Question

If a small chromosome consists of 500,000,000 nucleotides, how many nucleosomes will attach to the chromosome?
a) 1000
b) 50,00,00,000
c) 12,50,000
d) 25,00,00,000

Answer 1

Here in the question they have given us a scenario that if a small chromosome has around 500,000,000 nucleotides, we have to find out the number of nucleosomes that will be found attached to the chromosome. Nucleosome is basically a structural unit of DNA packaging that is found in eukaryotes.

Complete answer:
Chromosome is basically a long DNA molecule which has genetic material of an organism. Humans have 23 pairs of chromosomes, out of which 22 pairs are known as autosomes and 1 pair is known as sex-chromosomes.
Nucleotides are those molecules which consist of nucleoside and phosphate. They form the monomeric unit of nucleic acids (DNA & RNA). Basically, each DNA strand is composed of some repeating units which we call nucleotides.
When the DNA strand wraps or wounds around histone octamer, then it will form the structure that is known as nucleosome. The nucleosome is also the fundamental subunit of chromatin.
We know that 1 nucleosome has approximately 400 nucleotides in it, so in order to calculate the number of nucleosomes that are attach to chromosome, we will just divide the total number of nucleotides that is given in the question with the number of nucleotides that is present in the 1 nucleosome –
500,000,000/ 400= 12,50,000

Therefore, the correct answer is option (c).

Note:
The presence of the nucleosome chain gives a bead on string appearance if we look at it under an electron microscope. A nucleosome is formed of the DNA sections 200bp that are wrapped around a core octamer of eight histones. Histones are the special group of proteins that are found in the nuclei of eukaryotic cells.