Question

List the five DNA condensation levels starting from the DNA double helix. Make sure to describe what the structure looks like, the size of each structure, and what proteins, if any, are involved.

Answer 1

Five levels of DNA condensation are-

1. DNA double helix- The diameter of the helix is 20 Å or 2 nm. This is the double helix structure of DNA where a DNA molecule consists of two strands that wind around each other like a twisted ladder.
2. Chromatin (DNA with histones) - At this level the DNA packages into nucleosomes that yields chromatin fibers. Chromatin is a complex of macromolecules which consists of DNA, protein (histones), and RNA. At this level DNA wraps around histone proteins forming nucleosomes, which gives it the "beads on a string" structure. The length of a chromatin fiber is 10 nm.
3. Chromatin during interphase with centromere - This is the third level in the condensation of DNA. At this level the chromatin is further condensed by coiling and now each coil contains about six nucleosomes. This structure of chromatin is known as solenoidal structure. The size of chromatin fiber now grows to 30 nm.
4. Two copies of condensed chromatin together during prophase – This is the fourth level of DNA condensation in which two copies of coiled chromatin are condensed together during prophase of cell cycle. This structure is also known as extended form of chromosome and condensed chromatin fibers now grow to 300 nm in diameter.
5. Chromosome during metaphase - This is the fifth and final level of DNA condensation, at this level the coil and condensed chromatin fibers are further condensed into chromosomes during metaphase stage of cell cycle. This structure is also known as condensed form of chromosome and is the size of 700 nm in diameter. Thanks!