[Lecturer] Hello, and welcome to the third
and final lecture in module two.
Congratulations for making it this far. (chuckles)
Hopefully your head's not spinning too much,
and the information is starting to soak
in a little reinforced through the reading in mostly
in the textbook chapter that excerpts
from the textbook chapter that I wrote.
There isn't that much information in the textbook
for the class on this material.
There's just a few pages,
and in my opinion, it can be a little bit confusing
because it's lacking the detail.
I think it's necessary for you
to understand what they're trying to convey there.
So hopefully you're getting that through the text
in the posted reading,
and the lectures are serving to reinforce
that and to provide you some more detail
and some more color on all of that.
And just, again, remember, this isn't the end
of this material.
We're going to keep coming back to it.
So if it hasn't all fully soaked in
with you yet, just know it will, it absolutely will.
This is the beginning of this semester for this course,
and it will keep coming back up
and in different ways, in different contexts.
And I think, you know, through continued exposure
and exposure in different ways, it will really start
to soak in and not only soak in,
but also start to become clear how this is relevant
for you and for your practice.
But once you have the basics down, then the rest
of it will really start to fall into place.
So let's start talking about the central dogma.
Comes up to the question of what does DNA actually do?
And why is it really that important?
DNA is like the blueprint for life.
It gives instructions for all cells to make all
of their proteins that they will ever make.
So at the very moment of conception, when an egg
and sperm fuse, and you have the full complement of DNA
for an individual that contains all of the instructions
that single cell will need to turn
into an adult fully functioning human being
after development and all of
that, it basically provides all the instructions
that any and all cells that form from
that one original cell will ever need
to make all the proteins it will ever need.
To me, that's pretty astounding to think about.
At the very beginning, all the information is there
and it will happen and it will develop
if given the right environment.
A region of DNA strand that gives the instructions
for making a single protein is called a gene.
So this is how we're defining gene.
It is the unit of inheritance,
and one gene equals the instructions
for making one single protein.
And this is just to a small recap
from what I think was covered in the previous lecture
as well, but just want to reinforce here, one gene, the way
a gene is defined really is that it is a sequence of DNA
and that sequence will provide the instructions
for making a single protein.
Proteins perform virtually all functions
within the cells, tissues, and organs.
And we talked about this already,
but just want to reinforce that's the case.
You have lots of different types of proteins,
of course, just giving a couple examples of proteins
that you can think of insulin, keratin,
neurotransmitter receptors.
I mean, there are thousands and thousands
and thousands of different proteins,
and they all perform very specialized
and distinct functions.
So we have about 25,000 genes in the human genome.
So, but we do actually have more
than 25,000 different proteins.
So how does that work?
You probably are wondering, and rightly so.
Well, again, this is the majority rule
versus the exception rule.
And if we're going on the majority here, the majority
of genes will code for one single protein.
However, proteins can also form different structures
by taking subunits of proteins.
I mean, there's a lot of complicated biology
that can happen, and biochemistry that can happen.
Modifications of proteins
often occur, which can give them distinct functions.
But in general, what we're talking about here in general is
that a single gene will give the instructions
for the cell to properly form one protein.
Genes are made up of bases, as we talked about
in the last lecture, adenine, thymine, cytosine, guanine.
Your four buddies, A, T, C, and G.
So genes are made up of these bases
in a particular sequence.
And the sequence is an arrangement of bases,
like a word made up of specific letters.
So if you're thinking about this,
here's a different metaphor for you, you can think
of the bases as the letters,
and they kind of are, makes it a little simpler
to think of it this way because we represent them
as single letters, but you can think of them as letters,
and you could think of the gene as either a word
or a sentence, say for example.
And that's made up of the right sequence, the right order
of letters.
If something is in the wrong order or missing something
or has something added to it, it would be a different word,
it would be a different sentence.
It would have completely different meaning.
Very similarly here, the sequence, the order
in which As Ts, Cs, and Gs appear
in a gene, it will affect the instructions
for that formation of that particular protein.
So DNA has a pretty cushy job.
You know, it itself doesn't actually do all that much.
It's like the boss, it sends out instructions
from its cushy office in the nucleus.
It's sitting in the nucleus.
It sends out instructions into the cytoplasm
of the cell, and it provides instructions
for other things, you know, other components
to actually do the work of making proteins.
