Question

What is DNA packaging? Describe the importance of it.

Answer 1

Hint: During DNA packaging, DNA is wrapped around histones. Histones are proteins that allow DNA to be tightly packaged into units called nucleosomes. Each nucleosome is composed of DNA that is wound 1.65 times around eight histone proteins, namely 2 H2A, 2 H2B, 2 H3, and 2 H4.

Complete answer:
A large amount of DNA is tightly packed in the small nucleus of every cell by DNA packaging. Three levels of DNA packaging have been recognized, primary, secondary, and tertiary. The primary organization of chromatin involves the coiling of DNA at regular intervals around a histone pool to form a series of particles called nucleosomes. Thus, the primary organization results in a beaded polynucleotide chain. Nucleosome core particle consists of eight histone molecules, known as core histones, and a small DNA segment called core DNA. The core histones include two molecules each of H2A, H2B, H3, and H4. The secondary organization is represented by the coiling of a polynucleotide chain in a solenoid manner to form a hollow fiber. The tertiary organization is attained by the radial looping of the solenoid fiber from an axial scaffold. Each of them contains 20,000 to 10,000 base pairs. DNA packaging helps the DNA to fit well within the small size of a cell. It also facilitates the easy separation of the correct chromosomes during cell division. Due to highly packed DNA, it is easy to turn genes on or off as per requirement.

Additional Information: -The nucleosomal organization of chromatin is an ingenious packaging mechanism by which chromosomal DNA is densely packed and tightly condensed to the lowest level in such a way that it’s specific regions remain fully accessible for highly regulated expression.
-Nucleosomes serve as a first-order packaging mechanism for the shortening of eukaryotic DNA.
-The solenoid arrangement of nucleosomes brings about extreme condensation and compaction of chromatin filaments.

Note: -Nucleosomes play a major role in controlling gene expression by lowering the rate of genetic transcription.
-In most cases, they cover promoter sequence and repress transcription.
-DNA with nucleosomes has a much lower rate of transcription than those without nucleosomes.