An introduction to modern astronomy's most important questions. The four sections of the course are Planets and Life in The Universe; The Life of Stars; Galaxies and Their Environments; The History of The Universe.
DNA and RNA
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Confronting The Big Questions: Highlights of Modern Astronomy
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Are we alone in the Universe?
Planets and Life in The Universe - Exoplanets searches, exoplanet census, astrobiology
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Adam FrankProfessor
Physics and Astronomy
Welcome back, everyone.
So today we're going to talk more about the basic
building blocks of life in particular DNA and RNA.
Now you know, I am not an expert in this by any stretch of the imagination.
But any astronomer who wants to understand the
formation of life in the universe has to at
least aquaint themselves with, with the, the, the basics
of, of how life on this planet was born.
Because even if it's life on other planets doesn't take this the same specific route,
that has occurred on the earth.
The lessons about self replicating molecules are most likely it's hard
to image how to get life without some form of self replication.
So, we certainly learn very important things
by understanding what has happened on earth.
Okay, so what is, what are DNA and RNA?
they are essentially nuc, what are called nucleic acids.
and they are the main building blocks of life.
And what
they're building out of, you know each nucleic acid is a
nuc, nucleotide and it consists of you know, molecule or complex molecule.
That has five carbon sugar, which is again that particular kind of model molecule.
And at least one phosphate group.
So phosphate group clearly has phosphorous in it.
And what's also called a nucleobase.
And so this is just sort of you know
this, this structure, this skeleton of a molecular skeleton.
Out of which you're
going to build more complex molecules. Okay?
So, the difference between DNA and RNA so that's important, DNA, the
sugar is what's called deoxyribose and RNA, the sugar is what's called ribose.
So the sugar is just part of this skeleton.
Okay.
So we can think of both RNA and DNA as this scaffolding which has these bases.
And the bases are basically they're sort of, you know connection points
in some sense.
and these bases, there are four possible bases, both for DNA and RNA, but
DNA has they're, they're different for DNA and RNA or just by, by one.
So the nucleobases for DNA are Adenine, Thymine, Guanine and Cytosine.
And the nucleobases for RNA are the same except
you take out the thymine and, and put in uracil.
Now these nucleobases are going to be really
important because essentially in DNA what you
have is that beautiful double helix structure.
And what the helix what allows the helix
to stay together are these pairs of the nucleobases.
it's like a zipper essentially, with each side of the zipper
being, you know, each link being a different a base pair.
And the base pairs only connect in certain ways.
And that's what's really remarkable
about that.
So, what happens in replication, what reason why DNA is such a great molecule
for storing information, is that the, base
pairs because they only combine in certain ways.
Say for example, you can only get adenine and thymine or cytosine and guanine to
pair, is that it means that there's a very specific way for putting DNA together.
And if you take it apart,
there's only certain ways you can put it back together.
So what RNA does is it unzips a DNA molecule
and then new nucleotides will attach to form copies of it.
So you can both come pull it apart and make copies of it, or read off the
information that's in the base or in the DNA
in order to perform the str, functions of life.
So, RNA and DNA together are instructions for creating and
replicating living things.
So, one way to do is sort of think of the DNA as the hard drive.
Right, of where you store the information, and RNA, RNA is what
helps sort of take that information and do something interesting with it.
So the DNA always encodes informations.
For information for the cells about how to make proteins that are part
of the cells function and the RNA will carry it around into the cells.
So, what makes DNA so important is that together DNA makes genes.
And genes are the mechanism for heredity.
Right, so DNA is the molecule for heredity.
It's what determines what functions, what characteristics can
get past from one generation to the other.
so the only thing that really separates you from, say you
know, a slug is basically the information encoded in your DNA.
It's just the different kinds, arrangement of the base pairs.
And that's what's really remarkable.
So, in the, the history of life has really been
a history of passing characteristics along through DNA and RNA.
And we would expect that something like this has to
occur in some form on life on other planets as well.
There must be some chemical basis for life
that includes something like passing along inherited characteristics.
So, using this idea of heredity and DNA biologists can
put together what they call the Phylogenetic, or Evolutionary Tree.
And really what it does, it's using DNA.
It allows biologists to determine how closely related two organisms are.
In sort of the spread of evolution,
and the spread of ke, new characteristics forming.
their closeness isn't really a relationship determined
by the distance from their closest ancestor, right?
So for example human beings and the great apes, had a common ancestor
a few million years ago, okay?
And it can keep you know, sort of put in these, you know,
trying to build these trees until you could find the earliest ancestor of life.
now, of course some of that you know, the truly
earliest ancestors are probably completely lost in the evolutionary record.
But, you know from, we can already see that
there must have been this, from the, the record.
So we see that animals are more closely related
to fungus and slime molds than they are to plants.
We also see there's two different kinds of bacteria.
There's green bacteria and
purple bacteria.
so all this comes out of studying DNA, studying the variations in DNA.
And one of the interesting things about this is that
we expect if we would have find, say, life on Mars.
The big question we would want to ask is, does it have, does it fit
unto all phylogenetic tree or is it
part of an entirely different phylogenetic tree?
Some people believe that life may have actually started on Mars.
During the first half billion years of its existence
because it was quite warm and wet in those days.
And perhaps an asteroid impact may have blown a chunk of Mars with bacteria on it.
Over to earth and that's where life began on earth.
And so we might, the, if that were the case,
if we were to find bacteria on Mars and we were
studying it, we would find actually that it
was part of our phylogenetic tree.
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