And the proteins are the workhorses.
So they go out and they actually do all the work
in the cell while the DNA sort of sits there
in the nucleus, very protected, which it really has
to be protected because the sequence is quite precious given
that it, the sequence has to be copied with high fidelity
from one generation to the next thousands
and thousands of times over,
if you consider how many times your cells divide
within your body.
So it has to be protected, it's very special,
very precious information.
And also it's gonna be passed on to the next generation
and the next one after that, and the next one after that.
So it needs to be protected and it needs to remain safe.
And in order to do that, it's kept very distinctly
within the nucleus of the cell.
But in order for it to function, it has
to send out these messages
into the cell cytoplasm to tell it how
to basically make all the proteins it needs to make.
The sequence of a gene is copied from the DNA
in the nucleus into a molecule called mRNA.
This stands for M for messenger. RNA is ribonucleic acid.
So this is messenger ribonucleic acid.
The mRNA is transported out of the nucleus
to the protein assembly line where it is used
to instruct how ribosomes assemble proteins.
This process is called translation.
So the first process of copying the DNA
of a gene, the sequence of a gene to mRNA.
So making a copy of it doesn't actually do anything negative
or any way affect the DNA strand itself.
It's just simply making copy, like going
to the library, taking a book, making a photocopy of it.
You know, say like, I think I used this metaphor
in the textbook chapter that that's posted for you to read,
but it's like a reference book at a library,
if you remember what libraries are. (laughs)
Again, I keep using these metaphors and I'm thinking, well,
we don't really use corded telephones and nobody really goes
to the library anymore, but okay, let's assume
that you still go to the library and you want
to look up some information in a reference book
and say something that you can't check out
of the library because it's too precious.
What you could do instead is take it
to the photocopier machine, sit it down
on the photocopier, scan it, take a copy of that,
and that's what you would take out of the library with you.
Let's imagine for a second that the nucleus is
like the library, where in order to get the information
from the nucleus or the library, you go into it, you take it
and you scan a copy, you make a copy
without harming the reference book, which in this case,
in this metaphor would be
like DNA, you're not harming it, you're not destroying it,
you're not taking a part of it,
you're just simply making a copy of it, take a copy of it.
In this case, the copy, the photocopy would be the mRNA.
So it's just a duplicate, essentially
of the DNA sequence.
It can actually leave the nucleus
because it's just a temporary thing,
like it's just a temporary stretch of nucleic acids,
that matches the sequence of that particular gene.
So it can leave the nucleus, that's no problem.
It does, it leaves the nucleus.
So that would be like you taking your photocopies home.
And let's say
in this particular case, it was a reference book
for how to build a bicycle.
You make your copy from the reference book
on how to build a bicycle.
You take that out with you back home.
In this case, going home would be sort of
like leaving the nucleus and going
into the cell cytoplasm where you'll use your tools, say,
your toolbox, your toolkit
for building a bicycle would be really like the ribosomes.
They're going to read the instructions that copied
in this case, like mRNA,
that ribosomes are gonna read the mRNA, that copy
of the sequence, and that's going to tell them how
to assemble that specific protein properly.
Copying the sequence to mRNA is called transcription.
And when the copy or the mRNA is read,
and that instruction is used for making protein
or protein synthesis, that process is called translation.
Let's take a quick peek
at proteins you're probably quite familiar
with certain proteins that are very clinically relevant,
but proteins are made up of a chain of amino acids.
So they're also like a long chain that what we're looking
at here, in this case, this is like a schematic
of a structure using like molecular structure
of a particular protein.
And it is a long chain,
but you can see this doesn't look like a long chain.
This is kind of bunched up and curled up,
and that's absolutely true.
It's formed as a long chain of amino acids.
One attached to the other, attached
to the other, attached to the other.
But then after that, each amino acid has
a very unique chemical structure such that
after the long chain has formed, the protein will start
to fold in on itself and it will form grooves
and it will form very specific shape
to it, which is necessary, completely necessary
for its proper function.
In the case
of proteins structure absolutely determines function.
Structure determines function
and structure of a protein is determined
by its amino acid sequence.
So if we're looking at the schematic
of a protein, say this is basically just showing you a bunch
of different amino acids that are all connected together
as a long chain then folded up on itself.
