Question

DNA packaging in eukaryotes​

Answer 1

Answer:

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DNA packaging in eukaryotes_??

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In eukaryotes, this organisation is much more complex and is carried out by a set of positively charged basic proteins called histones. Histones are rich in the basic amino acids residues lysines and arginines with charged side chains. There are five types of histone proteins i.e., H₁, H.A, H₂B, H, and H. Four of them occur in pairs to produce histone octamer or nu-body (two copies of each H.A, H₂B, H, & H). The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome.

Answer 2

The DNA is an organic, complex, molecular structure, found in both prokaryotic and eukaryotic cells and also in many viruses. It is a hereditary material that is found in the nucleus of the cell and is mainly involved in carrying genetic information.

The DNA structure has the following characteristics:

• The strands of the DNA are helically wounded, every single strand forms a right-handed coil.
• The pitch of each helix is 3.32 nm and about 10 nucleotides make up one turn.
• The distance between two succeeding base pairs is 0.34 nm
• The total length of a DNA is the distance between two succeeding base pairs and the product of a total number of base pairs.
• A typical DNA has an extent around 2.2 meters, which is much longer than a nucleus.

Prokaryotic cells can be distinguished from 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 DNA. DNA is a negatively charged polymer, packed compactly within the chromatin engirdling the histone proteins, a ball of positively charged proteins.

The octamer of histone proteins is wrapped with a DNA helix, giving rise to a structure called a 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 them. These chromatin fibres condense to form chromosomes during mitosis.