Translation RNA to Protein


okay so we wrapped up with transcription
so we’ve already made the RNA copy of DNA it’s we transcribe that gene we
edited it if it was in eukaryotic organism so now that messenger RNA after
it’s been edited we call that piece of RNA a messenger RNA or mRNA now that
mRNA is going to leave the nucleus it’s gonna exit that nucleus and it’s going
to find a ribosome these ribosomes can be free-floating they can be hanging on
as a rough yard regardless it’s gonna find a ribosome and it’s going to then
start the process of translation so that’s our next step in gene expression
of getting that information in a in the DNA in the gene into a protein product
DNA to RNA transcription so RNA to protein is translation so we’re gonna
translate that nucleotide language into the language of amino acids of proteins
so we have some new molecules in here that we need to talk about first okay so
we’re going to introduce more in depth what a ribosome is tRNA and a codon okay
so these ribosomes ribosomes we’ve talked about them before as far as that
they’re the protein factories but what ribosomes are ribosomes are two pieces
of what’s called ribosomal RNA so the ribosomes themselves are actually built
out of RNA and their main job is they’re gonna be the creating a platform for the
RNA transcript to sit on and then it’s going to catalyze the connection of
those amino acids okay so amino acids those are monomers
the building blocks of proteins they’re gonna be connected by the ribosome
acting as a catalyst to bond them together but we gotta get the amino
acids to the ribosome and that’s where this next molecule tRNA or transfer RNA
the T stands for transfer transfer RNA is another molecule built out of RNA out
of a specific type of RNA called T our name and it’s gonna be carrying
amino acids so T RNAs we have 20 amino acids tRNAs are just floating on the
cytoplasm and each tRNA has a specific amino acid
attached to it okay so hanging out there floating around and they’re gonna be
brought into the ribosome with that amino acid and the way that tRNA knows
which amino acid to connect to is it has these three bases right here
so those three little like teeth like things that are sticking down those what
we call an anticodon so those are nucleotide bases ata you season geez
there’s no T in RNA so it’s a you see your gene a three-letter sequence this
anticodon on the tRNA is going to be complementary to the codon on the RNA on
that messenger RNA so if there’s an A in the messenger RNA we would find a U in
the tRNA okay and so the DNA sequence is gonna be read in sets of threes and those
three letters that triplet code that three-letter sequence we call it a codon
so every three letters of the sequence that’s in DNA and then it gets
transcribed into RNA is going to code for the information for one amino acid
so every three DNA and RNA bases codes for one amino acid and it’s a codon
that’s on DNA in mRNA and the anticodon in on tRNA is complementary to the codon
on the mRNA and that’s how that amino acid is going to match up with that mRNA
that anticodon on the tRNA and the codon on the RNA so how is this read so we are
gonna be using a chart like this in class to read the genetic code and this
is really cool we’ve cracked the genetic code we know which codons code for which
proteins from so the way we read this so let’s say we have a transcript that has
a codon that is A C G– A C G that’s our codon ACG on the RNA on the messenger
RNA ACG so what we would figure out what amino acid that would code for is
our first letter A is right here okay our second letter was a
C so we move across this row until we hit C okay so here’s the C column right
here in the third coat our third letter on our codon was a G so ACG that
codes for the amino acid threonine or thr so each of these three letters in
here the prolene serine ser phe these are all shorthands abbreviations for
that amino acid but a couple things that we want to notice here there’s some of
these that are in red these ones up here and this one right down here is in green
so this green codon right here AUG we call this the start codon so AUG is the
start codon what that means is that all RNA transcripts are going to begin with
that AUG codon so it means that all all proteins when they’re being constructed
that first amino acid that’s going to be connected is going to be met methionine
so AUG is our starting codon so all all messenger RNA’s have that first
codon AUG that’s where the starting the beginning of translation occurs and then
the rest of the codons in that transcript are gonna be any combination
of any of these other amino acids and then the way that the ribosome knows to
stop translation is if it hits one of these stop codons so these ones in red
these are the stop codon so UAA UAG and UGA those are three codons that do not
have a matching tRNA there is no complimentary anticodon or the tRNA that
will match up with the stop codons and so at that point the RNA would just it
would dissociate from the ribosome and then translation would stop so these
stop codons indicate that this is the end of the process of translation okay
and we’ll practice this a little bit later on so how this works is first
thing that’s gonna happen that mRNA that messenger RNA is going to associate with
the smaller piece of that ribosome so I kind of think like ribosomes look like
weird hamburger buns so we’re gonna have the lower button of the ribosome the smaller subunit of the ribosome is gonna connect it to that RNA
the RNA is gonna sit right on top of it and then our first tRNA is carrying that
start amino acid that methionine that AUG codon that start codon that
Methionine and carrying tRNA is going to land
oh and that anticodon on the tRNA is gonna match up with the codon of that
start codon on the MRNA okay so that’s how everything starts so once those
