DNA (or deoxyribonucleic acid) is a molecule found in all cells. It kind of works “Plan“, Unique to each person from which our organism is created and functions. But how is this information recorded in our body? Do our cells all have the same DNA?” Science and future Dive into the heart of our cells to explain.

Genetic information is contained in the nucleus of our cells

The human body is made up of billions of cells. Genetic information is found in the nucleus of these cells. In the nucleus, genetic information is contained in our chromosomes. They are made up of DNA, which are made up of two strands wrapped together to form a double helix. The chromosomes carry our genes, about 25,000. Genetic information is distributed over 46 chromosomes (23 pairs). For each pair, there is one chromosome of paternal origin and one chromosome of maternal origin.

Representation of a chromosome (x-shaped on the left). Chromatin (to which DNA is packed) opens and reveals eight pink regions. These “balls” are histones surrounded by a single strand of DNA. The latter takes place in a double helix and reveals its structure (its base). photo Credit : JACOPIN / BSIP / BSIP via AACP

The same DNA in all nuclei.

“We have about three billion base pairs of DNA. But it’s not all “naked”. It is associated with proteins called histones, which form chromosomes “,” We Pierre Netter, geneticist and explains Researcher from Paris Seine Institute of Biology (CNRS / Sorbonne University).

Histones condense and DNA into chromosomes in an ordered manner. “The expression of genes depends on these histones. They can be active or inactive. Depending on the program that the cells have attached themselves to, the liver cell will not be the same as the brain cell. If genes are expressed. Then The body will make the right cell at the right place, for example, the liver cell and the brain cell are not in the liver.“”Realization of plans“Imprinted in our DNA is affected by a mechanism called transcription. During transcription, a segment of DNA is copied into a transient intermediate carrier in RNA, which makes it possible to synthesize essential proteins.”

While all these mechanisms may seem complex, the genetic information is the same in all nuclei. “In general, a priori, yes, all of our cells have the same DNA from a chemical point of view, except for only a few mutations. There are always some rare mutations, which have extremely low rates. The mutation rate is about 1 in 1 billion and, fortunately, otherwise it will lead to disasters“ Mutations can lead to the development of diseases, such as abnormal numbers of chromosomes 21 when the parents become gametes, which leads to the development of trisomy 21. Genetic disorders can be the cause of it all. Types of diseases. “When we analyze cancer cells, we see that it is “nonsense”. We discover altered chromosomes, absent or extraterrestrial”

Immunoglobulin, “extravagant” cells

There is a type of cell that survives this rule. These are the cells that make it possible to make other cells, immunoglobulin (of the antibody family).Immunoglobulins are amazing“, Explains Pierre Netter.”Imagine a gene whose different regions are called A, B, C and D. When expressed, it forms a protein that contains amino acids. [les bases du code génétique, ndlr] Are ABC and d. Immunoglobulin has a specialized, very efficient system. There will be a fixed number of A’s on the chromosome, numbered A1, A2, A3 ditto B1 B2 B3 etc. It is all present on the chromosome. But when the cell has to specialize to produce an antibody, development has established a very complex system of rearrangement. When these particular cells are going to produce genes to make antibodies, recombinations like A1 and B2, C2 and D3 are going to happen. Physically at that time, the A1 would find itself welded to the B6. This is an extraordinary method that makes it possible to produce genetic diversity “. Immunoglobulins are the only cells whose DNA will be permanently modified. Then it is impossible to go back and this combination will remain in the memory of the organism.