This is sort of a mystery. Back a very, very long time ago there were no living creatures on Earth, just a kind of swamp. At some point, the first short DNA sequence must have spontaneously arisen. This means that somehow all the molecules required to make DNA randomly came together and the first DNA was formed.
This piece of DNA must have been able to replicate to produce more copies of itself. Over time, changes would have occurred which made this DNA more complex and at some point able to form a cell and create a living thing.
This is how I assume it happened. Creating life out of a bunch of molecules is a pretty extraordinary thing. Once that first piece of DNA was made though, it was just a matter of survival and evolution to turn it into all the living that have ever existed.
Big question. One of the last big questions remaining in science is how did we originate from simple stuff.
Step 1 – what happens if you get together a bunch of really simple molecules and you put them in a pot that pretended to be the early earth – water, lightning, that kind of thing? A guy called Stanley Miller did just that. He got together a bunch of chemicals, heated them, passed electric sparks through it and waited about a week. At the end he analysed what he got – a bunch of naturally-occurring molecules called amino acids had been formed.
So this showed you can make molecules we see around us in nature by random chemistry under conditions that were like the early earth. Give enough time, you could probably get quite complex things.
Step 2 – can molecules that look like the bits of DNA be formed under these conditions?
Yes – people have been working on this and slowly getting together examples of ways that the bits of DNA (the “bases”) can arise randomly. Here’s a link to a recent important set of experiments:
You won’t be able to read the paper – you have to pay to read it, sadly, but you can see the kind of thing they’re talking about.
Step 3 – If DNA (or its relative, RNA) could form, could it replicate itself? Answer is yes – people have seen this kind of stuff. Here’s a link to another paper where they show a strand of RNA making itself (and making itself better than making other things)
So you get this amazing picture – very simple molecules can make more complex ones, and these complex ones can form into chains that can then help to make more of themselves.
Though we can’t ever see this happening on the earth (it’s already happened) we can get together all this evidence that it could definitely have happened by a series of logical, easy steps that needs only time.
Now if you want to go from DNA to a cell, and to an organism, there are more steps. For a cell you need to have a compartment, separated from the rest of the world. That’s a really tough, unsolved mystery – how did the first cells start? Big science, that. Really interesting mix of chemistry, biology and physics. If you want to read about it Google “coacervation”
What’s kind of neat is that DNA is designed to replicate itself. The way the double helix works – one strand is a perfect template for the other. The way the molecule is put together makes sure of this – you’ll learn about the “hydrogen bonds” when you study it a little bit. It’s really very pretty. When you look at it that feature – that one strand templates the other one – makes you think “yes, this thing is used to making itself”.
This is sort of a mystery. Back a very, very long time ago there were no living creatures on Earth, just a kind of swamp. At some point, the first short DNA sequence must have spontaneously arisen. This means that somehow all the molecules required to make DNA randomly came together and the first DNA was formed.
This piece of DNA must have been able to replicate to produce more copies of itself. Over time, changes would have occurred which made this DNA more complex and at some point able to form a cell and create a living thing.
This is how I assume it happened. Creating life out of a bunch of molecules is a pretty extraordinary thing. Once that first piece of DNA was made though, it was just a matter of survival and evolution to turn it into all the living that have ever existed.
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Big question. One of the last big questions remaining in science is how did we originate from simple stuff.
Step 1 – what happens if you get together a bunch of really simple molecules and you put them in a pot that pretended to be the early earth – water, lightning, that kind of thing? A guy called Stanley Miller did just that. He got together a bunch of chemicals, heated them, passed electric sparks through it and waited about a week. At the end he analysed what he got – a bunch of naturally-occurring molecules called amino acids had been formed.
So this showed you can make molecules we see around us in nature by random chemistry under conditions that were like the early earth. Give enough time, you could probably get quite complex things.
Step 2 – can molecules that look like the bits of DNA be formed under these conditions?
Yes – people have been working on this and slowly getting together examples of ways that the bits of DNA (the “bases”) can arise randomly. Here’s a link to a recent important set of experiments:
http://www.nature.com/nature/journal/v459/n7244/full/nature08013.html
You won’t be able to read the paper – you have to pay to read it, sadly, but you can see the kind of thing they’re talking about.
Step 3 – If DNA (or its relative, RNA) could form, could it replicate itself? Answer is yes – people have seen this kind of stuff. Here’s a link to another paper where they show a strand of RNA making itself (and making itself better than making other things)
http://www.sciencemag.org/content/323/5918/1229.abstract
So you get this amazing picture – very simple molecules can make more complex ones, and these complex ones can form into chains that can then help to make more of themselves.
Though we can’t ever see this happening on the earth (it’s already happened) we can get together all this evidence that it could definitely have happened by a series of logical, easy steps that needs only time.
Now if you want to go from DNA to a cell, and to an organism, there are more steps. For a cell you need to have a compartment, separated from the rest of the world. That’s a really tough, unsolved mystery – how did the first cells start? Big science, that. Really interesting mix of chemistry, biology and physics. If you want to read about it Google “coacervation”
What’s kind of neat is that DNA is designed to replicate itself. The way the double helix works – one strand is a perfect template for the other. The way the molecule is put together makes sure of this – you’ll learn about the “hydrogen bonds” when you study it a little bit. It’s really very pretty. When you look at it that feature – that one strand templates the other one – makes you think “yes, this thing is used to making itself”.
0