Mitosis Prophase, Metaphase - cell cycle and cell division, Biology, Class 11 Video Lecture

hello friends this video on cell cycle
and cell division part 7 is brought to
you by exam feel calm no more fear from
exam so let us talk about profiles that
is the first step of mitosis so what
happens here the chromatin threads
condense to form chromosomes now this
was the nucleus which we had so far like
after the interface in interphase what
happened these were the chromatin trade
threads which got replicated that is why
you have one in red color the other one
is blue color just to distinguish that
okay one is the replicated one so the
chromatic threads got replicated the
centrioles got replicated and this is
the status of them sale as of now now
here in this phase what happens the
chromatic threads condense to form
chromosomes so what do we mean by
condense and I now the threads are
something like this now if these threads
condensed together that means they
become compact they arrange themselves
something like this in this pattern and
this pattern is known as chromosomes and
the center at which they are connected
to each other that is known as
centromere I have explained all these
things in the previous cell in one of
our previous lessons so I am sure you
all know about all these things so in
this case chromosomes are formed so
something like this so here you can see
the thread like structures are gradually
getting arranged so they are like
getting compact and gradually it forms a
structure like this and the central part
as long as centromere and each of these
chromosomes so basically there are two
chromosomes which get connected at the
centromere so each of this chromosome is
known as a sister chromatid
because now we will be using beads
terminal lodges where you of attend I
have already discussed about this before
so this will in turn what will happen
now the side to side
this assembles what is cytoskeleton the
skeleton skeletal framework of the cell
that the cytoskeleton what is it made a
pocket is made up of microfilaments and
microtubules I am sure remember all
these days when you spoke about the
lesson on cell if not please review it
so here the cytoskeleton dis assembles
so no cytoskeleton is there so what will
happen to those microtubules and
microfilaments we will see they will get
utilized in some other way
so the sections migrate to opposite
poles and form a bridge of microtubules
called spindle apparatus this is very
very important this step is very
important so you saw here that the
sensual are duplicated now gradually
what will happen is the centrioles will
migrate to opposite poles let us suppose
this is one century on the other central
will migrate here so the bold essentials
will migrate to opposite poles and as I
said the chromatic threads have
organized into chromosomes now the
cytoskeleton has disassembled by those
microtubules will now be utilized to
form thread-like structures in this
fashion which is known as spindle fibers
why is it called spindle fibers because
of its shape it is known as spindle
fibers so structure like this will arise
from the two centrioles which is there
on the opposite poles so this will
happen so you got my point the
cytoskeleton will disassemble so what
will happen to the microtubules of the
cytoskeleton the same thing will form a
bridge like structure from the two
centers or opposite poles and this is
where as spindle apparatus now
chromosomes attach two spindle apparatus
by kind NATO code so what is a NATO core
now in the structure of chromosome as I
said the same two structures for
centromere now over the centromere you
have some hook like structures which are
known as
of course basically about books but it
act like hooks so what happens is these
each of this chromosomes will get
attached to these spindle fibers at
their kind mental course
so Kyle otoko's will act like who so
that it can attach it attached to the
spring duel fibers so these are some of
the changes which will take places
prophase so a lot of things will happen
in prophase firstly chromatic threads
will form condense to form chromosomes
cytoskeleton in this example and the
same microtubules will form bridge like
structures but spindle apparatus
chromosomes will attach to the spindle
apparatus by cognitive force nuclear
envelope start breaking down so if you
see here at this place you had a
complete nuclear envelope gradually it
start breaking down and finally it
vanishes so the nuclear envelope will
also break down now when you talk about
all these things like kind into poles or
the microtubules they are all beautiful
proteins so protein is there everywhere
so now you understand why we say that
before the process of sending fusion
start the cell should be very well
prepared for the diffusion to take place
and that is why protein synthesis take
place in the g2 phase that is the second
lab fees so now what happens in the next
step that is the better phase so in this
phase the nuclear membrane completely
disappears so there in started breaking
now and now it is completely gone
chromosomes assemble at the equator this
is again very very important so you saw
the chromosomes there they are attached
to the spindle fibers and then kind into
four so this white color structure which
you see here that is nothing but kind
Interphone
and these are the spindle fibers so
these are the spindle fibers so here in
this picture you can actually see how it
gives the shape of a spindle so it
attaches to the
now because of the force inserted by
both the centrosomes and also by these
fibers what happens is this chromosomes
are gradually arranged to act that
equator of the cell and this is known as
a metaphase plate because it looks like
a plate at the equator and that is why
it is termed as metaphase plate so now
another special thing which should be
noted here is that if you see this
alignment has a special feature so now
here everywhere you see 1 2 chromosomes
right so what are these this is 1 this
is 2 so they are basically same two
copies of the same chromosome so now
these two copies of chromosome are these
two sister chromatids are arranged in
such a way that one sister chromatid is
connected to the spindle fiber of one
central whereas the other sister
chromatid is connected to the spindle
fiber of the other sensor so this
spindle fiber is towards this side and
this module 5 and this chromatic is
towards this side so that is the
strategy this is how it should be
arranged at the equator now how it gets
erased at the equator that happens due
to the counter forces between the
microtubules and the kind H of course
that happens because of the forces
between there and that is right here you
can see the centrioles were not exactly
or opposite poles but when they are
exactly opposite to each other they make
sure that the alignment is in this
fashion and formation of metaphase plate
tape occurs now why are the chromosomes
arranged in this fashion so that when
both of them are pushed towards opposite
poles one chromosome will go this side
and one throw magnet will go this side
the other sister chromatid will go this
side so that the two sister chromatids
can get separated now the question is
why do we want them to separate we will
see that in the next phase thank you
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