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5.2.1. DNA structure

DNA structure

The DNA  is a polymer of nucleotides of adenineguaninecytosine and thymine, connected by links phosphodiester, in which a phosphate group is bonded by two ester links two successive nucleotides.

When two nucleotides are joined by phosphodiester bond, the resulting dinucleotide has, at one end, a phosphate group on carbon 5 that remains free, and can be attached to a hydroxyl group on carbon 3 of another nucleotide. At the other extreme, the hydroxyl group of carbon 3 is also free, available to react with the phosphate of carbon 5 of another nucleotide. Thus, long nucleotide chains can be formed that will always have a free 5 'phosphate group at one end and a free 3' hydroxyl group at the other.

The nucleotide sequence of a nucleic acid is written from left to right, from the 5th to 3rd carbon end.

A short-stranded nucleic acid is called an oligonucleotide (generally up to 50 nucleotides) and if its length is greater, a polynucleotide .

In eukaryotic cells , DNA is located in the nucleus , although mitochondria  and chloroplasts also have DNA .

The DNA of the nucleus is associated with proteins called histones and other non-histone proteins. These proteins are nucleoproteins.

The DNA of mitochondria and chloroplasts is distinct from nuclear DNA, much like the DNA of prokaryotes. This DNA forms a nucleoid that lacks a nuclear envelope, and is also associated with other proteins.

Fundamental ideas about the structure of DNA

DNA structure