Question

How can 6 feet of DNA fit in the nucleus of a human cell?

Answer 1

Hint: DNA is a long polymer of deoxyribonucleotide. A nucleotide is composed of three components- Nitrogenous base, Pentose sugar, and a Phosphate group. DNA acts as a genetic material in most of the organism and carries genetic information from one generation to the other generation. The segment of DNA which codes for protein is known as gene.

Complete answer:
The length of DNA is usually defined as the number of the nucleotides present in them. It is also considered as a characteristic of an organism. The haploid content of human DNA is $3.3 \times 10^9$ base pairs.
In humans, the negatively charged DNA is wrapped around the positively charged histone October to form a structure called nucleosome to fit in the nucleus. Histones are positively charged due to the presence of basic amino acids like lysine and arginine.
Histones is an octamer molecule made up of H2A, H2B, H3 and H4 molecules. There is a H1 histone molecule which is also known as linker histone.
Nucleosome contains 200 bp of DNA helix. Nucleosomes constitute the repeating unit of a structure in the nucleus called chromatin fibre, thread like structure. The nucleotides in chromosomes when viewed under electron microscope are seen as beads on string structure. These histone help in packing the DNA compactly thus making it fit in a small nucleus.

Note:
The length of the DNA double helix in a typical mammal is calculated by multiplying the distance between two consecutive base pairs i.e, 0.34 nm with the total number of base pairs, that is, $6.6 \times 10^9$ base pairs.
The approximate length of a human DNA comes out to be 2 meters long which is equal to 6 feet. A length far greater than the dimension of a typical nucleus.