Packaging Of DNA Helix || Molecular genetics || Neet Biology || Class 12

Packaging of DNA helix
The distance between two consecutive base pairs is 0.34nm (0.34×10-9m) of the DNA double helix in a typical mammalian cell.
When the total number of base pairs is multiplied with the distance between two consecutive base pairs (6.6 × 10-9 × 0.34 ×10-9
m/bp), the length of DNA double helix is approximately 2.2 m. (The total length of the double helical DNA = total number of base pairs × distance between two consecutive base pairs).
If the length of E. coli DNA is 1.36 mm, the number of base pairs in E. coli is 4 ×106
m (1.36 × 103 m/0.34 ×10-9).
The length of the DNA double helix is far greater than the dimension of a typical mammalian nucleus (approximately 10-6 m).
How is such a long DNA polymer packaged in a cell?
Chromosomes are carriers of genes which are responsible for various characters from generation to generation. Du Praw (1965)
proposed a single stranded model (unineme), as a long coiled molecule which is associated with histone proteins in eukaryotes.
Plants and animals have more DNA than bacteria and must fold this DNA to fit into the cell nucleus.
In prokaryotes such as E. coli though they do not have defined nucleus, the DNA is not scattered throughout the cell.
DNA (being negatively charged) is held with some
proteins (that have positive charges) in a region called the nucleoid.
The DNA as a nucleoid is organized into large loops held by protein.
DNA of prokaryotes is almost circular and lacks chromatin organization, hence termed genophore.
In eukaryotes, this organization is much more complex.
Chromatin is formed by a series of repeating units called nucleosomes.
Kornberg proposed a model for the nucleosome, in
which 2 molecules of the four histone proteins H2A, H2B, H3 and H4 are organized to form a unit of eight molecules called histone octamere.
The negatively charged DNA is wrapped around the positively charged histone octamere to form a structure called nucleosome.
A typical nucleosome contains 200 bp of DNA helix.
The histone octameres are in close contact and DNA is coiled on the outside of nucleosome.
Neighbouring nucleosomes are connected by linker DNA (H1) that is exposed to enzymes.
The DNA makes two complete turns around the histone
octameres and the two turns are sealed off by
an H1 molecule.
Chromatin lacking H1 has a beads-on-a-string appearance in which DNA enters and leaves the nucleosomes at random places.
H1 of one nucleosome can interact with H1 of the neighbouring nucleosomes resulting in the further folding of the fibre.
The chromatin fiber in interphase nuclei and mitotic chromosomes have a diameter that vary between 200-300 nm and represents inactive chromatin.
30 nm fibre arises from the folding of nucleosome, chains into a solenoid structure having six nucleosomes per turn.
This structure is stabilized by interaction between
different H1 molecules.
DNA is a solenoid and packed about 40 folds.
Additional set of proteins are required for packing of chromatin at higher level and are referred to as non-histone chromosomal proteins (NHC).
In a typical nucleus, some regions of chromatin are loosely packed (lightly stained) and are referred to as euchromatin.
The chromatin that is tightly packed (stained darkly) is called heterochromatin.
Euchromatin is transcriptionally active and heterochromatin is transcriptionally inactive.
DNA Replication
Replication of DNA takes place during the
S phase of cell cycle.
During replication, each DNA molecule gives rise to two DNA strands, identical to each other as well as to the parent strand.
Three hypotheses of DNA replication have been proposed.
They are conservative replication, dispersive replication, and semi conservative replication.
In conservative replication, the original double helix serves as a template.
The original molecule is preserved intact and an entirely new double stranded molecule is synthesized.
In dispersive replication, the original molecule is broken into fragments and each fragment serves as a template for the synthesis of complementary fragments.
Finally two new molecules are formed which consist of both old and new fragments.

[@devithiyagu6605]

Clear explanation with gud understanding pics sir............................................................. 🤩🤩🤩🤩🤩🤩🤩🤩🤩🤩🤩🤩

[@MAGESHBIOLOGY]

Thank you

[@sangeesangeetha8760]

Sir your teaching is very useful for me cause ur explanation is like line by line... Actually We don't want to read lesson if we saw ur video.

