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Structure of Chromosome

Grade 8
Aug 22, 2022


The cell is the basic unit of living organisms. From bacteria to humans, all are made up of cells, which contain a nucleus and the nucleus contains DNA. 


DNA (Deoxy Ribo Nucleic Acid) passes characteristics from one generation to another. It is the blueprint for a living thing and codes for proteins. It is a spiral chain-like molecule made up of 4 different types of nucleotides. ( A, T, C and G.)  


Chromosomes are the entire chain of DNA and proteins. Each chromosome is made up of DNA and proteins.  

Chromosomes are thread-like in appearance and are located inside the nucleus of animal and plant cells. 

Discovery of chromosomes  

The chromosome was first discovered by Walther Flemming. He called the thread-like structure present in the nucleus as chromatin in 1878. Karl Nageli observed the rod shape of chromosomes in the plant cell in 1842. 


A chromosome is an entire chain of DNA along with a group of proteins. Chromosomes is thread-like in appearance and are located inside the nucleus of animal and plant cells. Each chromosome is made up of proteins and DNA.   

The thread-like structure of the chromosome is the chromatin fibre. This chromatin fibre is a collection of protein molecules called histones. If we zoom in on the string, we can find there is a chain of DNA in it, which is extremely long with millions of nucleotides and contains hundreds of genes along its length.  

Chromosome Structure 

Chromosomes are made of 50% proteins, and 50% DNA (deoxyribonucleic acid). Chromosomes are made of many chromatin threads, each containing DNA and proteins. 

There are 23 pairs of chromosomes in the human genome, making it 46 altogether. 

The main parts of chromosomes are: 

Centromere, Chromatid, Chromatin Telomere. 



  • Sister chromatids are joined by the centromere. 
  • Spindle fibres during the cell division are attached at the centromere 
  • It helps in the movement of the chromosome during a stage called the anaphase during cell division. 


  • Each chromosome has two symmetrical structures called chromatids or sister chromatids, which is visible in mitotic metaphase. 
  • Each chromatid contains a single DNA molecule 
  • At the anaphase of the mitotic cell division, sister chromatids separate and migrate to opposite poles. 


Chromatin is made up of DNA, RNA and proteins. At interphase, chromosomes are visible as the thin chromatin fibres present in the nucleoplasm. During cell division, the chromatin fibres condense and chromosomes are visible. 


 The terminal part of a chromosome is known as the telomere. Telomeres are polar, which prevents the fusion of chromosomal segments. 

Functions of chromosomes  

DNA present on the chromosome not only carries most of the genetic information but also controls the hereditary transfer. 

  • Chromosomes are essential for the process of cell division, replication, division, and creation of daughter cells. 
  • Chromosomes are often called the ‘packaging material’ because it tightly holds the DNA and proteins together in the eukaryotic cells. 


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