Question

Which structure of DNA is observed as "Beads on a string" under an electron microscope?

Answer 1

Nucleosomes:

1. The nucleosome is composed of DNA wrapped around eight proteins.
2. Eight proteins function like a spool and are called histone octamer.
3. Under a microscope, it appeared as “beads on a string”.
4. Here, beads represent complexes of histones and DNA.
5. The bead plus linker DNA leads to the next bead and form the nucleosomes.
6. Each bead contains eight histone molecules: two copies each of H2A, H2B, H3, and H4; out of 200 bp DNA, 146 bp DNA is bound tightly around the histone core and the remainder serve as linker DNA between nucleosomal beads.