Question

The length of DNA molecules greatly exceeds the dimension of the nucleus in eukaryotic cells. How is the DNA accommodated?
A. Deletion of non-essential genes
B. Supercoiling in nucleosomes
C. DNase digestion
D. Through elimination of repetitive DNA

Answer 1

Deoxyribonucleic acid (DNA) is a molecule that contains the biological instructions that make each species unique DNA along with the instructions it contains is passed from adult organisms to their offspring during reproduction.

Complete answer:
Histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin acting as spools around which DNA winds and play a role in the gene regulation. Without histones, the unwound DNA in chromosomes would be very long with a length to width ratio of more than $10$ million to $1$ in human DNA.

For example: each human cell has about $1.8$micrometres DNA, (approx. $6.ft$) but wound on the histones it has about $90$ micrometres $\left( {0.09mm} \right)$ of chromatin. Which, when duplicated and condensed during mitosis results in about $120$ micrometres of chromosomes. So, DNA is accommodated by supercoiling in nucleosomes.

Additional information: A phosphate back bone is the portion of the DNA double helix that practices structural support to the molecule. DNA consists of two strands that wind around each other like a twisted ladder. Each strand has a backbone made up of alternating sugar (deoxyribose) and phosphate groups.

Therefore, from the above explanation the correct option is (B) Super-coiling in nucleosomes.

Note: DNA which is too lengthy is kept condensed and supercoiled inside the chromosomes. This is then seen inside the nucleus of the eukaryotic cell. Supercoiling of DNA reduces the spaces and allow for much more DNA to be packaged.