So protein is just made up
of individual units called amino acids
that interact and fold up on itself
to form the final structure of the protein.
And that structure determines the protein's function.
Its ability to do what it needs to do
within a cell, which is so important.
This is where disease happens because proteins are critical
for every function in the human body.
You can't think of one where a protein isn't necessary
or used in some particular way.
So if a protein happens to have the wrong amino acid
in the wrong place and it can't fold properly, can't form
the right structure, guess what?
It's not gonna have the right function, it's not going
to function properly.
So then that leads to disease.
Okay, let's take a look over here.
So we've talked about amino acids must be the correct ones,
and then the correct order for the protein
to function properly or at all.
Even a single change
in amino acid can disrupt the protein's function.
There are 20 different amino acids, proteins vary greatly
in length, but median length
of a protein is 361 amino acids, but take my word for it.
And they can go from, (chuckles) you know, very short
to really, really long 361 is just the median length
of proteins.
Central dogma, this is a weird phrase, right?
When are we're talking about central dogma, again,
it sounds very philosophical
and maybe even a little religious or something,
but actually, it's not, it is a really key insight
into molecular biology
that is sounds simple when we think about it now,
but was so impactful in the way
that we understand really everything
that functions on a molecular level.
It was first stated by Francis Crick in 1958.
As you can recall, Francis Crick was part
of the Watson and Crick duo
that originally described the structure of DNA.
So it was a very busy guy.
And in 1958, he stated
for the first time that, hey, you know what?
Maybe this is the way DNA functions DNA to RNA to protein.
And what do I mean by that?
Well, this just means this is the flow of information.
So DNA is copied into RNA, RNA provides instructions
for making protein, it always goes this direction.
It always goes DNA to RNA to protein.
You never have protein going back
and informing the instruction of RNA and RNA going back
and somehow affecting the structure of DNA.
Never, never, never, always.
And this is, hey, this is one
of the times I can actually say always (laughs)
and I don't have to say, well, except, and
from all we really understand now, it does always go DNA
to RNA to protein.
Part of the reason for that is what I've been saying,
what I was saying before, which is that DNA is precious.
That's the material that gets passed on.
That's the unit of inheritance from generation
to generation within your own body,
from cell division to cell division.
That is the part that is always going
to be there and always going to be the same.
So we need to protect it.
So it always goes DNA, instructing RNA,
instructing protein formation.
DNA is copied into a complimentary strand of messenger, RNA.
The mRNA is used by ribosomes
in the cytoplasm outside of the nucleus to tell it
to assemble which amino acids and in what order
to properly form a protein.
And remember the right order of amino acids determines the
right function of that protein.
Really, really critical. And again, this is the order.
So step one, this is called transcription.
Step two, this is called translation.
Always goes in that order.
Transcription first, translation second, you have
to make the copy before you can use it to make the protein.
I just wanna make sure that it's very clear here
because I know this is a common misunderstanding
that can happen when we're talking about
DNA to RNA to protein.
DNA does not become RNA, DNA is used to make a copy
that is housed in a molecule called RNA.
RNA is a separate molecule from DNA.
It's just used to make a copy of the DNA.
The RNA does not become protein.
The RNA is used as an instruction,
and we'll talk about
that when we talk about specifics of translation.
But RNA is used to provide directions for how
to properly make proteins.
Proteins are made up of amino acids.
Amino acids are very, very different
from nucleotides, which make up RNA and DNA.
Just wanna make sure that that's pretty clear.
All right, let's take a quick peek
at a schematic of the cell.
And when we're talking about transcription and translation.
DNA in the nucleus, we all know this,
we all love this fact, right?
DNA in the nucleus of the cell, transcription happens.
This is, we'll talk about this in more detail,
but you can start to think of it
as basically one of the two strands.
Remember DNA's double stranded, right?
One of the two strands is used
to make a copy of it, a complimentary copy of it.
Remember what complimentary means?
A binding to T, binding to G.
There is a slight exception here,
and we will talk about that in just a moment.
But basically this is what happens during the transcription.
mRNA is formed as a copy of DNA.
This is completely different molecule does not destroy
in any way, mark or is any way detrimental
to DNA, it's simply copying it.
