{"id":9554,"date":"2026-06-01T21:33:48","date_gmt":"2026-06-01T21:33:48","guid":{"rendered":"https:\/\/kapdec.com\/help\/?p=9554"},"modified":"2026-06-01T21:33:48","modified_gmt":"2026-06-01T21:33:48","slug":"nucleic-acids","status":"publish","type":"post","link":"https:\/\/kapdec.com\/help\/nucleic-acids\/","title":{"rendered":"Nucleic Acids"},"content":{"rendered":"

Unit: Chemistry of life<\/strong><\/h2>\n

Chapter: Nucleic acids<\/strong><\/h3>\n

Reference: <\/em><\/strong>Nucleic acids, Role of nucleic acids, The difference between DNA and RNA, Nucleotides<\/em><\/p>\n

 <\/em><\/strong>Learning objectives<\/strong><\/p>\n

    \n
  • To understand the structure of nucleic acids<\/li>\n
  • Able to differentiate between DNA and RNA<\/li>\n
  • To understand the detailed structure of DNA<\/li>\n<\/ul>\n

    Nucleic acids<\/strong><\/p>\n

      \n
    • Nucleic acid are polymers of nucleotides and are of two types, Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).<\/li>\n
    • Nucleic acid is composed of pentose sugar (deoxyribose and ribose), nitrogenous bases (purines and pyrimidines) and phosphoric acid.<\/li>\n
    • Purines are double ring structure with N at positions 1,3,7 and 9.<\/li>\n
    • Pyrimidines are six membered single ring structure with N at 1, and 3 position.<\/li>\n<\/ul>\n

                                 \"\"                      <\/p>\n

                           Fig.1. Structure of nitrogenous bases<\/p>\n

       <\/p>\n

                             \"\"                          <\/p>\n

                            Fig.2. Structure of pentose sugar<\/p>\n

       <\/p>\n

       Role of nucleic acids:<\/strong><\/p>\n

      The most vital role of nucleic acids in living beings is to store genetic information; they are created with four bases. An isolated strand of nucleic acid has sufficient information about the organism, and the nucleic acid molecules contain and copy genetic information.<\/p>\n

      The difference between DNA and RNA-<\/strong><\/p>\n

      \"\"<\/p>\n

        \n
      • DNA is present inside nucleus and in chloroplast and mitochondria.<\/li>\n
      • Mitochondrial DNA (mt DNA) is circular and contains about 16,500 nucleotide s. It has information for synthesis of 2 – rRNA and 22-tRNA. It is inherited from mother through female gamete. It also has low mutation rate but does not show genetic recombination.<\/li>\n
      • DNA is naked inside a prokaryotic cell as it lacks nuclear membrane and histone protein, often called nucleoid. Many prokaryotic cells, like bacteria also have extra chromosomal DNA called plasmid.<\/li>\n
      • The length of DNA is usually defined as number of nucleotides (or a pair of nucleotides referred to as base pairs) present in it and also the characteristic of an organism. For ex. φ ×174 has 5386 nucleotides, Bacteriophage lambda has 48502 base pairs (bp), Escherichia coli has 4.6× 106 bp, and haploid content of human DNA is 3.3 × 109 bp.<\/li>\n<\/ul>\n

        Nucleosides- formed by the association of pentose sugar with nitrogenous bases. The linkage between nitrogenous base and pentose sugar is a glycosidic bond (N-glycosidic linkage).<\/p>\n

          \n
        • nucleosides formed from purines- they have 1’-9 glycosidic linkage, formed between 1’ carbon of pentose sugar and 9th position of A\/G.<\/li>\n
        • nucleosides formed from pyrimidines- they have 1’-1 linkage, formed between carbon 1’ of pentose sugar and 1st position of T\/C.<\/li>\n<\/ul>\n

                                         \"\"                   <\/p>\n

           Fig.3. Glycosidic bond in the nucleoside, A. linkage of cytosine to deoxyribose and B. linkage of adenosine to deoxyribose.<\/p>\n

          Nucleotides<\/strong>– they are the phosphate ester of nucleoside. A nucleotide has nitrogenous base, pentose sugar and phosphate group.<\/p>\n

          The nucleotides are acids and are negatively charged at neutral pH. The carbons of pentose sugars are primed as 1′, 2′, 3′, to distinguish them from the carbons of nitrogenous bases. Nucleotides are joined together by phosphodiester linkage between 5′ and 3′ carbon atoms of pentose sugar. The chain of nucleic acid is abbreviated from 5′ end to 3′ end, in left to right order.<\/p>\n

