNA world hypothesis some more.

[–] littul_kitton 0 points 9 points (+9|-0) ago  (edited ago)

Ribosome evolution is a major mystery. Their scaffold is RNA, which is rare in cells. But they also require numerous proteins. One theory is that the ribosome is a living fossil, a relic of a primitive like form based on RNA.

Read up on viroids. These are loops of RNA that replicate without conventional chromosome methods. They cause several important plant diseases. Some recent questionable research even implicates then in human prion disease.

If you really want to blow your mind, study introns. These are genetic segments that are chopped out before making mRNA.

Chopped out by what? The spliceosome! It takes the raw mRNAs and edits them to produce the final mRNAs that turns into proteins. The spliceosome is very complicated and there is no obvious reason for it to have evolved.

Also check out vault particles. They are virus-like protein capsules. They have vRNAs - short RNA segments - that are part of their structure and may help route them to their destination.

[–] Hydrocephalus [S] 0 points 5 points (+5|-0) ago 

Thanks! With the exception of introns, I haven't heard of these things yet. Considering weird genetic stuff, have you heard of retroviral like elements? These are sections of DNA that can pop out and reinsert themselves at other locations, it is hypothesized that they are ancient retroviruses living in our genetic code and that they help drive generic variability.

[–] kingminos 0 points 1 points (+1|-0) ago 

Great short discussion. I did not know INTRONS needed to be hacked. My long-ago BioPhys prof taught that rybozymes were a huge scramble, but "god" is spelled T-rna !!

[–] feral-toes 0 points 7 points (+7|-0) ago 

I think it is very hard to imagine a pre-biotic world. Now-a-days life is everywhere. Put out food and it rots. But even inhospitable surfaces host life. Look at moss growing on rocks. The world we live in is aggressively post-biotic. It is not just that there is life, but life is ravenous and eats everything. Either there are fancy bacteria fighting each other with chemical weapons such as penicillin or they are eating each other or dying due to infection by bacteriophages, or the surface has been briefly sterilized by severe measures.

But before life, there is no eating. All sorts of nutritious chemicals, if they form through abiotic processes, just lie around, waiting, waiting,... Maybe accumulating in ways that are completely counter-intuitive. We are talking about a planet sized, gooey organic mess, just sitting there.

[–] patriot_biz 0 points 0 points (+0|-0) ago 

This is deep. I think that the other thing to consider, and here I'm bumping into the limit of what I understand about geology, is that the Earth was very different back then.

[–] PhimoticEmbrace 0 points 4 points (+4|-0) ago 

Thrombolites and Stromatolites are worth reading about if you're curious about microbial mats and energy retention/absorption. The Earth was still cooking back then, so there were interesting ways that organisms survived. I think volcanoes and toxic vents were a key factor.

[–] patriot_biz 0 points 3 points (+3|-0) ago 

I am not a biologist. Why not suppose that transcription and translation beat out earlier, less efficient processes that died off and were replaced. Expensive? Perhaps but maybe very efficient. Absent these 'expensive' process you don't get heredity. Perhaps these processes are so efficient that, even if they took millions of years to evolve from primordial/self-replicating polymers, they gave rise to a multitude of categories of life.

Compare against prions. Prions are pretty cool but aren't as adaptable as DNA/RNA based critters. Virus are also interesting but overall fragile.

DNA/RNA has the advantages of being self-replicating, and modifiable. As a process, any activity that has both of those qualities qualities may spread rapidly.

Don't overlook the possibility that DNA/RNA arose on another planet and hitch-hiked on a comet or something. In the primitive Earth, they'd have found a ripe opportunity to leak out into our primordial oceans and create life.

[–] mirimar 0 points 2 points (+2|-0) ago 

The alien argument just puts the whole question off. How then did the molecules form on those planets/ comets? They had to start somewhere.

[–] Hydrocephalus [S] 0 points 2 points (+2|-0) ago 

The way I've seen it play out in science fiction is that the reason we don't see a wide variety of microbes with unusual DNA systems or protein synthesis is that life started on another planet and we just wound up getting seeded with some DNA using bacteria. Probably not how it worked out but slightly plausible.

[–] patriot_biz 0 points 0 points (+0|-0) ago 

But that wasn't what I was talking about. The question was 'what's the origin of transcription or translation', not 'what's the ultimate origin of RNA?'

Your implied question is disingenuous.

[–] Hydrocephalus [S] 0 points 1 points (+1|-0) ago 

I was asking if anyone knew of these earlier less efficient processes. Check out some of the other answers if you haven't yet, some of them have some interesting things to look up and read about.

[–] Dortex1 0 points 3 points (+3|-0) ago 

[–] Mjazz 1 points 1 points (+2|-1) ago 

They say bats evolved from rodents. Try selectively breeding some kind of rodent so that it's fingers get longer with webs between them. Probably never happen, but if you succeed, try and get it to fly. What would be the advantage of long fingers with webs anyway? Why would they get longer and longer with bigger and bigger webs? If we can't do it with selective breeding how did nature do it? Evolution is a scam.

[–] thebearfromstartrack 0 points 1 points (+1|-0) ago 

How come we NEVER hear about RNA any more?

[–] Hydrocephalus [S] 0 points 1 points (+1|-0) ago 

I hear about RNA all the time, there is a new drug coming out that is an interfering RNA, it binds with messenger RNA and degrades it which causes a protein to not be translated. It's called a PSK9 inhibitor and it lowers cholesterol better than statins and appears to not have serious side effects. It blocks the creation of a protein that degrades a protein that pulls cholesterol out of the blood, sort of a double negative situation.

[–] thebearfromstartrack 0 points 0 points (+0|-0) ago 

So is RNA a double helix too? With a code? Is it side by side with DNA? How come they don't catch criminals with RNA?

[–] prairie 1 points 1 points (+2|-1) ago 

Ever cracked open a biology textbook?

[–] thebearfromstartrack 1 points 0 points (+1|-1) ago  (edited ago)

Once, but it was boring. I am a MATH guy, Biology is ooky, and stinky.

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