-
-
ARMANDO HASUDUNGAN:
Armando Hasudungan Biology
-
and Medicine videos.
-
Please make sure to subscribe,
join the forum and group
-
for the latest videos.
-
Please visit Facebook
Armando Hasudungan.
-
-
Now, in this video, we will look
at an overview of transcription
-
and translation in cells.
-
It won't go into a
whole lot of detail,
-
but just so we get an
idea of what is happening.
-
So we begin by
going inside a cell.
-
Here is the membrane of
the nucleus, not the plasma
-
membrane but the nucleus, where
our genetic material is stored.
-
And outside this
nuclear membrane
-
is the cytoplasm, which is
the fluid within the cell.
-
Now, within the cytoplasm,
we find many things,
-
including amino acids.
-
And there are many
types of amino acids.
-
There are 20 in total.
-
Now, going back
inside the nucleus,
-
we can find our
genetic material,
-
which are packaged
up into chromosomes,
-
forming chromosomes.
-
We have 46 chromosomes in total,
23 pairs, one from each parent.
-
-
If we unpack this
particular chromosome,
-
the genetic material is cleverly
wrapped around these proteins
-
called histones.
-
So pulling out some
of these histones,
-
our genetic material
here are organized,
-
wrapped around these
individual histones.
-
Our genetic material is
called DNA, or, long,
-
deoxyribonucleic acid.
-
If we unwind the DNA, we can see
that the DNA is double stranded
-
and is made up of nucleotides.
-
There are four
types of nucleotides
-
which make up the DNA.
-
-
So what do we do with this DNA?
-
Well, we can replicate
it, and we do so
-
during cell division
called mitosis.
-
And I have a video on that if
you want to watch it, here.
-
-
Our DNA also
contains many genes.
-
Genes are regions in the DNA
that do things for our body.
-
For example, genes
make templates
-
for proteins and enzymes.
-
To make proteins and
enzymes for our body,
-
first, the DNA has to make RNA.
-
RNA stands for ribonucleic acid.
-
Our body makes RNA through the
help of an enzyme called RNA
-
polymerase.
-
Now, RNA polymerase
synthesizes an RNA
-
using one of the DNA
strands as a template.
-
This process of
synthesizing RNA from DNA
-
is called transcription
because we are transcribing.
-
-
RNA typically has a
poly-A tail, which
-
means it has many adenosine
nucleotide at one end.
-
And on the other
end, there is a cap,
-
and we'll talk about
these features later on.
-
This particular RNA
that was synthesized
-
by the RNA polymerase
is a messenger RNA,
-
or mRNA for short.
-
It is a pre-mRNA,
to be specific,
-
because it has not been
properly converted to a mRNA.
-
There are actually three
major types of RNA in humans.
-
These are the messenger RNA,
mRNA, transfer RNA, tRNA,
-
and ribosome RNA, rRNA.
-
And they are all synthesized
by different types
-
of RNA polymerases.
-
You have RNA polymerase
I, II, and III.
-
But we don't have to
worry about that now.
-
Anyways, let's go back to the
pre-mRNA that was just made.
-
So now we are focusing
on messenger RNA.
-
The pre-messenger RNA,
like all pre-RNAs,
-
are made up of
nucleotides as well.
-
They also contain regions
called introns and exons.
-
The pre-mRNA then undergoes
a process known as splicing.
-
Splicing is basically when
the regions, called introns,
-
are removed from the pre-mRNA.
-
But the exons, they will stay.
-
-
And this will form a
unique type of mRNA
-
and therefore a unique
type of protein.
-
So after splicing, after
introns are removed,
-
this will form an mRNA,
still with the poly-A tail
-
at one end and a
cap at the other.
-
Now, the mRNA will
then leave the nucleus
-
through the nuclear pore
and into the cell cytoplasm.
-
-
So we know that the
mRNA has something
-
to do with making proteins.
-
What does it actually do?
-
Well, the mRNA serves as a
template to form proteins.
-
mRNA is sort of
like a foreign book
-
that has to be translated
to make proteins,
-
if that made any sense.
-
Now, let's just pause there
with the mRNA and look
-
at the other RNAs
because they are
-
they are important
as they participate
-
in protein synthesis.
-
So let's go back to the
nucleus, to the DNA again.
-
A specific type
of RNA polymerase
-
can synthesize pre-tRNA,
pre-transfer RNA,
-
through the process
called transcription.
-
The pre-tRNA is then spliced,
removing the introns,
-
and then you get a type of tRNA.
-
The tRNA will then leave the
nucleus to the nuclear pore
-
into the cytoplasm.