                                                       \"\"<\/p>\n

                                       Fig.4. Structure of DNA.<\/p>\n

           <\/p>\n

                                  \"\"                      <\/p>\n

                                  Fig.5. Phosphodiester bond<\/p>\n

          The structure of DNA was first all worked out by James Watson and Francis Crick in 1953. To explain base equivalence (A \/ T, G \/ C) and other properties of DNA, Watson and Crick (1953), based on X-ray diffraction studies, proposed double helical structure of DNA. Watson and Crick model of DNA has following features-<\/p>\n

            \n
          • DNA is formed of two polynucleotide chains formed of deoxyribonucleotides.<\/li>\n
          • Presence of glycosidic bond and phosphodiester bond in the formation of DNA<\/li>\n
          • Two polypeptide chains of DNA are spirally coiled and form duplex, which has diameter of 20 angstrom<\/li>\n
          • Deoxyribose sugar and phosphoric acid forms the backbone of DNA and nitrogenous bases lies right angle to it.<\/li>\n
          • The polynucleotide chains show the polarity, one on each end of DNA strand has a free phosphate moiety at 5 ends called 5’ end and at the other end of the sugar has a free 3’-OH, called 3’end.<\/li>\n
          • Complementary base paring is present in DNA double helix between purine of one strand and pyrimidine of the second. These bonds connect 2-nucleotides. Between A & T there are 2 hydrogen bonds (A = T) and in between C & G there are 3 hydrogen bonds (C ≡ G). The C ≡ G base pair has more stability due to triple bond, as compared to the A = T base pair. The diameter of double helical structure of DNA is 2 nm (20 Å). Total distance from 1 base pair to another base pair (step or rise) = 0.34 nm (3.4 Å). Total base pairs in 1 complete turn (pitch) = 10 (in B-type DNA). The distance covered in 10 steps or 10 base pairs or 1 complete turn<\/li>\n
          • (Pitch) = 3.4 nm (34 Å). Based on number of base pairs and right or left handedness of helical the DNAs are of more than 12-forms<\/li>\n
          • Two strands of DNA are held together by the hydrogen bonds between their bases.<\/li>\n
          • Two strands of DNA duplex are parallel but are orients in the opposite direction, called antiparallel strands, means 5’ 3’<\/li>\n<\/ul>\n

              Solved examples<\/strong><\/p>\n

              Example 1.<\/strong> The repeating units in both DNA and RNA are called—–<\/p>\n

                             a) hydrogen bonds<\/p>\n

                             b) nucleic acids<\/p>\n

                             c)nucleotides<\/p>\n

                             d)amino acids<\/p>\n

               Solution 1<\/strong>: c. The repeating units in both DNA and RNA are called nucleotides<\/p>\n

              Example 2.<\/strong> What nucleotide base does RNA contain that DNA does not?<\/p>\n

                             a) adenine (A)<\/p>\n

                             b) cytosine (C)<\/p>\n

                             c)uracil (U)<\/p>\n

                             d)thymine (T)<\/p>\n

                Solution 2:<\/strong> c. Uracil is the nucleotide base does RNA contain that DNA does not.<\/p>\n

                                                       Summary <\/strong><\/p>\n

              \n
            • Nucleic acid is polymer of nucleotide and are of two types DNA and RNA<\/li>\n
            • DNA and RNA both act as genetic material but DNA is more stable and resists evolutionary changes and it is believed that DNA is formed from RNA after some modifications.<\/li>\n
            • RNA is mostly functions as catalyst and transfer expression of information.<\/li>\n
            • Complementary base paring is present in DNA double helix between purine of one strand and pyrimidine of second.<\/li>\n
            • These bonds connect 2 nucleotides. Between A and T, there are 2 hydrogen bonds and in between G and C there are 3 hydrogen bonds.<\/li>\n<\/ul>\n

               <\/p>\n

               <\/p>\n

               <\/p>\n","protected":false},"excerpt":{"rendered":"

              Unit: Chemistry of life Chapter: Nucleic acids Reference: Nucleic acids, Role of nucleic acids, The difference between DNA and RNA, Nucleotides  Learning objectives To understand the structure of nucleic acids Able to differentiate between DNA and RNA To understand the detailed structure of DNA Nucleic acids Nucleic acid are polymers of nucleotides and are of […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[629],"tags":[],"class_list":["post-9554","post","type-post","status-publish","format-standard","hentry","category-ap-biology"],"_links":{"self":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts\/9554","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/comments?post=9554"}],"version-history":[{"count":0,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/posts\/9554\/revisions"}],"wp:attachment":[{"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/media?parent=9554"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/categories?post=9554"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kapdec.com\/help\/wp-json\/wp\/v2\/tags?post=9554"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}