[@MAGESHBIOLOGY]

Thank you🙏

[@ramansivalingam7302]

Sir ....when my teacher taught this lesson l am not understand fully and lot of doubt in this topic.but when I saw your videos I am cleared and prepare for my exam.thank u anna so much....

[@MAGESHBIOLOGY]

You are always Welcome 🎉. Thank you for ur comments of appreciation🙏

[@ramansivalingam7302]

Thanks sir and upload more videos....

[@karthigakarthiga9221]

Best bio class I found in tamil anna ....❤🎉❤

[@MAGESHBIOLOGY]

Thank you sister👭

[@karthigakarthiga9221]

​@@MAGESHBIOLOGY 😊❤

[@manoharanperumal8857]

Vera level explanation sir👌🏼👌🏼👌🏼👌🏼👌🏼👌🏼👌🏼👌🏼👌🏼

[@MAGESHBIOLOGY]

Thank you

[@manoharanperumal8857]

👌🏼

[@user-jc9si6nn7r]

Thank you sir

[@pikachuaddictz5056]

Your video very useful in this corono time awesome explaination

[@MAGESHBIOLOGY]

Thank you

[@yasodhap4429]

Super

[@jashwanthraj9952]

sir it was a super video thank you sir

[@MAGESHBIOLOGY]

You are most welcome

[@Sekarnrasi]

Sir.. I was saying in all vdos ..that ur teaching is marvelous.. and ur teaching is very ec to understand... & Tq sir..🙏🙏🙏🙏

[@MAGESHBIOLOGY]

Thank you 🙏 u r most welcome🙏🎉🙏

[@shanmugamshanmugam1159]

You are good biology teacher .in my life i doesnot ever seen like you anna.

[@MAGESHBIOLOGY]

Thank you thambi🥰🙏🙏🙏🥰

[@devithiyagu6605]

Sir..... Waiting for nxt vdo.......🎥🎥🎥

[@MAGESHBIOLOGY]

Today or tomorrow morning will be uploaded

[@devithiyagu6605]

@@MAGESHBIOLOGY kk sir... ☺

[@9444875264]

Nice explanation sir👏

[@MAGESHBIOLOGY]

Thank you🙏🙏🙏 sam

[@santhoshinisk6718]

Thanks a lot sir
unga yalla videos romba useful uh eruku very clear explanation just oru vaati unga video paatha podhum concept clear uh puriyudhu.
You are the best teacher 💐
pls continue this sir it will be useful for many students

[@MAGESHBIOLOGY]

Thank you🙏🙏🙏🙏

[@kalaivanis8265]

Explaination super sir

[@MAGESHBIOLOGY]

Thank you🙏

[@swetharavichandran5950]

Anna what's the difference between nucleoid and nucleosome???plsssssssss tell me🙏🙏🙏

[@MAGESHBIOLOGY]

Nucleosomes are the basic unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a histone protein core while nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of a prokaryote that contains all or most of the genetic material

[@kishore12321]

Thanks you so much sir

[@MAGESHBIOLOGY]

You are most welcome

[@Manikandanpqfs]

Romba super ah nadathuringa sir

[@MAGESHBIOLOGY]

Thank you thambi

[@iamranjithram26]

I came for 08:11 - 08:25 and now i understood this

[@MAGESHBIOLOGY]

🙏

[@humblee2]

Superb sir.

[@MAGESHBIOLOGY]

Thank you thambi

[@jeevat5947]

Super such a useful channnel,keep rocking for ever,sir👍👍👍👍

[@MAGESHBIOLOGY]

Thank you🙏

[@Monicapd]

Superb sir 👍👍well done.... 👏👏👌clearly explained...

[@MAGESHBIOLOGY]

Nandri

[@lakshmivl1808]

really understood clearly Sir Thank you.

[@MAGESHBIOLOGY]

You are most welcome

[@rajasekark7131]

thalaiva nee vera levelu..

