Nucleic Acids

 

Nucleic Acids

Nucleic Acids
Nucleic Acids

Nucleic acid are formed by the hydrolysis of nucleoproteins.
There are two classes of nucleic acid 
RNA – ribonucleic acids
DNA – deoxyribonucleic acids
Nucleic acid are polymers of nucleotides. Nucleotides is a phosphoric ester of nucleoside.
Nucleoside are hydrolyzed by Aqueous
ammonia at 175⁰ C to give nucleusides and phosphoric acid.
Nucleosides contain Purine or pyrimidine bases and sugar, ribose or deoxyribose. These are adenosine, deoxyadenosine, guanosine, deoxyguanosine, cytidine, deoxycytidine, uridine, deoxythymidine.
Nucleosides hydrolyse into purine and pyrimidine bases. There are adenine, guanine, thymine, cytosine, and uracil. 
Uracil occurs in RNA whereas, DNA contain thymine in the place of uracil.
DNA is made up of double stranded nucleic acid chains, which are closely associated with each other by means of hydrogen bonds with base pairs. Adenine pairs with Thymine (A – T) and Guanine pairs with Cytosine (G – C) and 
A + G = T + C  ( Chargaff’s rule).
Waston Crick  model is based upon Chargaff’s rule which states that hereditary information is transmitted to offspring by the process of DNA replication. 
RNA is of three types, m-RNA, t-RNA and r-RNA. There are much smaller than DNA and occur as single strand. All these take part in protein synthesis.
Synthesis of m-RNA from DNA in the presence of enzyme RNA polymerase is known as transcription.
Segment of DNA molecule that codes for the biosynthesis of one complete polypeptide chain is called a Gene.
Synthesis of protein by m-RNA in ribosomes is called translation. The ribonucleotide sequence in m-RNA form a code which determine the order of different amino acids and this code is read by t-RNA in the process of translation.
Each t-RNA contains in its structure a sequence of three ribonucleotides complementary to the codon sequence known as anticodon.
Adenine can be synthesized from 2,6,8- trichloropurine (Fischer synthesis) and from phenylazomalenonitrile (Todel et.al. synthesis).
Adenine combines with ribose and deoxyribose sugar to form adenosine and deoxyadenosine nucleotides respectively.
Guanine can be synthesized by treating 2,6,8-trichloropurine with ammonia in KOH (Fischer synthesis) and from Guanidine (Traube synthesis).
Guanine combines with ribose and deoxyribose sugars to form Guanosine and deoxyguanosine respectively.
Guanine when treated with nitrous acid gives Xanthine.
Cytosine can be synthesized from s-ethylisothiourea and sodioformyl acetic ester (Weeler and  Johnson synthesis) and from malondialdehyde acetal and hydroxylamine hydrochloride ( Tarsio et al . synthesis ).
Guanine when treated with nitrous acid gives Xanthine.
Hydroxymethyl cytosine can be synthesized from ethoxymethylene cyanoacetate ( ulbricht et al . synthesis ) Cytosine also combines with ribose and deoxyribose sugars to form cytidine and deoxycytidine nucleosides respectively .
Uracil can be synthesized from malic acid in the presence of fuming sulfuric acid . 
Uracil can also be synthesized from Urea and ethylacrylate ( Fischer , Roeder synthesis ).
Uracil combines with only ribose sugar to form uridine nucleotide .
Thymine can be synthesized by treating ethylmethacrylate with Urea ( Fischer and Roeder synthesis ) and from thioures and sodioformyl propionic ester ( Wheeler & liddle synthesis ) . 
Thymine combines with deoxyribose sugar to form deoxythymidine nucleoside .

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