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Describe the PACKAGING OF DNA HELIX IN A PROKARYOTIC AND EUKARYOTIC NUCLEUS
Carries 5 marks
Class 12 CBSE

Answer 1

Answer:

Explanation:

Prokaryotic cells can be distinguished from the eukaryotic cells by the presence of a well-defined nucleus. However, their negatively charged DNA is arranged in a region called the nucleoid. They appear as a loop wrapped around a protein molecule having a positive charge.

All eukaryotes have a well-defined nucleus that contains the DNA. DNA is a negatively charged polymer, packed compactly within the chromatin engirdling the histone proteins, a ball of positively charged proteins.

Histones are the proteins promoting the DNA packaging into chromatin fibres. Histone proteins are positively charged possessing several arginine and lysine amino acids binding to the negatively charged DNA.

The octamer of histone proteins is wrapped with DNA helix, giving rise to a structure called nucleosome. The nucleosomes are further coiled which results in the formation of chromatin fibres. Chromatin fibres are stained thread-like structures whereas nucleosomes are beads present over it. These chromatin fibres condense to form chromosomes during mitosis.

One of the benefits of DNA packaging is that it can be separated into things we use a lot and the things we don’t use at all. There are certain parts of DNA that are required only at certain times. Regions that are essential for the synthesis of proteins are loosely packed and are known as euchromatin. This helps the DNA to easily get in and make RNA. The heterochromatin has tightly packed DNA which are rarely required.

Answer 2

Answer:

prokaryotes:

negatively charged DNA is held with positively charged proteins in nucleoid DNA ine nucleoid is organised in in large loops held by protein

eukaryotes:

in nucleus the negatively charged DNA is wrapped around a positively charged histone octomer to form nucleosome. nucleosomes are repeated To constitute chromatin at higher level additional set of non histone chromosomal protein gets associated with chromatin.