Pharmacognosy - medicinal plants (herbs)
Pharmacognosy - medicinal plants (herbs)

Theme XVIII: Heterocycles

Structure of nucleic acids

Structure of nucleic acids. Biological significance. Mononucleotides. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

Nucleic acids

Nucleic acids are formed of units of mononucleotides, which participate in the molecular mechanisms through which it is stored, replicated and transcribed the genetic information and protein synthesis.

Are structured by a nitrogenous base (purine or pyrimidine), a pentose (C 5 sugar) and phosphoric acid.

Schematically, a mononucleotide can be like this:

These nitrogenous bases can be:


Pyrimidine:
Uracil - Thymine - Cytokine

Purine:
Adenine – guanine


The deoxyribonucleic acid (DNA) and the ribonucleic acid (RNA) are formed from successive units of mononucleotide.


DNA molecules of all types of cells contain mononucleotide units with different frequencies linked by phosphodiester bonds located between the 3'-hydroxyl position of the pentose of one unit and the 5'-hydroxyl group of the pentose of the next unit.


Their constituent sugar is deoxyribose and the nitrogenous bases mentioned above in composition that may vary from one species to another. The function of the DNA is to carry the genetic information.
 
The ribonucleic acids are three basic types:
     • messenger RNA (mRNA)
     • transfer RNA (tRNA)
     • ribosomal RNA (rRNA)

Each has a specific molecular weight and a certain base composition. The three variants are in multiple molecular species.


Like the DNA, the three types of RNA are linear polymers of successive mononucleotides bonded by bridged 5'-3'-phosphodiester.
 
The sugar is ribose and the nitrogenous bases are adenine, guanine, cytosine and uracil.
 
The RNA has in its structure the uracil and an additional hydroxyl group and in the DNA is the thymine.

DNA structure

DNA

RNA


Structural difference between DNA and RNA

see also

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