Difference Between Chromatin Fiber and Chromosome

Key Difference – Chromatin Fiber vs Chromosome
 

Eukaryotic organisms have a nucleus in their cells and true organelles covered with membranes. The genome of these organisms is located inside the nucleus. The human genome is composed of a total of 46 chromosomes in 23 homologous pairs. The total length of the DNA is packaged within these 46 chromosomes in a cell. During DNA packaging, DNA form complexes with positively charged proteins and exist as stable structures called chromatin fibers. Chromatin fibers collectively make the chromosomes. Chromatin fiber can be defined as a fiber composed of DNA and histone protein complexes. A chromosome can be defined as a thread like structure composed of chromatin fibers. This is the key difference between chromatin and chromosomes.

CONTENTS

1. Overview and Key Difference
2. What is a Chromatin Fiber
3. What is a Chromosome
4. Similarities Between Chromatin Fiber and Chromosome
5. Side by Side Comparison – Chromatin Fiber vs Chromosome in Tabular Form
6. Summary

What is a Chromatin Fiber?

Chromatin is the complex of DNA and proteins. The basic unitof the chromatin is nucleosome. The nucleosome is composed of a segment of DNA wrapped around a core histone protein. The core protein is an octomer that is made from eight histone proteins. A DNA fragment winds 1.65 times around the eight histone proteins.

Nucleosomes appear as beads in a string. Nucleosomes fold many times and form the 30 nm chromatin fiber. Chromatin fibers compress and fold to produce wider chromatin fibers. Chromatin fibers coil tightly into chromatids of a chromosome. Chromatin appears as a diffuse mass of genetic material during the initial stage of the cell division.

What is a Chromosome?

A chromosome is a thread like structure composed of nucleic acids and proteins that contain the genetic information of the eukaryotic organisms. Chromosomes are arranged within the nucleus. They carry complete genetic information of an organism in the form of genes. Genes are the repositories of the information to synthesize proteins. The packaging of chromosomal DNA inside the nucleus is supported by histone proteins. Histone proteins provide energy and space for winding DNA. Hence, histones are spool-like proteins which aid the nicely packaging of DNA into chromatin fibers. The human genome is composed of 23 homologous chromosome pairs. Among the 23 pairs, 22 pairs are considered as autosomal chromosomes while one pair is sex chromosomes.

The number of chromosomes and the size of chromosomes differ among the living organisms. Bacteria possess one or two circular chromosomes while most of the eukaryotic organisms have linear chromosomes. Prokaryotic chromosomes are not enclosed by a nuclear membrane, unlike eukaryotic chromosomes.

Cell division is a process in which new daughter cells are produced. During the cell division, chromosomes uncoil to facilitate the beginning of DNA synthesis. Chromosomes are not visible in normal cells. However, during the cell division, they start to appear as a diffuse mass of chromatin fibers initially and then as separate chromosomes during the prophase and metaphase of the cell division. Then DNA replicates and produces a new set of chromosomes for the newly synthesized cells.

What are the Similarities Between Chromatin Fiber and Chromosome?

• Chromatin and chromosomes possess DNA and proteins.
• Both Chromatin Fiber and Chromosome are made up of tightly packaged DNA.
• Both Chromatin Fiber and Chromosome structures are extremely important for living organisms.

What is the Difference Between Chromatin Fiber and Chromosome?

Summary – Chromatin Fiber vs Chromosome 

Chromosomes are thread-like structures in which DNA molecules are packaged. They are the repositories of the genetic information of an organism. The number of chromosomes and their shapes are differing among the living organisms. A human cell contains 46 chromosomes, which are in 23 homologous pairs. Prokaryotes possess less number of chromosomes which are not enclosed by a nuclear membrane. Chromosome has four chromatids and a centromere region. Chromosomes are not visible in normal cells. They become visible during the cell division under the microscope. Chromosomal DNA exists as chromatin fibers. Chromatin fibers are the complexes of DNA and histone proteins. The basic unit of the chromatin is nucleosome and nucleosomes are composed of a segment of DNA wrapped around eight histone proteins. Nucleosomes coil into loops and form tightly compacted chromatin fibers. Chromatin fibers coil tightly and form chromatids and chromatids form chromosomes. This is how DNA is packaged inside a small space of nucleus within a cell. This is the difference between chromatin and chromosome.

Reference:

1.Nature News, Nature Publishing Group. Available here  
2.The Editors of Encyclopædia Britannica. “Chromosome.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 15 Jan. 2018. Available here  

Image Courtesy:

1.’Nucleus & Chromatin Territorial Structure’ (CC BY-SA 2.5) via Commons Wikimedia
2.’Figure 10 01 03’By CNX OpenStax  (CC BY 4.0) via Commons Wikimedia