Question

Describe the structure and packing of a eukaryotic chromosome.

Answer 1

The eukaryotic chromosome is a highly condensed form of structure in which the millions of DNA nucleotides have been carefully arranged. The order of packing and their complexity can be discussed as below:

1. The linear DNA is arranged in the form of nucleosomes in which a total of nearly 250 base pairs are wounded over an octamer of dimeric proteins. These octameric proteins wounded up by DNA are called nucleosomes. All nucleosomes are attached to each other by a linear chain of non-coding DNA called linker. This is called the beads-on-a-string model.
2. Next, the nucleosomal DNA gets wounded over itself giving rise to a nearly 30nm long fibre called a solenoid structure. This gives the shape of a telephone cord in structure.
3. These solenoid structures then arrange themselves in a group of 6 loop each giving rise to a nuclear scaffold.
4. Multiple nuclear scaffolds arrange themselves in a linear manner to get arranged compactly into a chromosomes in a linear manner.

Thus, in this way, a linear strand of DNA is condensed and wounded in a dense chromosome containing all the genetic information.This chromosome then contains other structures as well such as the centrosome at which the two arms of chromosomes are attached, the centromere at which the mitotic spindle fibre attaches, the terminal telomeres which prevent mutual sticking of chromosomes and maintain division and finally the DNA in the chromosome which contains whole genetic information.