Chromosome structure, types and composition | NMDCAT 2021

About This Video
Chromosomes are thread like structures that appear inside the nucleus at the time of cell division.
They were irst observed by the German embryologist Walther Fleming in 1882, when he was
examining the rapidly dividing cells of salamander larvae. Since their discovery, chromosomes have
been found in the cells of all eukaryotes. Their number however varies from species to species.
Pencillium, a fungus, has only one pair of chromosomes, while some ferns have more than 500 pairs.
A mosquito has 6, honeybee 32, corn 20, sugarcane 80, frog 26 and a mouse has 40 chromosomes.
Human cells have 46 chromosomes, consisting of 23 pairs. Each of these 46 chromosomes
contains hundreds or thousands of genes that play important roles in determining how a person’s
body develops and functions. The possession of all these chromosomes is therefore, essential
for survival. Missing of a part or whole of chromosome leads to serious consequences, and death
TYPES OF CHROMOSOMES
Typically, a chromosome is made of chromatids, centromere, (primary constriction),
Chromosomes may widely difer in appearance. They vary in size, staining properties,
the location of centromere, relative length of two arms on either side of centromere,
and the position of constricted regions along the arms. The particular array of
chromosomes that an individual possesses is called its karyotype . Karyotypes
show marked diferences among species and sometimes even among individuals of
the same species.
The chromosomes are called telocentric, acrocentric, sub metacentric and metacentric
depending upon the location of centromere between the middle and tip of the
chromosomes.These chromosomes- acquire diferent shapes at the time of anaphase during cell
division. The usual shapes are i, j and v.
COMPOSITION OF CHROMOSOME
Chromosomes are composed of DNA and protein. Most are about 40% DNA and 60%
protein. A signiicant amount of RNA is also associated with chromosomes, because
these are the sites of RNA synthesis. The DNA of a chromosome is one very long, double
stranded iber that extends unbroken through the entire length of the chromosome.
A typical human chromosome contains about 140 million (1.4 x 108) nucleotides in
its DNA. The amount of information, one chromosome contains would ill about 280
printed books of 1000 pages each, if each nucleotide corresponds to a word and each
page had about 500 words on it. Further more, if the strand of DNA from a single
chromosome were laid out in a straight line, it would be about 5 centimeter long.
Fitting such a strand into a small space of nucleus is nature’s marvel - and that’s only 1
of 46 chromosomes. In the cell, however, the DNA is coiled allowing it to it into a much
smaller space than would otherwise be possible.
How can this long DNA ibre coil so tightly? If we gently disrupt a eukaryotic nucleus
and examine the DNA with an electron microscope, we ind that it resembles a string
of beads. Every 200 nucleotides, the DNA duplex is coiled around a core
of eight histone proteins forming a complex known as a nucleosome. Unlike most
proteins, which have an overall negative charge, histones are positively charged due
to an abundance of the basic amino acids arginine and lysine. They are thus strongly
attracted to the negatively charged phosphate groups of the DNA. The histone cores
thus act as magnetic forms that promote and guide the coiling of the DNA. Further
coiling occurs when the string of nucleosomes wraps up into higher order coils called
supercoils.
Highly condensed portions of the chromatin are called heterochromatin. Some of
these portions remain permanently condensed, so that their DNA is never expressed.
The remainder of the chromosome called euchromatin is condensed only during cell
division,when compact packaging facilitates the movement of the chromosomes. At all other
times, euchromatin is present in an open coniguration and its genes can be 125
expressed. The way, chromatin is packaged when the cell is not dividing is not well
understood beyond the level of nucleosomes and is a topic of intensive research.

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[@Scholarly_Safari]

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[@letssimplifylife2828]

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[@NZ-yk1lc]

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[@abidabidghafoor8002]

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[@faisaliqbal8087]

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[@zubii_creation]

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[@abeersualeh6110]

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[@biologyflavour5512]

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[@yasinmashory4182]

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[@biologyflavour5512]

Awesome ...

[@azamazeem]

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[@minahil.ayesha]

sir i m amazed

[@al-khairi7865]

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[@maleehaazizaziz849]

Superb Sir g it helped me a lot many many thanks 😊

[@sumeshs8743]

Sir histones are H1, H2A,H2B, H3 & H4

[@fatimamughal3986]

Okay sir done

[@sabahameed5974]

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[@sabahameed5974]

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[@Scholarly_Safari]

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[@sehar2938]

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[@abidabidghafoor8002]

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[@ammarashafiq326]

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[@mominasaeed5296]

Mahnoor Saeed done ✔️

[@nishashehzadi1953]

nice😎😎

[@hafizasadiakanwal3705]

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[@amalart9345]

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[@rohabshakil7223]

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[@areebanoor2050]

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[@khan-kz8fc]

Junk DNA q useless hota hain ?

[@kinzahafeez5504]

Done✅

[@zonishah3044]

Sir tRNA and rRNA synthesis from setllite DNA...how this part have useless sequance😑😑

[@U_life_with_us]

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[@khan-kz8fc]

السلام علیکم

[@zonishah3044]

Plzzzz sir prompt response

[@queennoor6474]

Setallite choromosome ka koi Kam nhi??

[@ranaawais9426]

Sir you told us in this vedio the size of DNA is 5 cm how can it present in the cell whose size is 0.1 to 100 micrometer please answer it

[@khan-kz8fc]

السلام علیکم

[@khan-kz8fc]

DNA condense on histone protien and due to coiling on histone , DNA fit into nucleus.

[@ranaawais9426]

Thank you sir ❤️

[@ranaawais9426]

Wa alikum Assalam

[@khan-kz8fc]

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[@botanywithmalabika5702]

Very good lecture.. But I think one correction needed on name of histone proteins..

[@abdullahbhai8636]

Done sir