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RIBO NUCLEIC ACID -STRUCTURAL FORMS

 RIBO NUCLEIC ACID Ribonucleic acid like DNA is unbranched long macromolecule consisting of ribonucleotides joined by 3’-5’ phosphodiester bond. In eukaryotes t is synthesised in nucleolus and transported to cytoplasm  In prokaryotes it is synthesised in cytoplasm itself  It numbers can be few to many thousands CHARATERISTICS OF RNA  Sugar moiety is ribose sugar RNA contains the pyrimidine uracil (U) in place of thymine RNA contains adenine and guanine and the pyrimidine base uracil and cytosine. Here, adenine always pairs with uracil and guanine always pairs with cytosine. RNA Structure  Primary structure  The native RNA is single-stranded rather than double stranded. The adjacent nucleotides are joined with each other by 3'-5' phosphodiester bonds. Ribose sugars are conjugated with bases by Ξ²-glycosidic linkage. RNA is not strictly complementary and it need not contain complementary base pairs (i.e.) the adenine content does not necessarily equal to uraci...
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RIBO NUCLEIC ACID -STRUCTURAL FORMS

 RIBO NUCLEIC ACID



  • Ribonucleic acid like DNA is unbranched long macromolecule consisting of ribonucleotides joined by 3’-5’ phosphodiester bond.
  • In eukaryotes t is synthesised in nucleolus and transported to cytoplasm 
  • In prokaryotes it is synthesised in cytoplasm itself 
  • It numbers can be few to many thousands

CHARATERISTICS OF RNA 

  • Sugar moiety is ribose sugar
  • RNA contains the pyrimidine uracil (U) in place of thymine RNA contains adenine and guanine and the pyrimidine base uracil and cytosine.
  • Here, adenine always pairs with uracil and guanine always pairs with cytosine.

RNA Structure 

Primary structure 

  • The native RNA is single-stranded rather than double stranded.
  • The adjacent nucleotides are joined with each other by 3'-5' phosphodiester bonds.
  • Ribose sugars are conjugated with bases by Ξ²-glycosidic linkage.
  • RNA is not strictly complementary and it need not contain complementary base pairs (i.e.) the adenine content does not necessarily equal to uracil content nor does guanine content necessarily equal to its cytosine content.
  • RNA is alkali labile and can be hydrolyzed by weak alkali to 2',3'-cyclic diesters of the mononucleotides.
  • RNA is alkali labile and can be hydrolyzed by weak alkali to 2',3'-cyclic diesters of the mononucleotides.


2° Structure of RNA :

  • 2° structure of RNA is probably less justified than in the case of DNA. 
  • There is no evidence for the existence of more than one polyribonucleotide strand in the natural RNAs.
  • However, the complementary base sequence with opposite polarity, the single strand of RNA may fold back on itself like a hairpin and thus acquire the double stranded helical pattern.

  • The hairpin loop regions or the helical regions are stabilised by A-U and G-C base pairs similar to those which stabilise the conformation of DNA.
  • The base pairing in RNA hair pins is frequently irregular because of the irregular base composition. 
  • So, the RNA does not allow the incorporation of the entire molecule into double perfect helix of this type.
  • Some of the opposing bases may not be complementary and so one or more bases along a single strand may be looped out to facilitate the pairing of others. 
  • That’s why the helical region co exist with the random segments as in the following figure.


  • These secondary structured ribonucleotides  classified as
  • mRNA - messenger RNA 
  • tRNA - transfer RNA 
  • rRNA - ribosomal RNA 
  • vRNA - viral RNA
  • Each of these types serves as an extremely important informational links between DNA - the master carrier of genetic information and protein. 
  • The different types of RNA molecules differ from each other by size, function and general stability.
References
1.Principles of Biochemistry-Lehinger 
2.Biochemistry-U. Sathyanarayana & U.Chakrapani
3. Lewin's Genes





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