The structure of chromosomes
Interphase cell chromosomes
The life span of the cell in which it is not dividing is called interphase.
Interphase cell chromatin, as already mentioned, is a mass of filaments called chromosomes. If we could separate the chromosomes one by one from a human interphase cell, we would get 46 filaments, logos and fines. Placed in line, the human chromosomes would form a 5 cm long wire, invisible under the optical microscope, since their thickness does not exceed 30 nm.
Chemical constitution and architecture of chromosomes
Discovering the chemical nature of chromosomes was an arduous task that mobilized hundreds of scientists and many years of work. The first chromosomal constituent to be identified was deoxyribonucleic acid, DNA.
In 1924, German researcher Robert J. Feugen developed a special staining technique that showed that DNA is a major component of chromosomes. A few years later, it was discovered that chromatin is also rich in proteins called histones.
Division cell chromosomes
When the cell divides, the nucleus and chromosomes undergo major modifications. Preparations for cell division begin with the condensation of chromosomes, which begin to curl about themselves, becoming progressively shorter and thicker until they look like compact sticks.
During chromosomal condensation, eucromatic regions coil more loosely than heterochromatic regions, which are condensed even during interphase. In the condensed chromosome, heterochromatins, due to this high degree of packing, appear as “strangled” regions of the chromosome stick called constrictions.