The mRNA, which is a very short strand compared
to really, really, really long DNA strands,
this is not showing it to scale.
DNA strand, as we've talked about, you know, can be really,
really, it's really, really long.
mRNA is just the length
of the gene, just the length of one gene.
That's the length of the mRNA
because you only need the one gene.
'Cause one gene instructs the formation of one protein.
So mRNA is formed, mRNA is free
to leave the nucleus while DNA is stuck in the nucleus.
mRNA can leave 'cause it's really a short strand
and it also has certain modifications
to it, the DNA does not have, which allows it
to leave the nucleus, so mRNA leaves the nucleus.
So this first step here is called transcription,
making a copy of a sequence of one gene from one
of the strands of DNA into mRNA.
That's transcription, mRNA leaves the nucleus.
And here's where we start to talk about translation.
So how do you get that message
of the DNA sequence which was copied
into mRNA, into protein?
Well, the cell has come up
with a really cool way to do this.
It's actually using code, a code of information
that's housed in the specific order of the bases.
Remember the bases are As, Ts, Cs, and Gs?
The specific order of those which can be found
in the sequence is used and is decoded
to determine the specific amino acid sequence.
What do I mean by that?
Well, the cell has come up
with a specific code where it knows
and it does this in sets of three.
So if you think about it, I don't know,
if you as a kid or you know, if you have children,
if you've ever done this
with them, where you could get like a decoder ring
and you know, you can take the hidden message
and figure out what it actually means.
You know, so this symbol equals A, this symbol equals B,
this symbol equals C.
And you know, you can kind of figure it out
and piece it together, you're breaking a code.
That's exactly what the cell is doing.
The cell is taking this, the specific order
of As, Ts, Cs and Gs and it knows this particular sequence
of bases equals this particular amino acid.
This other sequence of bases equals this other amino acid.
And when I say equals, it means the DNA is trying
to tell the cell that this is the proper order
in which the amino acid sequence should occur.
It does this through a protein complex called ribosome.
Ribosomes will actually bind directly
to the mRNA in the cytoplasm
and using other molecules, which we won't talk about
in a lot of detail 'cause it starts to get pretty technical.
But another molecule called tRNA
or transfer RNA, which has three bases on it.
Which when it binds, remember binding
and base pairing from the DNA double strand?
This is occurring here as well.
But in very short segments, in segments
of three bases at a time, three bases at a time.
That's called that triplet of bases is called a codon.
The reason why it's called a codon is
'cause it codes for a specific amino acid.
Three bases in a specific order will give the instructions
for one specific amino acid.
Three bases equals code for one amino acid.
And the tRNA is really what is the missing link there.
So it has three bases, which it's complimentary
to a specific codon and it attaches itself
to a specific amino acid.
And that way it knows it can come in
and the particular, say tRNA, which has attached
to it, the amino acids say glycine will only bind
to the triplet of nucleotide.
So the three base sequence that corresponds to glycine.
And the ribosome will actually kind of glide
along the messenger, RNA from one end,
specifically one end to the other end.
And as it glides along,
it will read each triplet three at a time.
So it reads this three, for example.
Then it would hop over
and read the next three, read which amino acid
that is using tRNA and then it would hop over
and it'll read the next set of three.
Find that right tRNA with the right amino acid.
And all along these amino acids, the tRNA is being released,
but the amino acid stays behind
and it gets attached using the ribosome
to the previous amino acid.
So you're left with is a long chain of amino acids
that all corresponded to the particular codon
of the mRNA as as the ribosome has moved along it.
This whole process is called translation
or protein synthesis.
Alright, take a second to soak that in (chuckles)
and we're gonna talk about it in more detail now.
Transcription. Let's go back to that.
This is that first stage. Proteins called RNA polymerase.
You don't really need to know the name of it,
but I figure you should at least be exposed to it once.
So proteins called RNA polymerase will bind to one strand
of double stranded DNA within a gene.
And the one strand that it binds
to is called the antisense strand,
and it will make a complimentary strand out
of ribonucleic acid called mRNA.
This is a similar structure
to DNA except it's always single stranded.
RNA is is really, there are some exceptions to
that are important exceptions,
but not for the context of this class.
In the context of this class,
you can just assume RNA is going to be single stranded,
and mRNA really is single stranded.