pieces are in there the lower bun the smaller right ribosomal subunit the mRNA
sitting right on top of it and then the a the methionine
tRNA okay so that’s how we begin translation once all those pieces are
set up these larger ribosomal subunit the top bun if you will it’s gonna
come in it’s gonna connect as well okay so this larger ribosomal subunit it’s
gonna come in and what this is really doing this is where the catalysis
happens so this larger ribosome subunit what it’s going to be doing is as new
tRNAs come in that are charged up with their amino acid so this anticodon right
here AAA this matches up with the codon UUU on
this piece of mRNA and that is the anticodon that’s carrying phenyl alanine
phe right there okay so what the ribosome what the larger ribosomal subunit does is it takes those two amino acids and it forces them to
bond kind of like an enzyme it’s a catalyst so it’s gonna catalyze the
connection of those two amino acids together and it’s going to create a
peptide bond so that’s the bond between amino acids we call that a peptide bond
and so once it starts to connect those amino acids it creates a polypeptide
chain and so that polypeptide chain is the first step in the building of that
protein so it’s going to connect those two amino acids together so the
methionine gets connected to this phenyl alanine right here it’s gonna be
attached onto that phenyl alanine it’s gonna grow out of that phenyl alanine
just like we see here then it’s gonna move over it’s gonna move over this
original tRNA that was carrying methionine it exits it leaves it’s gonna go
get charged up with another methionine then once it moves over one codon it
exposes the next codon right here okay so the CGA codon it’s going to match up
with the anticodon GCU and this tRNA that’s carrying that anticodon GCU is carrying
the arginine amino acid and guess what it’s gonna have the same thing happened that
phenyl alanine right here it’s again the ribosomes gonna catalyze the bond
between that phenyl alanine then that arginine it’s gonna create a peptide
bond between those two amino acids and now our polypeptide it’s gonna be three
amino acids long okay and so it’s gonna keep doing this process of connecting
these amino acids and moving over one codon connecting connecting connecting
moving move and moving until it hits one of the stop codons and then everything
dissociates that polypeptide chain floats away it’s gonna get fold it up
into its final protein shape maybe connected with some other proteins and
then that mRNA reused those tRNAs get charged back up again and then that
protein could get made again or that ribosome could find another mRNA and make a
different protein okay so all these pieces can be recycled and our
mRNAs will get degraded over a certain period of time depending on the organism
it can be 20 minutes it can be a couple weeks it just it varies so this mRNAs
can be reused or they can be degraded the tRNAs are recharged up the ribosome
gets reused and it can go through this process again and again okay so let’s
practice so let’s say we have a DNA sequence right here I want you to pause
the video real quick and I want you to see what is the complimentary DNA
sequence I want you write that down don’t forget your three prime in your
five prime ends how would you translate how do you transcribe this DNA sequence
transcribe this scene a sequence right here up top into an mRNA okay so
transcribe this DNA into an mRNA and then that mRNA that you create translate
that into protein using this chart right here okay so go ahead and pause all right so hopefully you paused and
got all of that done so here we go so if we were to find the complementary
sequence of this DNA strand here’s what it’d be right here so A match with T
G match with C and notice the five Prime and the three prime end so in
this end we have the three prime because DNA is anti parallel we would find the
five prime end over here so they’re running opposite directions from each
other okay now if we’re gonna transcribe this DNA sequence up here into RNA
here’s what we would have and I broke this up into three so this is gonna be
helpful for you also is a view as you’re transcribing break up into three so you
see these dashes just indicate separations between codons so UAC — CGU this is what we have when we convert this DNA strand when we transcribe this
DNA strand into RNA notice again here’s our five prime end
because it’s gonna be also be anti parallel to original DNA strand which is
running on three prime on this end okay let’s now if we translate this translate
this into protein into amino acid our first codon UAC so let’s find
that here we go so here’s our first letter on this side U go over to our
second letter A and then our third letter C so this would be the amino
acid tyrosine tyr okay our second codon CGU our first letters in that codon is C our second letter is a G and our third letters a U so arginine Arg
right there okay so that we are their second amino acid ACG right here this
codon right here A is our first letter over to C and there’s their
letters a G. ACG thr that’s threonine okay so our next amino acid GGC is
our next codon so G’s our first letter G is also our second letter and then C is
our third letter so GGC right here is the amino acid glycine
okay so gly and then we have also UAC again UAC we had at the beginning that’s tyrosine so UAC alright and so
that’s how we transcribe and translate a gene into its final protein product this
is how genes are expressed this is how we turn genes in our bodies and do
things like our proteins like your hair or your nails our enzymes in our body
everything transcription DNA to RNA and then translation RNA to protein at the
ribosomes alright good job

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