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DNA -BASIC STRUCTURE

 DNA-BASIC STRUCTURE  DEOXY RIBO NUCLEIC ACID DNA is a polymer of deoxy ribonucleotides It is composed of monomeric units namely deoxy adenylate(dAMP), deoxy guanylate(dGMP), deoxy cytidylate(dCMP) and deoxy thymidylate(dTMP). The monomeric deoxy nucleotides in DNA are held together by 3’,5’ –phosphodiester linkage ERWIN CHARGOFF RULE/CHARGOFF’S EQUIVALENT RULES 1. The sum of purines is equal to the sum of pyrimidines Pu/Py=1 A+G=T+C 2.The ratio of adenine to thymine is one A/T=1 3. The guanine and cytosine is also one G/C=1 4.Bases with 6 amino group is equal to bases with 6 keto group. A+C=G+T The ratio of A+T/G+C  is known as dissymmetric ratio . It varies greatly from one species of DNA to other When dissymmetry of ratio exceeds 1 such DNA is called A-T type. The value of dissymmetry of human being is 1.4. STRUCTURE OF DNA[WATSON –CRICK MODEL] 1.DNA molecule consist of 2 polynucleotide chains, coiled around each other on the common in the form of righthanded double he...
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BASIC ELEMENTS OF NUCLEIC ACIDS

 

NUCLEIC ACIDS

  • Nucleic acids are polymers of nucleotides held by 3’ and 5’phosphate bridges.
  • These are known as  molecules of hereditary.
  • They are 2 types of nucleic acids
  • DNA[Deoxy ribonucleic acid]
  • RNA[Ribonucleic acid]

ELEMENTS OF NUCLEIC ACID

1.PHOSPHORIC ACID

ii. PENTOSE SUGAR

  • RNA contains Ribose and DNA contains deoxy ribose 
  • RNA and DNA differs in C2 of sugar


iii. NITROGENOUS BASE

  • Two types of nitrogenous base are found in all nucleic acid.
  • They are derivatives of purines and pyrimidines

  • The common pyrimidine derivatives found in nucleic acids are
  • URACIL [2,4 Dioxy pyrimidine-π‘ͺ_πŸ’ 𝑯_πŸ’ 𝑢_𝟐 𝑡_𝟐  ]found in RNA
  • THYMINE[5-methyl (2,4 dioxy pyrimide)-π‘ͺ_πŸ“ 𝑯_πŸ” 𝑢_𝟐 𝑡_𝟐]-Found in DNA
  • CYTOSINE[2-oxy 4- amino pyrimidine-π‘ͺ_πŸ’ 𝑯_πŸ“ 𝑢𝑡_πŸ‘]-Found in both RNA and DNA


PURINES

  • The purine derivative found in nucleic acids
  • Adenine-[6- amino purine-π‘ͺ_πŸ“ 𝑯_πŸ“ 𝑡_πŸ“]
  • Guanine-[2- amino 6-oxy purine-π‘ͺ_πŸ“ 𝑯_πŸ“ 𝑢𝑡_πŸ“]
  • They both found in both DNA and RNA

Hydrolysis of nucleic acids


NUCLEOSIDES

  • The nucleosides are compound in which nitrogenous bases are linked to pentose sugar by 𝛽-glycosidic linkage
  • Nucleosides containing ribose are called ribonucleosides while those possessing deoxy ribose are called deoxy ribonucleoside
  • The H of N9 of purines and H of N1 of pyrimidines eliminating the molecule of water.

Ribonucleosides


DEOXY RIBONUCLEOSIDE


NUCLEOTIDES

  • Nucleotides are phosphoric acid ester of nucleosides.
  • Phosphate is esterified to sugar moiety
  • Nucleotides containing purines are
  • i)Adenylic acid[Adenine nucleotide]
  • ii)Guanylic acid[Guanine nucleotide] 


Nucleotides containing pyrimidines are

  • i)Uridylic acid
  • ii)Cytidylic acid
  • iii)Thymydilic acid

Ribonucleotides


2'-Deoxy ribonucleotides


FUNCTION OF NUCLEOTIDES

1.As the carrier of chemical energy

  • Nucleotides has one,two or three phosphate group covalently link at 5’OH of ribose. The 3’ phosphate group are labelled Ξ±,Ξ² and Ξ³ starting from ribose.
  • The Ξ±Ξ² and Ξ²Ξ³ linkage are phosphoric anhydride.
  • Hydrolysis of ester linkage yield-14KJ/mol
  • Hydrolysis of anhydride linkages yield – 30KJ/mol

2.As the component of enzyme factor

  • Many enzyme cofactor and coenzyme[Coenzyme A,NAD+ and FAD] contains adenosine as part of structure.

3.As chemical messenger

  • The most common messenger is cAMP


References
1.Principles of Biochemistry-Lehinger 
2.Biochemistry-U. Sathyanarayana & U.Chakrapani













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