Gene Expression Simplified – General Biology – Transcription & Translation – Protein Synthesis


hi everyone it’s dr. Jory this video is
designed for students in general biology who are studying gene expression the
central dogma I cover the three steps of transcription and translation if you
like the video please SMASH that like button, subscribe to the channel and
enjoy! How did the RNApolymerase know where to go? The promoter. So the promoter
is like at a nightclub think come on into the club so let’s say it’s right
here promoter signals RNA polymerase start
here because we have the gene we want right there and the RNA polymerase does
two things what does it do unwinds the DNA strand by breaking hydrogen bonds
between nitrogenous bases and what else does it do it’s a two-in-one enzyme it does complimentary nitrogenous base
pairings so if we have here let’s say there is G C G but on the RNA transcript
there will be what C G C what is this part of the DNA called template strand
so you’re using the template strand to build your RNA transcript where is this
all taking place inside the nucleus well this is your RNA transcript this part
has already been built so it’s going in this direction what is the part of the
DNA called in which you’re building your transcript from the gene right the gene
is right after the promoter so this let’s say from this area is the gene and the gene is like the recipe it’s got
all the instructions on how to build how the protein that you’re gonna
make okay so where are we here we’re in the nucleus if we’re in a eukaryotic
cell what if we’re in a prokaryotic cell it would take place in the cytoplasm so
this is called the central dogma it’s the go from DNA to messenger RNA to
protein the central dogma what is the process call to go from DNA to mRNA transcription and to go from mRNA
protein translation in the nation there’s three steps of transcription
there’s also three steps to translation they’re both the same they’re not the
same steps but they’re called the same so what are they step 1 initiation 2 elongation three termination so initiation we already started over
here that’s the promoter there is something
that’s right before the promoter tada the tata box so it would be like right
before here so scientists when they’re sequencing a genome they can look for
this type of coding in the DNA and that gives them the signal that here comes a
gene once you see the tata then you know a promoter is coming up and then that’s
going to be the gene right after that now what tells it to stop the terminator
so the terminator say it’s right here Terminator says that’s it
so initiation promoter says RNA polymerase start here start building
your mRNA transcript an mRNA transcript is like a photocopy of the gene that’s
why we call it a transcript the second stage is elongation RNA polymerase
complementary base pairing building your mRNA transcript that should have had an
M on there mrna transfer an elongation you have the mRNA transcript getting
longer it tells you right in the word what it’s doing make it longer once you
reach the end of the gene you hit the terminator
termination you’re all done at that point the DNA double helix will go back
to the way it was the hydrogen bonds between the nitrogenous bases they will
bond the same and then your mRNA transcript it’s known as immature at
this point all right now that you’ve finished building your mRNA transcript
you have it here it’s known as immature there’s something that you have to do
next it’s called processing and what do we do
for processing there’s about three different things we do right and you all
just set it at the same time so first thing well actually I don’t even know if
this is the first thing but one of the things we do is we put on a cap a
guanine cap and a poly a tail so the poly a just means it has a bunch of
adenine poly a tail why do we put that on put up your hand good so it protects it from enzymes
because it’s gonna go through the nuclear pore gonna come out here into
the cytoplasm and we have our n aces they’re also known as exonucleases that
could chop that up so now we’ve got protection we have the squatting cap
poly a tail we also have regions of the transcript some are coding and some are
non-coding so we call the ones that are coding regions we call those exons and
we call the ones that are non-coding we call those introns which ones do we want
to keep before we send it out into the cytoplasm we wanted to export the exons
so e equals exons and introns are the non-coding ones so those are the ones we
are going to splice it’s called RNA splicing so we’re gonna chop those out
we’ll keep the exons we’re gonna export the exons and another way to remember
that is then we’re gonna express the exons for gene expression so then your
transcript is now mature so we can leave you got rid of all the introns you only
have the exons now those are the coding regions and then of course you have your
cap and you’re probably a tail and now transcription complete then we can get
into translation so now we have finished transcription
that took place in the nucleus we made our mRNA transcript we have processed
our mRNA transcript it’s now mature we chopped out the introns kept the exons
put the poly a tail on put the cap on exported it through the nuclear pore
it’s now in the cytoplasm it’s likely going to be in white organelle right now yes the rough endoplasmic reticulum
which is a continuous and do–make membranous system with the nuclear
envelope so we’re probably in the rough endoplasmic reticulum now we could just
be in the cytoplasm though when we meet up with a ribosome so the ribosome it’s
going to start it has two subunits small and large obviously this isn’t to scale
this ribosome is ginormous it’s going to be a lot smaller than them
but for illustration purposes let’s do it like that
so we’ve got a large subunit here now let’s go back to translation translation
we will just translate the message the messenger RNA we want to translate that
into what into a protein so we want to decipher the genetic code and that will
allow us to build our polypeptide which will become a protein translation as we
talked about earlier has three steps initiation elongation the same steps that
transcription that and what’s the last one
termination so initiation is basically start so start we’re gonna have certain
