Evolution

[Guest akscience]

Hopefully someone knows more about this than I. But amino acids are made up of DNA and DNA are made up of amino acids, correct. Obviously this is a pretty vage statement, yet holds some truth correct. My question would be, how can you have one without the other to create the first living protein (not to mention how to you get life from non-life). Someone once said it's like the chicken or the egg concept, well that doesnt fly, theres gotta be a way DNA makes amino acids or visa vera. Anyone have any thoughts on this.

 

Kevin

[Radical Edward]

amino acids are not made of DNA, they are constructed by enzymes and so on though, though they also exist in abundance throughout the universe and can and have been created spontaneously given the correct conditions and chemical mix (i.e. the conditions and chemical mix on earth a few billion years ago for example.)

 

ah, and what you are talking about isn't evolution, it is abiogenesis. though some others here like sayonara might know more than me about these things.

[Skye]

Just a few points...

*DNA (DeoxyreiboNucleic Acid) is made of nucleic acids

*Amino acids are made of an amine, a carboxylic acid and a variable funtional group

*Proteins are made of amino acids

[Guest akscience]

Enzymes are Proteins: All enzymes are made of protein.They consist of long chains of amino acids, hold together by peptide bonds.They increase the rate of chemical reactions without being consumed in tehe process. Enzymes are biological catalysts: Enzymes are specialized proteins which are able to conduct chemical reactions under biological conditions.

 

Enzymes are Specific: Most enzymes have very specific functions, and convert specific substrates to the corresponding products. Since amino acids are chiral, enzymes also show chirality, and will often act on only one enantiomer of a given substrate. The catalytic site has been optimized to perform a specific reaction, in order to accept substrate selectively and to transform the substrate into the product in a regio- and stereoselective way. How can you have one without the other?

[Skye]

DeoxyriboNucleic Acid

[Radical Edward]

Originally posted by Skye

Just a few points...

*DNA (DeoxyreiboNucleic Acid) is made of nucleic acids

*Amino acids are made of an amine, a carboxylic acid and a variable funtional group

*Proteins are made of amino acids

 

yeap, sorry, you can tell I don't study this...

[Radical Edward]

Originally posted by akscience

How can you have one without the other?

 

you don't need to have both... just because enzymes are this good now doesn't mean they always have been this good, early enzymes were probably just relatively inaccurate things that stuck a load of chemicals together, in fact I have heard of a suggestion that really early enzymes could have been made from RNA rather than amino acids, though I haven't looked into it much.

[Sayonara]

By heading this thread "Evolution" you answered your own question.

 

It is the same answer as the chicken and egg problem.

[Guest akscience]

"By heading this thread "Evolution" you answered your own question.

 

It is the same answer as the chicken and egg problem."

 

Say, i would fail to believe that science would agrue this problem as "the chicken or the egg". This is the biggest cop out answer of all time

[JaKiri]

The answer is the egg by evolutionary theory btw, and I believe that's what he's referring to.

[Sayonara]

I said the answer was the same as the answer to the chicken and the egg problem, because by definition the two questions are the same.

 

Hence, the answer is the very title you selected - evolution.

 

As to the actual mechanisms of development of a self-supporting amino acid // DNA 'production line', you'd have to ask a molecular biochemist I'm afraid (don't really go into that in depth even in degree level biology )

[Guest sage]

read LIFE WITHOUT GENES by Adrian Woolfson. has tons of information but is a little boring.

[Giles]

Briefly, there are many theories, but the leading two are essentially the 'RNA world' and the 'reductive membrane', or a combination of the two. I'll simplify since i'm guessing you don't know a lot of biochemistry. Please bear with me here.

 

RNA is a carrier of genes, in structure very much like DNA. It is more primitive, and is no longer used by much life on earth to store genes. DNA is less reactive than RNA. This has two consequences:

 

- DNA makes a better storage material for genomes, because it is less prone to be damaged.

 

- RNA displays some catalytic activity - like enzymes, it is able to affect reactions, and so act as cell machinery. Such RNA, called 'ribozymes', performs some functions in the cell.

 

Since RNA is involved in making proteins from DNA as both an intermediate messenger carrying the genes to the protein 'factory', and as part of that factory (a ribosome), it is thought that originally almost all organisms used RNA for both their genome and some metabolism.

 

Now, RNA's ability to act as an enzyme is determined directly by its sequence, just as a protein's activity is determined by its sequence. This immediately suggests an origin for genes - a fragment of RNA could be both a gene and the ribozyme it coded for.

