Question

What are the structures that give an appearance of ‘beads on a string’ in the chromosomes known as?

• A. Nucleoproteins
• B. Nucleotides
• C. Nucleosomes
• D. Nucleosides

Answer 1

The correct option is C Nucleosomes

Nucleosomes appear as ‘beads on string’ in the chromosome when viewed under an electron microscope. The beads are the histone proteins and DNA. The bead along with the connecting DNA that is wound around it forms the nucleosome. The nucleosome is the fundamental unit of organization on which the higher order packaging of chromatin is built. The bead of each nucleosome contains eight histone molecules in which two copies each of H2A, H2B, H3 and H4 are found.


A nucleotide is the monomer of a polynucleotide chain (DNA or RNA). It is made of three components - a nitrogenous base, a pentose sugar (ribose in case of RNA and deoxyribose for DNA), and a phosphate group. There are two types of nitrogenous bases – purines (adenine and guanine), and pyrimidines (cytosine, uracil and thymine).

Nucleoside is a unit made up of nitrogenous base and pentose sugar without phosphate group.
Nucleoside = Nucleotide - Phosphate group

Nucleoproteins are proteins like ribosomes which are associated with nucleic acids (RNA or DNA).