it’s always hard to draw this I don’t really have enough space but the mRNA
codons these are going to be codons to get things started
you have three nucleotide bases those are going to be a u G to get things
started so start is a u G and that codes for
what amino acids put up your hand finding your voice a lot deeper than I
remember so the thiamine is what all polypeptides will start with and that
does require energy that something to consider is that the large subunit has
three sites these sites are going to be where the transfer RNA fits in the three
sites are called the exit site the polypeptide site and the amino acid site
I like to remember our Environmental Protection Agency because I care about
the environment you could also spell it eight backwards
the beauty of this is that the name those sites tell you exactly what they
do in the exit site that will be where the transfer RNA has already got rid of
its amino acid and it will leave from there in the polypeptide site that will
be where you see the growing polypeptide chain so at this point because you just
started there’s only gonna be one amino acid on there and that amino acid is
gonna be fine now the next amino acid is gonna come
down into the amino acid site so let’s say the next amino acid I’m gonna throw
a codon at you tell me what the amino acid is so let’s say the next codon is G
a G so it’s going to be a triplet code it’s gonna be G a G gag what is the
amino acid for that who’s got unfortunately I don’t have them all
memorized there’s 61 use your mRNA codon chart and that’s gonna tell you which
amino acid is being pulled down next okay the codons that I’ve drawn here
it’s not exactly accurate because there should be another triplet here so in
total there would be nine nucleotides but anyway what will then happen is the
ribosome it’s like a car driving along the mRNA highway or mRNA Road so it’s
gonna continue driving along and each time you will have this is going to
shift over to that so now it’s gonna have two amino acids because the
polypeptide one transferred then it’s gonna go to the exit site it’s going to
leave everything’s gonna shift over this one that eyes – it’s gonna go over to
the polypeptide site then a new tRNA that’s sitting out in the cytoplasm
holding on to the next amino acid it’s gonna get called down and everything
shifts over that keeps happening it happens super quick and you know once
the dust settles and you read the entire mRNA transcript that’s the whole
elongation phase elongation tells you again exactly what it does you’re just
making it longer you’re adding all those amino acids to it and that also requires
energy so make it longer and that requires energy
so polypeptides can range in size they could be 30 amino acids long they could
be 3,000 amino acids long just depend alright moving on so let’s say we
finally lined up all the amino acids and they have to be in the exact order that
the recipe calls for the transcript is like photocopy of the recipe
okay the gene is the recipe the DNA is like this giant recipe book so you have
your specific recipe cook your protein and then eventually
you’re gonna come up on let’s say it’s at the end here you will hit a codon and
it could be one of three different ones so it could be you are great you are
awesome or you got it all those are all known as do it in red stop codons it
tells you right in the word what happens termination it stops stop you’re done
now is there we didn’t talk with this in this video yet the tRNAs they have
what’s called anticodons so they have one two three one two three one two
three those are complementary to the mRNA codons okay now once you hit one of
these three stop codons is there an amino acid that goes with that no what
does this tell you stop but what is it what is it calling for release factors
good release factor is an enzyme whoops release enzyme release factor enzyme and
what that does is hydrolyze so with the addition of water it breaks a bond hydrolyze the bond between the
polypeptide so you have your big polypeptide here
let’s get a little messy now between the polypeptide and the last teeth RNA once
that release factor comes in it’s like scissors so it snips snips the bond from
the tRNA to the polypeptide breaks it apart and that signals for everything to
disassemble the large subunit falls away the small subunit falls away you’re
going to recycle your ribosome your mRNA is probably going to get just recycled
and you are complete you translated your message into a polypeptide at that point
your polypeptide is gonna look something like this what does that look like a neck lace
that’s right neck lace not necklace if your necklace means don’t have a
necklace what do you call this do you call it a sugarless or do you call it a
shoelace shoelace that’s right so why would you call out a necklace all right
sorry the neck lace it’s not necklace anyway here we go there is your primary polypeptide so what we’re talking now
about is protein structure this is the first level of protein structure primary
polypeptide some ammeter some polypeptides might be happy at this
level most will go on to the secondary structure which is like an alpha helix
or a beta pleated sheet some of them will go on to the tertiary
structure which is now more three-dimensional and then some will
wonned to the quick ternary which is two or more tertiaries bonding together like
EEMA globin for instance it’s messy it’s not enough speed that’s the hardest
thing about this there’s just not enough space to get it all in there as the
polypeptide is moving outwards in the cytoplasm through the rough endoplasmic
reticulum then it’s going to break off from vesicle attached to the rough
endoplasmic reticulum it’s going to travel over to the Golgi apparatus which
is known as the post office shipping receiving packaging that is where it
will reach its final shape whether it’s secondary tertiary quaternary is the
fourth one from there it’s either going to butt off into another vesicle stay
within the cell if it’s needed there or you’re gonna export it it’s gonna leave
the cell through the plasma membrane and head to wherever it’s supposed to go
that is called gene expression the whole process called gene expression we also
call it central dogma and it includes transcription and translation we’ll
watch up anything else

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