So it's similar, but instead
of a deoxyribose sugar, it has just a ribose sugar
that it's less likely to form a double stranded structure.
The other difference is that instead,
so while mRNA has very similar nucleotides
to DNA, the bases are similar there.
It has G, it has C, the only exception is T.
So thymine instead of thymine mRNA uses uracil
or the letter U you can replace there.
So anytime you see a T
in the DNA sequence, when you're thinking about
what would the RNA sequence be for that?
You can replace that T with a U.
The reason why it needs to do that is because having uracil
or U present in the sequence targets it
for transport out of the nucleus, that's important.
And it's important that DNA does not have U
or uracil in its sequence
because otherwise DNA would escape the nucleus
and it would no longer be protected
in its nice little environment in the nucleus.
Instead, mRNA has uracil instead
of thymine, which then allows it to escape the nucleus
and get into the cytoplasm for translation.
Okay, so I think we covered the rest of this.
It's single stranded has only one strand and is short.
Oh, right, it's short.
So it's only the length of a single gene.
And as you recall, a gene, a single gene takes up
a very small stretch of the total length of a DNA strand.
The mRNA sequence is complimentary
to the antisense strand and identical
to the sense strand, again, except U replacing T.
So when we're talking about the being complimentary
and identical, we'll look at that on the next slide.
But just think of it this way
and sometimes, let me just say, sometimes
in genetics we use some strange terms like antisense
and sense, there's usually some logic to it though,
so when we say antisense strand, it binds
and copies the antisense strand.
So it's going to be complimentary to that,
which means it's going to be identical to the other strand.
If you're complimentary
to the complimentary strand, (chuckles) it's going
to be the same as that original strand.
It'll sink in a second.
I wanna show you the next slide hopefully,
but just think of it that way.
So mRNA sequence is complimentary
to the antisense strand and identical to the sense strand.
Let's look at an example of what the heck I'm talking about.
Okay, again, let's say this is your gene here,
again, most virtually all genes I can confidently say
all genes are gonna be longer than this,
but it's just to give you a sense of scale.
Let's say this is your DNA strand.
Remember, DNA in the nucleus is normally compacted
into chromosomes.
So we're just stretching it out here
so you can kind of see what's going on.
If we stretch out, you can see
that the two strands, which are normally bonded together
right through base pairing are separated slightly here so
that the two strands are separate from one another.
And RNA can start to form a complementary strand
to the antisense strand using RNA polymerase,
which is this blob here that's coming along
and it goes in a specific direction.
In this instance, it's going from left to right.
So it's going from this side to this side.
The RNA polymerase is moving along
and as it hits particular base,
so let's say it's hitting this particular
guanine here in the antisense strand, it's going to read
that and it's going to know, okay, we need a cytosine.
'cause cytosines going to be complimentary to guanine,
remember C binds to G.
So it will put down a C here.
When it reaches this adenine, this A here.
Remember, the complimentary base
in DNA would be thymine or T.
But since we're talking about RNA,
what replaces thymine in RNA?
That's right, it's uracil or U.
So instead of putting down the base T here,
which you would see is present
in the sense strand, it would use a U.
So the next bases,
you can always predict what it's going to put down.
If this is a C here, it would go GCC UUA ACC GC.
Do you get what I'm saying here?
It's complimentary to the strand.
And you can start
to see why this is called the sense strand.
While there's no, there's nothing going
on here, there's no activity going on
on this strand, it's not being copied.
But what is happening, the sequence identical
to it is being created because the sequence complementary
to the antisense strand is what's being made.
So it moves along until it reaches the end of the gene.
And this is where the mRNA will fall off.
The single stranded mRNA will fall off of the DNA.
The DNA will bind back together.
So the two strands will come back together
and will fold itself right back up
into, its tightly wound chromosome formation
and the mRNA will leave the nucleus.
Let's move on to translation.
mRNA exits the nucleus and reaches ribosomes, ribosomes bind
to mRNA and facilitate protein synthesis using complementary
molecules called tRNA, which bring a specific amino acid
to match a specific mRNA codon sequence.
Remember, codons are sets of three bases along the mRNA.
The tRNA as I mentioned before, it's kind
of the missing link, the bridge
between nucleic acid and amino acid.
