Packaging of DNA Helix Video Lecture - NEET

did you know that the length of a DNA or
deoxyribonucleic acid double helix in a
typical mammalian cell is about 2.2
meters
this length is obtained by multiplying
the total number of base pairs present
in the DNA double helix with the
distance between two consecutive base
pairs
a number of bass players present in a
DNA double helix in a typical mammalian
cell is 6.6 multiplied by 10 raised to
the power 9 and
stands between two consecutive base
pairs is 0.34 nanometers or 0.3 4
multiplied by 10 raised to the power
minus 9 meters by multiplying these two
factors we get the length of the DNA
double helix as 2.2 meters
have you wondered how such
polymerase
packaged within a typical nucleus
engine of about 10 raised to the power
minus 6 meters
to understand this
packaging of a DNA double helix which is
different for both prokaryotes and
eukaryotes
in prokaryotes such as eco life
the nucleus is not very well defined
however the negatively charged DNA is
not scattered throughout the cell but is
arranged in large loops
is held together by a few positively
charged proteins in a region known as
the nucleoid on the other hand in
eukaryotes the manner in which a DNA
double helix is packaged within the cell
is more complex
eukaryotes contain a single molecule of
negatively charged DNA packaged around a
spoon of positively charged basic
proteins known as histones
the charge in a protein is decided by
the abundance of amino acid residues
with charged side chains
this case the proteins are positively
charged as the histones are rich in
basic amino acid residues like license
and arginines
which carry positive charges in their
side chains
furthermore the histones are arranged to
form a unit of eight molecules known as
the histone octamer
now around the positively-charged
October
a charged DNA molecule is wrapped to
form a structure known as the nuclear
zone
which is held in place by the h1 histone
nucleosome has around 200 base pairs of
DNA helix and
the nucleosomes present in chromatin can
be seen as a beads on string structure
will observed under an electron
microscope
it is the nucleosomes that make up the
repeating unit in chromatin
the thread-like bodies present in
nucleus
the chromatin fibers are of two types
chromatin and
the chromatin
in a typical nucleus euchromatin fibers
of 30 to 80 nanometers in diameter are
loosely packed and stained light
on the other hand
cotton fibers of about 300 nanometers in
diameter are more densely packed and
stained dark
moreover of the two types of chromatin
fibers you chromatin is
transcriptionally active while
heterochromatin is inactive
these chromatin fibers coil further and
condense to form short and thick bodies
called chromosomes during the metaphase
stage of cell division
in this way
DNA double helix is packaged into a
chromosome which is further packaged
within the nucleus
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you