Structures called beads on string are:

Question

Accepted Answer

The correct option is 1:

Nucleosomes are the fundamental repeating structural units of chromatin, which is the complex of DNA and proteins found in the nucleus of eukaryotic cells. Imagine a very long string, which represents the DNA, and beads threaded onto that string, which represent the nucleosomes. Each nucleosome consists of a segment of DNA wound around a core of eight histone proteins (an octamer). This arrangement allows the immensely long DNA molecule to be compactly packaged within the small confines of the cell's nucleus. This "beads on a string" appearance is visible under an electron microscope and is the first level of DNA packaging. This organization is crucial for regulating gene expression and for the orderly segregation of chromosomes during cell division.

The incorrect option is 2: Base pairs.
Base pairs are the fundamental units of the DNA ladder, forming the rungs between the two strands of the DNA double helix. While essential for genetic information, they refer to the individual bonding of nitrogenous bases (A-T, G-C) and do not describe the higher-order packaging structure of DNA.

The incorrect option is 3: Genes.
Genes are specific sequences of DNA that carry the instructions for making proteins or functional RNA molecules. They are units of heredity but represent a functional segment of DNA, not the structural packaging unit of DNA within the nucleus.

The incorrect option is 4: Nucleotides.
Nucleotides are the individual building blocks of DNA and RNA. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. They are the monomer units that link together to form the long polymer chains of nucleic acids but do not represent the "beads on a string" structure of packed DNA.