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2.1.1. DNA

Deoxyribonucleic acid (DNA)

Chemical composition and structure of DNA

DNA is the molecule that contains the genetic information of the cell. Watson and Crick, in 1953, discovered what the structure of DNA was like , which helped them win the Nobel Prize in Medicine in 1962.

The model proposed by Watson and Crick or  the double helix model have the following characteristics:

  • DNA is made up of two chains of nucleotides joined by their nitrogenous bases that are on the inside, while the pentose and phosphoric acid are on the outside. Nitrogen bases are linked by weak bonds, called hydrogen bonds, to their complements. Adenine (A) always binds thymine (T) and guanine (G) with cytosine (C).
  • The two chains are antiparallel, that is, parallel but in the opposite direction.

DNA properties

  • DNA contains the information necessary to regulate protein synthesis. Depending on the sequence of nitrogenous bases of the nucleotides, some proteins or others will be synthesized.
  • The information contained in the DNA of a cell is passed on to the next generation of cells, since through DNA replication, copies of the DNA are made and transmitted to daughter cells. Thus, in a multicellular being that comes from an egg or zygote cell, all cells have the same DNA.

DNA location

Depending on the type of cell, DNA is found in different places:

  • In eukaryotic cells: DNA is in the nucleus, it is surrounded by the nuclear envelope. It is made up of two chains of nucleotides joined to proteins forming chromatin which, when the cell condenses to divide, becomes chromosomes.
  • In prokaryotic cells: DNA forms a circular, double-stranded bacterial chromosome , without any nuclear envelope, so it is free in the cytoplasm. Some bacteria also have other circular DNA fragments called plasmids.
  • In viruses: DNA can be single or double-stranded, linear or circular.