RNA : Adapter Molecule Video Lecture | Biology Class 12 - NEET

hello friends this video on molecular
basis of inheritance part 28 is brought
to you by exam feel calm no more fear
from exam so now the question is who
reads and deceivers the genetic code
because now we got to know that okay
there is something there is a concept of
genetic code based on which we will be
able to tell the sequence of amino acids
and once the sequence of amino acids are
known then the amino acids can be joined
together by peptide bond to form the
polypeptides which will form the
proteins now the question is who will do
this job so somebody actually needs to
read the genetic code and then decipher
the sequence of amino acid so let us
suppose this is the genetic code so
somebody has to read this genetic code
and then give back the result that is
the give then give the result of the
sequence of amino acids so who is going
to do this so this job is done by the
tRNA that is the transfer RNA and that
is why we introduced you to transfer RNA
to squad transfer RNA because it does
the job of carrying the amino acid so it
is going to carry all their minor acids
and it is also capable of reading the
genetic code so by reading the genetic
code it will get to know that which
amino acid it should be and then it
carries that specific amino acid and
helps in the process of protein
synthesis so that is the purpose of tRNA
so let us quickly try to understand the
structure and behavior of tRNA so as you
can see the picture shows how TR and it
looks like so it is transfer RNA these
are nothing but small RNA molecules with
75 to 90 nucleotides so it is like any
other RNA which has a single strand so
this tRNA molecule also is just like any
other RNA molecule which is a single
strand of nucleotides just that it is
comparatively shorter than the normal
are any more strands it has it always
has less than 100 nucleotides so you can
imagine it somewhat
like this a single strand of nucleotides
which is being curved into to form a
shape like this so this is the this was
the traditional shape this was the shape
which was considered traditionally for
the T RNA molecule that is transfer RNA
so what is its purpose it acts as
carriers of amino acids so it helps to
carry the amino acid and then connects
the amino acid to the correct codon on
the MRNA so let us see how what exactly
it does so it plays a very important
role during protein synthesis and how
does it do that
let us have a look at that now let us
suppose that this represents the
sequence on the mRNA and mrna is the one
which is being produced as a result of
transcription from DNA and the sequence
of mRNA is somewhat like this so this is
just an example ok so this is how the
sequences so now based on this sequence
you need to find an amino acid so who is
going to do that that is being done by
the tRNA so what will the tRNA do tRNA
will read this sequence so tRNA will
read it as a GU and corresponding to a
GU whichever is the whichever is the
corresponding amino acid it will try to
bring that amino acid and then connect
it to this so let us suppose if a GU is
for whichever amino acid it will
connected to that again uuu let us
suppose it is for phenylalanine so it
will connect it to the phenyl alanine
again cuu it will see whichever am i
know answered it is so it will connect
it to that amino acid so this this
purpose of connecting or linking the
amino acid with the codon on the MRNA
this job is being done by transfer RNA
so trying tRNA acts as a mediator or a
middle line between mRNAs
winces and the sequence of amino acids
which will later form the proteins so it
can connect the mRNA sequence with amino
acid and that is the main purpose of
tRNA so now let us talk about the
structure of tRNA because the structure
is extremely significant and it is
because of this unique structure tRNA is
able to perform this role so earlier it
was assumed that tRNA has a cloverleaf
structure so this is how a cloverleaf
structure looks like so as I said it is
you can imagine this structure as
something like a straight
strand being curved into to form this
shape so but as for the x-ray
crystallography later the actual
structure was found to be an inverted
l-shape so this is the inverted l-shape
so this is how the structure looked like
when it was observed in Biman the
structure when it was found out by x-ray
crystallography but this is the
traditional cloverleaf leaf structure so
if you look at the structure of the tRNA
closely there are two important parts of
tRNA so let us discuss those two
important parts so one is the anticodon
loop so where do we have the anticodon
loop this portion is the anticodon loop
in fact here and in this structure this
portion which you see here is the
anticodon loop so what is there in this
loop it contains the bases complimentary
to the sequence on mRNA as I said that
the purpose of tRNA is to act as a link
between the mRNA and the proteins so
what will this do is here these three
which you see here these three will be
complementary to
the sequence which is present on the
mRNA so let us suppose if if this is the
mRNA and it has sequences like this so
let us suppose these are the sequences
on the mRNA so what is going to happen
is when a tRNA comes here so the
anticodon part anticodon loop of tRNA
will be this side so the anticodon loop
will have complementary bases when
compared to the basis on mRNA so as a
result they both will tend to come near
each other whereas the other end of the
tRNA will consist of the corresponding
amino acid and this is how it will
connect the correct amino acid to the
right codon and this is how the
connection established
so the anticodon loop will actually
