2.6. The Genetic Code and Evolutionary Theory

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Emergence of Life

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University of Illinois at Urbana-Champaign

Emergence of Life

58 個評分

How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life! This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include: -Reconnaissance of ancient primordial life before the first cell evolved -The entire ~4-billion-year development of single- and multi-celled life through the lens of the Tree of Life -The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.

從本節課中

Week 2 - The Tree of Life and Early Earth Environments

The advent of life on Earth came about as a result of a remarkable confluence of physical, chemical, and biological processes, all of which were intrinsically linked to rapidly changing early Earth environments. Within this context, cutting-edge approaches in molecular phylogeny by Professor Carl Woese revealed new understandings of the emergence of life and the possible distribution of life within the cosmos. All this and more will be explored in this week's lessons!

2.1. The Scientific Inquiry of Carl Woese8:00

2.2. The Place of Carl Woese in Evolutionary Biology8:24

2.3. Revolution of the Tree of Life7:41

2.4. Evolution of the Tree of Life6:42

2.5. How Did Life Emerge?5:25

2.6. The Genetic Code and Evolutionary Theory7:23

2.7. Throwing Rocks at Earth: The Martian Meteorite10:46

2.8. Microbial Mats and Stromatolites: Laying Down On the Job6:49

2.9. Oxygenation of the Atmosphere5:15

2.10. Snowball Earth; It Did Freeze Over!8:31

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Bruce W. Fouke, Ph.D.
Director of the Roy J. Carver Biotechnology Center
Department of Geology, Department of Microbiology, and Institute for Genomic Biology

[MUSIC]

So in today's lecture, I'm going to talk about evolution before there were genes.

So, this is the genetic code and it's a remarkable code for many reasons.

The first reason is that a genetic code is universal.

We have the same genetic code, as jelly fish.

We have the same genetic code as corn, as pigs, as elephants.

Every animal has the same genetic code.

That's how we can do genetic engineering, which you've doubtless heard about.

We all have the same genetic code.

So take genes from a jellyfish, stick them in you, you'll glow green.

Isn't that great?

So you couldn't do that, if we had different genetic codes.

So that's the first attribute of the genetic code, that it's universal.

Now, there's a second one that really was only fairly recently discovered going back

about 20 years or so and this is the following.

The genetic code is extremely good at minimizing errors.

So let's suppose there's been a mutation, so the sequence in or

genome has been slightly screwed up.

Or let's suppose that the translation apparatus doesn't work very well,

makes a mistake.

You're going to get the long amino acid.

If you get the long amino acid, you'll get the long proteins.

If you get the long proteins, you'll die.

That's not good.

So wouldn't it be great if you had a genetic code that if you make a mistake,

the amino acid that you get is going to be pretty close

to the one you should have got.

And therefore, hopefully, it won't make too much difference.

So, guess what?

Our genetic code is pretty much as good,

as it can possibly be at minimizing those sorts of errors.

So it's really, really good at mitigating the effects of this kind of misreading or

this kind of mutation.

In some sense, we'll say then that the genetic code is optimal.

It's not truly optimal, but very, very close to optimal.

I want to answer the question now of how

it came to be that the genetic code had this structure?

Now you might just say, well, the genetic code is optimal, but how good is good?

How good is very good?

How likely is that to have arisen by chance?

Well, we knew the answer to that.

I can't explain to you in this lecture how we know it, but the probability of

this happening by chance is much less than one part in a hundred million.

So something happened, something special happened and

what happened was that the genetic code evolved.

In fact, it evolved before the last universal common ancestor.

It had to have evolved before the last universal common ancestor.

Because if it evolved afterwards,

we wouldn't be able to do molecular phylogeny to look at the translation

apparatus to deduce the existing of a last universal common ancestor.

So we know there was life before the last universal common ancestor and

we know that during that period of time when life was starting to sort of get

going, the genetic code evolved and it must've evolved very rapidly.

So 3.5 to 3.8 billion years ago, we had a full functioning genetic code.

So question,

what evolutionary mechanism is there that can evolve things so fast that something

as complicated as the genetic code could evolve in a very quick timescale?

Well, I've already told you the answer in this lecture.

There's only one thing that can do it and that's horizontal gene transfer.

So, the same mechanisms that are causing the bacteria in your gut to evolve

rapidly and defeat the medical community's attempt to counter bacterial infections.

Those same generalized evolutionary mechanisms

gave rise to the evolution of the genetic code and

the evolution of the cell more than 3.5 to 3.8 billion years ago.

[MUSIC]

>> Darwin shifted the question of evolution to the origin of species and

focused on the origin of species as in the title of this book.

Not big truth, not the big universal tree of life.

But Darwin argued in order to have a deep evolutionary by large and

deep evolutionary genealogy, that is classifying organism naturally in

terms of the way in which they evolved and the course of evolutionary history.

One had to distinguish between trivial characteristics and

the essential characteristics of an organism.

Again, Darwin's world was a world of plants and animals and

how you did this with animals was easy.

Well, it was not easy, but it was easy in the sense that there were morphological

traits that were deep in the organism.

So Darwin argued the best way to do it was to look at embryonic characters,

because those characters would evolve very, very gradually.

And they may, in fact, be stable, highly conserved in evolutionary time.

Whereas adaptations would be piled on top of these deep,

highly conservative developmental characteristics.

Well, none of that was available from microbes.

Microbes didn't have NPO's.

They didn't have great morphologies and the way in which one classified,

ever since Darwin was a comparative morphology.

So now we're caught in another false dichotom, just like the plant animal one

that we tried to group all of life into or one between the prokaryote and

the eukaryotes that we tried to group all life into,

even in our evolutionary concepts or conceptions of life on Earth generally.

We have this other dichotomy and that dichotomy is are you a Darwinist?

Or are you a creationist?

Creationist meaning that you invoke supernatural phenomena on Earth to account

for the course of evolutionary time that you don't believe we are of this Earth.

We're created in some other fashion, but not by natural processes on this Earth.

So, the problem with that dichotomy is that evolution and

Darwinism are conflated.

They're seen as one thing.

To pose the question, are you a Darwinist is to say, you are an evolutionist.

If I say, are you an evolutionist, the automatic response is you're a Darwinist.

And so what I'm saying is that we have to break away from that dichotomy,

because it's a false one and that we can be evolutionists without being Darwinist.

And we have to understand that our principles of evolution have to evolve and

they evolve with the data, and we've only got begun to have access, and

we're just scratching the surface of the great diversity in the microbial world,

and there may be other things afoot.

Like Carl Rose likes to talk about a cosmic evolution.

I mean, I've always believed that evolution is bigger than life,

way bigger than life.

You have evolution first and then you think about life.

And if that's true,

then we have to think of cosmic principles through which life is formed.

Life is not an accident.

>> So, I think a hundred years down the line,

people will know Woes' name,

just like we know Darwin's name a hundred years down the line.

[MUSIC]

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