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5.2.1.3. Tertiary structure of DNA

Tertiary structure of DNA

The tertiary structure is the arrangement that the double-stranded DNA fiber adopts as it associates with proteins to form chromosomes. The tertiary structure varies depending on whether it is prokaryotic or eukaryotic organisms:

  • In prokaryotes, DNA folds like a superhelix , generally in a circular shape and associated with a small amount of proteins. The same occurs in cellular organelles such as  mitochondria and in chloroplasts.
  • In eukaryotes, given that the amount of DNA in each chromosome is very large, the packaging has to be more complex and compact; This requires the presence of proteins, such as histones and other proteins of a non-histonic nature (in sperm these proteins are protamines).

Fundamental ideas about the tertiary structure of DNA

Tertiary structure of DNA

  • In prokaryotic cells: supercoiled DNA.
  • In eukaryotic cells:
    • Nucleosomal fiber or pearl necklace.
      • The chromatin  comprises DNA is associated with histones.
      • Nucleosome sequence (histone octamers), particles about 100 Å = 10 nm in diameter. The nucleosome is made up of:
        • The nucleus or core is made up of:
          • An octamer of histones .
          • About 146 nitrogenous base pairs of DNA that are arranged around the octamer.
        • Spacer or linker DNA is the DNA between two consecutive nuclei. It is doublestranded DNA of approximately  200 pairs of nucleobases. Nucleosomes are made up of:
    • Crystal structure :