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 :
  - DNA is associated with protamines, proteins more basic than histones. It is found in sperm .