Chat with tutor

Ask Questions, Get Answers

Questions  >>  CBSE XII  >>  Biology

Shown above is the electron micrograph (EMI) picture of 'beads-on-string'.

(a)Identify and explain the detailed structure of a bead with the help of a labelled diagram.

(b) Describe the packaging of ‘beads –on -string' in a eukaryotic cell.

1 Answer


b. * The bead-like structures are the nucleosomes.
* Organization is much more complex.
* There is a set of basic proteins called histones.
* Depending upon the abundance of amino acid residues with charged side chains, a protein acquires charge.
* Histones are rich in basic amino acid residues-Lysine and Argenine which carry positive charges in their side chains.
* Histones are organized to form a unit of 8 molecules called a histone octomer.
* Negatively charged DNA is wrapped around positively charged histone octomer to form a nucleosome.
* A typical nucleosome consists of 200BP of double helix.
* The repeating units of chromatin are made up of nucleosomes.
* Nucleosomes in chromatin are seen as beads on a string.
* Chromatin further coils and condenses to form the chromosomes.
* Packaging of chromatin at higher level needs additional set of proteins that are collectively called Non histone chromosome proteins (NHC proteins).
* Some regions of chromatin are loosely packed and stains light and are called euchromatin. This is active transcriptionally.
* Some regions of chromatin that are densely packed and stains dark are called heterochromatin. This is transcriptionally inactive.
Help Clay6 to be free
Clay6 needs your help to survive. We have roughly 7 lakh students visiting us monthly. We want to keep our services free and improve with prompt help and advanced solutions by adding more teachers and infrastructure.

A small donation from you will help us reach that goal faster. Talk to your parents, teachers and school and spread the word about clay6. You can pay online or send a cheque.

Thanks for your support.
Please choose your payment mode to continue
Home Ask Homework Questions
Your payment for is successful.
Clay6 tutors use Telegram* chat app to help students with their questions and doubts.
Do you have the Telegram chat app installed?
Already installed Install now
*Telegram is a chat app like WhatsApp / Facebook Messenger / Skype.