[@MAGESHBIOLOGY]

Thank you🙏

[@chandrasabapathy5743]

👌👌👌 super

[@MAGESHBIOLOGY]

Thank you🙏🙏

[@chitramanikandan3973]

Tqq so much sir

[@MAGESHBIOLOGY]

You are most welcome🎉

[@077-sinraj.v7]

Thanks for your videos anna ❤️

[@MAGESHBIOLOGY]

You are most welcome

[@madhumithas.m8628]

Sir really ur great🔥 tnku soo much sir👍😁

[@MAGESHBIOLOGY]

Thank you🙏 and welcome🎉👏🎉

[@madhumithas.m8628]

Tnx sir upload more videos😁

[@MAGESHBIOLOGY]

Sure👍👌

[@deepajayavelu404]

Super sir your video is very useful for me

[@vinothini.v6561]

Nice teaching sir 👌 superb👍

[@MAGESHBIOLOGY]

Thank you thambi

[@sathishseeralan4015]

nice

[@ushakumari3874]

I'm very interested in ur teaching sir😁 so I'll see all ur videos regularly🙏🏻🙏🏻🙏🏻

[@MAGESHBIOLOGY]

Thank you so much 🍫🍫

[@ushakumari3874]

@@MAGESHBIOLOGY u r great sir !simple and humble😻

[@MAGESHBIOLOGY]

Not great but simple 🙃 thank you 🍫🍫🍫

[@ushakumari3874]

@@MAGESHBIOLOGY 😄🙈😄

[@naturaleducation61]

Your teach is excellent

[@MAGESHBIOLOGY]

Thank you🙏

[@ammukutty65]

Clear explanation sir..

[@MAGESHBIOLOGY]

Thank you

[@RameshR-yk3kh]

Ninga epdi bro padikurenga

[@nareshselvarajan7918]

Excellent explanation sir

[@MAGESHBIOLOGY]

Thank you🌹

[@marychemistry9767]

Clear explanation sir

[@MAGESHBIOLOGY]

Thank you

[@monishahv1344]

Awesome explanation sir👏👏🔥

[@MAGESHBIOLOGY]

Thank you

[@rsm3188]

Super sir

[@MAGESHBIOLOGY]

Thank you

[@akalyaselvaraj3253]

👌👌👌

[@MAGESHBIOLOGY]

Thank you

[@ganeshm3468]

Super sir 👏

[@MAGESHBIOLOGY]

Thank you🙏

[@gamingwithtamilpasanga4848]

Nega clg mudichitigla anna

[@MAGESHBIOLOGY]

Mudichittean thambi

[@palanisamysamy3585]

How to contact you sir

[@K.k8998]

How to find the base pair in dna

[@devithiyagu6605]

😇😇😍😍😎😎

[@MAGESHBIOLOGY]

🤔🤔🤔

[@devithiyagu6605]

@@MAGESHBIOLOGY Sir enga iruthu pic collect panringa

[@devithiyagu6605]

All pics are osum sir... 😎

[@MAGESHBIOLOGY]

Company secret velila sollapidathu... 😀😀😀😀 books and net

[@devithiyagu6605]

Oohhh oohhh kk sir😃

[@sathishseeralan4015]

bro after these please upload evolution

[@MAGESHBIOLOGY]

Ok bro

[@remaasri9799]

Spr bro

[@MAGESHBIOLOGY]

Welcome

[@mukunthanz]

Sooper teaching bro... where are you from

[@MAGESHBIOLOGY]

Thank you bro

[@K.k8998]

Say the calculations length of dna

[@MAGESHBIOLOGY]

The length of DNA segment is calculated by finding the number of base pairs and multiplying it by the distance between adjoining base pairs.

[@dhanushganesh1468]

Helix meaning solluga anna

[@MAGESHBIOLOGY]

Helix is strand or shape of molecules for example..
The double helix is a description of the molecular shape of a double-stranded DNA molecule

[@palanisamysamy3585]

Good explanation 👏 👍 👌 😀 🙌 😄 👏 👍 👌 😀 useful me sir
Pls more videos
Keep it up
God bless you
If you free pls contact me sir
I have more doubts others topic

[@eswaris6314]

Super

[@pawanpawan3659]

Thank you sir.

[@MAGESHBIOLOGY]

You are most welcome🎉

[@yasodhap4429]

Super

[@abubackersiddiq7656]

Thank you sir

[@MAGESHBIOLOGY]

You are most welcome🎉