So it has an amino acid attached to it,
but it also has a sequence a codon which will bind
to a specific codon and will deposit its amino acid
into the growing protein chain
that is housed on the ribosome.
The ribosome will move
in a specific direction along the mRNA
and will basically shoot out the protein as it goes along.
The ribosome will continue to move along the full length
of the mRNA molecule until it reaches a specific codon.
So remember, codon is a triplet of bases.
So until it reaches a specific sequence called a stop codon,
where it's told to essentially fall off and it does,
and the protein has been completed.
Breaking the code.
So this really is like the code breakers of World War II.
This is kind of the same approach that had to be taken
to figure this code out.
And it has been, and it is very consistent.
We're not talking just
in humans, we're talking about all living species
is just astounding to me how highly conserved this is
across literally every living species
that's been explored has the same code.
How cool is that?
That, I mean, just billions of years of life in evolution.
It has continued to remain identical throughout that.
The base sequence of a gene contains coded information
for ribosomes to make proteins properly,
which is what we've been talking about here.
And the bases are read from mRNA sequentially
in groups of three called codons.
So from just giving you an example of a stretch
of mRNA sequence from reused, replaced Ts
from the DNA sequence, we would read the codons
as follows, AUG/CGU/GGU/AAC/GUA.
So it goes in sets of three, it reads this set
and it moves to the next set of three, and then it moves
to the next set of three and so on and so on.
AUG is universally recognized by ribosomes
as a signal to start translation.
So all proteins start with methionine
because the tRNA, which recognizes AUG, carries
with it the amino acid methionine.
Each codon codes
for specific amino acid except the three codons,
which tell the ribosome to stop translating.
That doesn't have a corresponding tRNA.
And as a result, the ribosome just kinda gets stuck there.
It's like, oh, okay, I guess we're done.
And it sort of falls off.
And then the protein, the chain of amino acids,
which is the protein can go along its way
and form its structure and do its function.
The three stop codons are UGA, UAA and UAG.
Given that there are four bases,
so A, U, C and G four bases in RNA and three positions
for a base per codon, because a codon is a triplet
or three bases, there are 64 possible different codons.
So four to the third power,
but there are only 20 different amino acids.
So most amino acids actually are coded
for by multiple codons.
So it's not just a single three base sequence
that codes for a single amino acid.
One amino acid can have multiple different codons
that code for it.
This can be a good friend for you
if you're ever doing any work where you need
to decode a specific sequence
to understand what the sequence is coding for.
So which amino acids it's coding for.
This is called a codon table.
And you can find it, you can Google it.
It'll come up, I think there's one in the textbook.
There's one in the excerpts from the textbook
that I included as well.
They're everywhere.
So just look for codon table, you'll find this.
The way you read this is, remember
there are three bases, right?
Three bases in a codon.
You have the first base along the left hand side here.
So vertically along the left hand side, you find, which
is your first base.
So let's say it's a C. Okay, there's C.
Then you need to know what's your second base.
Let's say your second base is an A, okay, well you look here
and then your third base, let's say is,
so we had C, A let's say your third base is a G.
So we would look under C, come over to A, G.
It says CAG, here it is. What is that code for?
Codes for glutamine.
This is giving you the letters are
the single letter designations for each of the amino acids.
Which is sort of a standard designation for each of them.
So you can look at it this way, you know, you can figure it
out that way you can also just kind of glance
through the chart if you don't want
to use the different columns.
Let's say, you know, you're looking
for what is AAG, oh, well here's AAG that codes for lysine.
Got it. Okay.
So this is a very handy useful table
that you can use in decoding DNA sequence.
So here are a few tricks
for quickly decoding a DNA sequence.
So if this is the DNA sequence.
Let's say this is these are the two complimentary strands
to one another, you can tell, first of all, this is DNA.
Why? Because there's thymine here and it's not uracil.
So we know it's DNA. No, it's not RNA.
So this is DNA,
and we know these two are complimentary to one another.
How do we know that? Well, because they are.
So A is complimentary to T. T to A, G to C, C to.
So we know these two strands are complimentary
to one another.
If we're looking at this DNA sequence
and we want to know what is the sequence
of amino acids that this is coding for?
What we can do very quickly is think
of, okay, well what would the RNA sequence be for this?
