Question

How are chromosomes related to chromatin?

Answer 1

Hint: Chromosomes are dense thread-like structures located inside the nucleus of animal and plant cells. Chromatin fibres are complex DNA and protein found in nucleus eukaryotic cells.

Complete answer:
DNA packaging is an important phenomenon in eukaryotic cells. DNA needs to be coiled and supercoiled in various forms. This is done with the help of histone proteins which provides structural support to DNA forms. Complexes of histone proteins and linker DNA form nucleosomes which gives the chromosome a more compact shape. There are five major types of histones— H1, H2A, H2B, H3, and H4. Some variants of histones are associated with the regulation of gene expression.

Chromosomes are densely compact structures present in the nucleus during cell division. Each species have a definite number of chromosome pairs. Chromosomes have a central part called centrosome which binds to spindle fibres during cell division. The chromatin fibres combine, condense and supercoil during cell division to form chromosomes. When chromatids are seen under electron microscope they have a beaded appearance, with the beads spaced at intervals of approximately 200 base pairs. Chromosomes also pair us as sister chromatids during cell division. The chromosomes are in nanometer range.

Chromatin fibers are long and thin. They are uncoiled structures found inside the nucleus. Chromosomes are compact, thick and thread-like. These are coiled structures seen prominently during cell division. Chromatin is a densely packed condensed network of DNA and proteins found in the nucleus. Chromatin is composed of DNA, RNA and protein. The proteins present in chromatin are of two types: histones and nonhistones. The primary function of chromatin is packaging long DNA molecules into more compact, denser structures. The compact packaging prevents the DNA strands from entanglement and also plays important roles during cell division, preventing DNA damage, regulation of gene expression and DNA replication.

Note: Several structures are seen in DNA packaging. These structures are nucleosome, chromosomes, solenoid, 300 nm structure, chromatid and chromosomes. The two types of chromatin are- Euchromatin and Heterochromatin.