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This is a DNA molecule, a double helix that encodes the genetic information.
This is a typical depiction of DNA in science fiction movies: two intertwining helices with some sticks in the center.
But let’s show the atoms for one of the DNA strands.
You can see that the structure of DNA is very repetitive, it is the same unit over and over again.
It is this repeating structure that gives DNA its name.
“D”, shown in green, stands for deoxyribose – a sugar molecule.
“N” is quite literally the central part of DNA; it is shown in blue. “N” stands for nucleic bases.
It is this part of DNA that actually encodes the genetic information.
Finally “A” means phosphoric acid, that holds the structure together. It is shown in red.
And of course the second strand consists of the same D, N and A segments.
You can see how Nature efficiently packs the DNA molecule.
The bases stack on top of one another, making the whole structure very compact.
The bases from two strands are very close together, so one would expect some kind of an interaction between them.
And indeed they do form so-called “hydrogen bonds”.
These hydrogen bonds are formed between each pair of bases throughout the molecule.
They prevent the two strands from falling apart.
The function of DNA is just the storage of genetic information, the actual work in the body is done by proteins.
The building block of a protein is an amino acid, and each of the amino acids is encoded by three bases.
So this is the main purpose of DNA: containing the information about the proteins.