 

Under certain conditions, which probably existed on ancient earth, nucleotides could spontaneously form, and link into polymers of RNA. These would have some limited catalytic effect. If any RNA chain should happen to catalyse its own formation (and such 'autocatalytic' chains do exist in both nature and experiment), then it would be possible for evolution to begin. The RNA would copy itself, and some of the copies would be erroneous. Some of these would be better at copying themselves, and so after a while there would be more of them.

 

The problem with this is something called the 'eigen paradox'. Short genomes can't code for the ability to accurately copy long genomes, and inaccurate copies tend to be worse at their job. so after a while genomes can't realistically get longer, and this would be far before anything as complex as modern organisms arose.

 

The solution may lie partly in the 'reducing membrane', which would be a sheet of something like iron (III) sulphide. The RNAs would be confined to this surface (instead of free to float around in three dimensions as i've described above), making reactions more favourable and also increasing the chance of a molecule being surrounded by its immediate neighbours. Even better, the iron surface would promote the formation of something like a genuine cell membrane. Once this sort of thing starts to happen, lots of short RNAs can get together and confer benefits on one another.

 

Without getting into the technicalities of modes of evolution and selection, this effectively allows the eigen limit to be bypassed, as multiple RNAs within a membrane can act together to increase the chances of them all multiplying. furthermore, such membranes would tend to divide into two spontaneously as their volume increased (they would take on more reactants and water due to osmosis and diffusion). This would be the beginning of cell division. Seperate cells could then undergo selection, and you're off! \o/

 

I'd recommend the first few parts of "The Major Transitions in Evolution" for more detail, but it is quite technical.

 

I'll try to answer any questions. If any of that needs more explanation just ask. i've probably got some things wrong too, for which i apolgise, and which i hope sayonara or ed will spot.

[Chaos Theory]

HIV is two strands of RNA. Is 2 strands more 'evolved' for a virus? Then we can get into reverse transcriptase-an enzyme that is used to convert the RNA to DNA so it can enter a cell's DNA...

[Giles]

"more evolved" is a very vague term, but i'll tackle a few perspectives:

 

- The idea of some organisms being "more evolved" or "higher" than others is really nonsense. No organism can be more evolved than any other, since they are all held to have an equally long evolutionary history. Nevertheless, the term 'higher organism' is used by biologists to describe either eukaryotic organisms (those whose cells have internal membranes) or true multicellular organisms.

 

- The use of DNA is a more advanced (in limited temporal terms) adaptation than RNA in the sense that it appeared later in evolutionary history.

 

- However, just because DNA is double-stranded does not mean that double-stranded RNA is 'more advanced' than single-stranded, except in the limited temporal sense mentioned already. DNA is usually double-stranded because of the mechanism of replication used, and so that it remains inert when not in use (at which point the helix is temporarily unwound to reveal the seperate strands).

 

- Double-stranded RNA is found in HIV because of the way it works. Most viruses want to get into a cell, and immediately start reproduction, for which single-stranded RNA is useful because it is what is used to make proteins.

 

- It is possible that the genetic material used by viruses is actually a simplification of more 'modern' systems, as viruses may have evolved from cell components (such as bacterial plasmids) which "went rogue". Viruses are parasites, and parasites tend to cast off anything not directly related to reproduction if they can get it from the host instead. note also that the size and nature of the genome is likely to be limiting to the generation time of the virus, whereas other factors are more important in 'higher' organisms.

 

i can go into more detail if you want. biologists tend to use language in sloppy way when describing evolution, which can be misleading. it is best just to think in terms of adaptations being gained and lost.

[Chaos Theory]

Good advices there.

 

Double-stranded RNA is found in HIV because of the way it works. Most viruses want to get into a cell, and immediately start reproduction, for which single-stranded RNA is useful because it is what is used to make proteins.

 

Dang, gotta hit the microbiology text again here. I was thinking single stranded rna viruses coded for DNA that would go into the cell's DNA in order to take over the cell. It's been 10 years though...little fuzzy. Then the necessity of reverse transcriptase for the HIV is not making sense there...ack!

[Giles]

Depending on conditions, sometimes it pays a virus to use the host to produce more virus particels, and sometimes it pays to just sit in the host genome and be replicated along with it. the (bacterio-)phage lambda virus is a simple example of this.

 

There are non-functioning relics of HIV-like viruses in some mammalian genomes - it seems that such viruses eventually just become a permanent resident of the host genome, a sort of evolutionary equilibrium between host and parasite.