All you have to do is change the antisense strand.
T, anytime there's a T to a U and separating the codons.
What do I mean by that?
So the first codon, the first three triplet
of bases is ATG.
We change that to AUG because instead of Ts we have Us
in RNA sequence, then the next set would be CGG.
Well, nothing to change there. It's just CGG.
The next set is TAC, oh, there's T, it becomes U, UAC.
And the next set is GTA, which oh, that becomes GUA.
And then the last set here is TGA, which becomes UGA.
And you just go back to your handy dandy codon table
and you look each one of those up
and you say, okay, well the first one is AUG.
It's always going to be the first one.
If you're starting from the beginning of the protein.
AUG, whoop, there it is. Methionine, that's the start codon.
Okay, so we have methionine, methionine here.
Then the next one is CGG. Let's go back to that table.
CGG, like the sound effects? (chuckles)
All right, so CGG is arginine. Let's go back.
Hey arginine, so we write an arginine. The next one is UAC.
Let's cut back here UAC, that's tyrosine, Tyrosine.
Then you know the next one is GUA. G, U, A.
That's valine. Yep, valine.
And the last one is UGA. U, G, A.
Oh, there's no amino acid here.
Well that's very true because it is a stop codon.
Remember, stop codon does not actually code
for an amino acid.
It simply tells the ribosome, okay, we're done here.
We stop. We've made the protein and that's what it is.
So your amino acid sequence would read
Methionine, Arginine, Tyrosine, Valine.
That's it. All right, let's summarize what we have so far.
DNA instructs the proper formation of all proteins
without ever leaving the nucleus.
Pretty neat trick, I'd have to say.
Central dogma reads DNA to RNA
to protein, always in that order.
Always, always, always. Transcription is the first stage.
The antisense strand of DNA for a particular gene is copied
into complementary mRNA in the nucleus.
Then that mRNA exits the nucleus
and we start in translation
in which the mRNA reaches ribosomes, which bind
to it and facilitate assembly of amino acids
in the order dictated by the sequence.
Remember, transcription happens
in the nucleus, translation happens
in the cytoplasm or outside of the nucleus.
Ribosomes read mRNA a sequence in sets
of three adjacent bases called codons, starting
with AUG and ending with one
of three different stop codons, UGA, UAA or UAG.
Each codon codes specifically
for 1 of 20 amino acids or a stop codon.
And each amino acid may have multiple codon sequences.
All right, well what's in the next module?
You're asking you ready to go? You ready for more?
I hope so. I really do.
Just know that again, once you get these basics down,
we can start really talking about the applications of this.
And remember, you're going
to have this reinforced again and again and again.
So if you don't 100% get it yet
and not totally comfortable with it, it's okay.
You'll get there. I know you will absolutely get there.
So what's in the next module?
We're going to talk about gene expression
and what that means and as far
as turning genes up down on off DNA replication.
So how does the DNA
in a single fertilized egg end up becoming the DNA
in 50 trillion cells for an adult individual?
How does the DNA replicate itself?
And as part of that, we'll talk about mitosis and meiosis
or the two processes of cell division.
All right, with that, I want to direct you
to a couple of different online resources.
If you're curious about either learning more, seeing it
in a different format, hearing it from someone else other
than me, please, please use any sources
that will be helpful to you.
I'm going to post these on Blackboard site
for you to click through too.
But there's the Genetics Home reference,
which is a great one to click through.
University of Utah Genetic Science Learning Center is
also wonderful.
They have some great videos and some different animations
that might help you to start
to conceptualize what we've been talking about.
And the National Institutes of Health
and Gene Education Center that can also be quite helpful
in just getting a different perspective on the same topics
that we're discussing here.
So with that, I'd like to thank you so much
for your attention and for bearing with me through this.
We will absolutely reach the point
of talking about clinical applications
that is not far away, but hopefully you're starting
to feel a little bit more comfortable
with the terminology, with the concepts of genetics.
You will be amazed, I think, in how much better
and easier it is to start
to understand the clinical applications
of this if you understand the basic science behind it.
All right with that, I will sign off.
So as always, please let me know if you have questions
along the way and I'm more than happy to help
with anything, provide additional resources where I can.
And I will talk with you in the next module. Thank you.