connect to them mrna because of the
complementary base pairing
so no tRNA exists for stop codons but if
there is a stop codon which is
encountered so for that there is no tRNA
that exists initiator tRNA exists for
initiation so for every time you have
that Aug that is one Makonnen so that
acts as the initiator that for that
there will be an initiator tRNA the
other end on the other end we have the
amino acid acceptor end so here you see
this is the amino acid acceptor end or
if you try to look at the inverted L
structure there also you see the same
thing at the site so here you see it
connects to the amino acid so these are
the two ends which are extremely
important because through this end it
connects to mRNA and on the other end it
connects to a mono acid so it acts as a
link between amino acid and the sequence
on mRNA
so here T RNA binds to specific amino
acid
now each tRNA binds to a specific amino
acid so one particular tRNA will have
one amino acid added acceptor end it
cannot have more than one amino acid so
this is how the structure of now please
remember that at least one tRNA has to
exist for one amino acid there can be
multiple tRNAs
sting for one amino acid but at least
one has to be there now tRNA is termed
as an adapter molecule why is it so this
is because of this special property of
tRNA that it can on one hand it can
connect to an amino acid and on the
other side it can also connect to the
mRNA so due to this it is often termed
as the adapter molecule so it is termed
as adapter molecule because it can read
the mRNA sequence on one end and it can
write the amino acid sequence on the
other end so it does a two in one job so
this side is that a minor acid and this
side is done is reading the mRNA so that
is why it is called adapter molecule now
we will see that tRNA play is one of the
most crucial roles during the process of
translation because I hope you are able
to understand now you will be able to
relate it courses that how tRNA plays an
important role in translation because
translation is all about synthesizing
proteins now to synthesize proteins you
need a minor acid the tRNA will help you
to sequence the amino acids you will
know which amino acid should come after
which amino acid depending upon the mRNA
sequence now after that to create
proteins all that is needed is a peptide
bond formation between all the amino
acids and that's all you get
proteins tRNA is called transfer RNA
that is the full form of tRNA why
because it transfers individual amino
acids to the growing polypeptide chain
which later forms proteins as I said
that tRNA will continuously keep on
adding one one amino acid so it is
actually trying to transfer the amino
acid to the polypeptide chain that is
the chain consisting of many peptide
bonds so that chain is going to form
proteins so that is why it is called
transfer RNA so this is how the picture
would be see these are the blue pallet
structures which you see the R these are
the T RNAs and here the red structure is
mRNA so in mRNA you have a particular
sequence now as the tRNA comes it reads
this sequence the complementary
sequences ad
there and the corresponding protein is
present here so it passes on the protein
to this polypeptide chain again this
moves on the next one comes and again
for the corresponding sequence it will
pass on the proteins to this chain again
the next one will come and as I decide
the transfer RNA will keep on
transferring one one amino acid to the
polypeptide chain and that is how the
polypeptide chain will keep on growing
and proteins will be formed so let us
look at some of the examples of tRNA as
an adapter morning let us suppose that
the sequence on M RN a little suppose
this is mRNA and the sequence of bases
on mRNA is something like this
Aug you see you you you so this is the
sequence of bases on mRNA and let us
suppose this is a tRNA
so this tRNA what will be the sequence
of bases on the anticodon end the
sequence of bases on the anticodon end
will be you a c and what should be the
amino acid on this end so the amino acid
for Aug is methionine so this should be
methionine amino acid which is connected
to this end similarly for the amino acid
you AC so this will pass on the beach 1
and then to the polypeptide chain and it
will move on then the next time I know
as the transfer RNA will come into
picture so here the array mRNA is UAC
so what would be the corresponding base
bases on the anticodon loop that would
be a u G and for you a C which is the
corresponding proof and I know a set the
corresponding amino acid is Ty Rosen so
on the amino acid acceptor and tyrosine
will be attached similarly if the next
one is uuu what would be the anticodon
loop sequence it would be a a a and a a
a is for now this uuu is for
phenylalanine so this is going to be fin
and alanine now let us suppose that
after this even if this continues
further let us suppose the after this
the sequence is u G a so this ug a is
for a stop codons of a stop codon will
you do not have T ID in it so there will
be no tRNAs and as a result the
synthesis of the body peptide chain will
stop here so basically in the
polypeptide chain first mature onion
will get added then with peptide bond
Tyros and will get added then again with
another peptide bond phenylalanine get
added and after that it will stop
so no more will get synthesized so this
is how the polypeptide chain formation
will take place so I think we have
partially discussed the process of
translation as well so you can have got
a fair idea about how the process of
translation is going to take place but
however we will discuss translation in
little more detail thank you please
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