-
The tRNA will actually
fold up into a shape
-
that looks sort of like this.
-
So what do we do
with these tRNAs?
-
Or what do the tRNAs do?
-
Well, remember that tRNA is
made up of nucleotides, not
-
amino acids.
-
And what tRNA actually do
is that every tRNA will
-
attach to one amino acid.
-
Remember, in the cytoplasm,
there are amino acids.
-
-
See, in the cytoplasm,
there is this enzyme called
-
aminoacyl tRNA synthetase.
-
Aminoacyl tRNA
synthetase essentially
-
attaches an amino
acid to a tRNA,
-
forming a tRNA
with an amino acid.
-
-
So now what we have
in the cytoplasm
-
is tRNA with different
types of amino acids.
-
Then we have an mRNA, which
is a template for the tRNA
-
with the amino acid.
-
So what is missing?
-
Well, the only thing
that is missing
-
is an enzyme that
actually connects the two,
-
connects the tRNA with the mRNA.
-
This enzyme is
called a ribosome,
-
and a ribosome is made from
rRNA, our last type of RNA.
-
So let's go back to
the nucleus and see
-
how we form this ribosome.
-
But before that, please remember
that all these RNA, tRNA, mRNA,
-
they are all RNAs.
-
They are all made up of
nucleotides, not amino acids.
-
-
So we are back in the
nucleus to form ribosomes.
-
We actually have to dig
deeper into the nucleus,
-
a region called the nucleolus.
-
Our DNA in the nucleolus
have genes to make ribosomes.
-
A special RNA polymerase
called RNA polymerase
-
I will synthesize
rRNA, ribosome RNA.
-
-
And if I have not
mentioned earlier,
-
the RNA polymerase
that synthesizes tRNA
-
is RNA polymerase III.
-
Anyways, let's go
back to the nucleolus.
-
RNA polymerase I will synthesize
pre-rRNA, pre-ribosome RNA,
-
which will be spliced to
form two rRNA strands.
-
One is small, and
the other one is big.
-
The small and the
big rRNA strands
-
will eventually form the
small and large subunit
-
of the ribosome.
-
These strands will then
leave the nucleolus,
-
where they will fold to form
a small and large subunit
-
of the ribosome.
-
The subunits are still termed
pre-ribosome in the nucleus.
-
The pre-ribosome can then leave
the nucleus into the cytoplasm.
-
Within the cytoplasm, the
small and large subunit
-
will attach to the cap
end of the mRNA, like so.
-
So here we have a
functioning ribosome
-
with its large and
small subunit attaching
-
to the cap region of the mRNA.
-
-
The ribosome has
three special sites
-
within it, the E, P, A site.
-
Now, each of these
mean something.
-
But just for simplicity,
you can think
-
of A as attachment, E as exit.
-
So anyways, the ribosome will
move towards the poly-end
-
of the mRNA like so.
-
During its movement,
the ribosome
-
will act like a factory
for protein synthesis.
-
It will attach tRNA
with mRNA, essentially.
-
Remember, the tRNA is
made up of nucleotides,
-
so all these are nucleotides.
-
Three nucleotides down
this end of the tRNA
-
is special because it is
what will bind to three
-
nucleotides on the mRNA.
-
These three nucleotides
are called codons
-
in mRNA and anticodons in tRNA.
-
So, for example, if
this tRNA anticodon
-
matches this codon
of the mRNA, it
-
will bind on the A
site of the ribosome.
-
The ribosome will
then keep moving,
-
and then the tRNA will then be
on the P site of the ribosome.
-
The ribosome will
release the amino acid
-
from the tRNA in the P site.
-
And then as the
ribosome keeps moving,
-
the tRNA then will exit
through the E site.
-
The amino acid that was
released from the tRNA
-
will join with other amino
acids from other tRNAs
-
to form a polypeptide
or protein.
-
Now, this whole process
is known as translation.
-
-
So what the ribosomes
are doing is
-
that the ribosomes are
translating the mRNA
-
to make proteins.
-
Now, just for your
interest, this protein
-
that is just synthesized by the
ribosome or any other proteins
-
for that matter can be broken
down into amino acids again,
-
and then the cycle can continue.
-
What is important
to understand here
-
is that amino acids,
tRNA, mRNA, and rRNA
-
are critical in
synthesizing proteins.
-
Also, many enzymes in our
body are made up of proteins.
-
They're proteins.
-
However, a ribosome is not
made up of amino acids.
-
It is made up of nucleotides.
-
Quite unique.
-
Thank you for watching.
-
Hope you enjoyed
this short overview
-
on translation
and transcription.
-
Bye.
-