Question

The structure called beads on strings are
A. Nucleosomes
B. Base pairs
C. Genes
D. Nucleotides

Answer 1

Hint: Chromosomes are the thread-like structure, which is present in the nucleus of the cells of animals and plants. Chromosomes carry genetic information, which is transferred to the next generation, each of the chromosomes is made up of protein and DNA molecules.

Complete answer:
The chromosomes are the highly coiled structure that carries information. The beads of the string are called nucleosomes and it is the basic structural unit of DNA packaging, that consists of a DNA segment wrapped around a protein that is composed of eight-unit together called histone octamer. Together with the number of nucleosomes structure they form solenoid chromatin fibre. The DNA carries a negative charge and is neutralized by the positive charge of the histone molecule.
The formation of nucleosome starts with a stretch of DNA which is double-stranded coiled which is wrapped around the eight protein molecules called histone protein or histone octamers. each of the histone octamers is consists of the copies of H2A, H2B, H3, and H4. the core part of the Nucleosome contains 146 base pairs of the DNA molecule. the binding of Histone protein with DNA segment is not evenly distributed due to the presence of two types of binding, that named as alpha1, alpha1 and second is L1 and L2 loops.
Two nucleosomes are joined or linked by a stretch of DNA segment called linker DNA. the partial digestion of chromatin structure by the DNAse will revels the structure of nucleosomes. Nucleosomes carry epigenetically inherited information and their position in chromosome help to determine the accessibility of DNA.
Hence, the correct option is A.

Note: Chromatin is a complex form of DNA and protein molecule present in eukaryotic cells, that function is the packaging of the long stretch of DNA tread more densely. The chromatin is of two types such as euchromatin which is a genetically active component while heterochromatin is not active.