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Structure of DNA

DNA (deoxyribonucleic acid) is the genetic blueprint of all living organisms, containing the instructions for physiological traits. Its structure is a double-helix formed by two anti-parallel strands of repeating sugar and phosphate backbones, linked by nitrogenous bases (adenine, thymine, cytosine, and guanine) bonded through hydrogen bonds. Each complete turn of the helix occurs every 10 bases, revealing its characteristic shape. Wrapped around histones, DNA condenses into chromatin, facilitating its organization and expression within cells.

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Structure of DNA

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  1. Structure of DNA

  2. All organisms have a genetic code • DNA (deoxyribonucleic acid) contains the genetic code, and is the blueprint for the expression of physiological traits • Each individual organism has its own unique blueprint

  3. The DNA structure is a double-stranded helical shape, twisted around a common axis • The width is 20 Å (angstroms) • Normally, the DNA strand can be found wrapped around specialized proteins called histones. When it not wrapped, the double-helical shape is more evident

  4. The two backbones are comprised of repeating sugarand phosphate molecules • Each backbone is linked to the other via nitrogenous bases connected by hydrogen bonds • The right-handed helix makes a complete turn every 10 bases and 3.4 nm

  5. The two backbones are anti-parallel—one strand running 5’ (prime) to 3’, the other from 3’ to 5’

  6. The “rungs” of the double-helical ladder are comprised of four nitrogenous bases (adenine, thymine, cytosine, and guanine) • Each base pair is held together by a hydrogen bond • A binds with T, and C binds with G (Chargaff’s rule)

  7. The pentose sugar and phosphate group comprise the backbone • Each sugar-phosphate group is bonded to the next by a covalent phosphodiester bond • Each phosphate connects the 5’ carbon of one nucleotide to the 3’ carbon of another • The nitrogenous bases is bound to the pentose sugar

  8. There are two classes of nitrogenous bases: pyrimidinesand purines • Cytosine and thymine are pyrimidines, a one-ring structure • Adenine and guanine are purines, a two-ring structure

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