Genetic Material Characteristics and Nature

What is Genetic Material?

The genetic material of any organism is the substance that stores information about the structure, function and development of various characteristics of a living organism. It is responsible for the transmission of genetic information for all the characteristics of living beings from parents to the progeny.

Following the rediscovery of Mendel’s laws, geneticists were able to conclude that organism’s characters are controlled by genes, that genes are able to reproduce themselves or replicate without losing their information, that genes are arranged on the chromosomes in a linear fashion, and that the genes are transmitted from parents to offsprings generation after generation almost unaltered.

Genetic Material Characteristics:

Based on the above conclusions, geneticists were able to assign the following characteristics to the genetic material-

(I) Storage of Genetic Information- It should have the ability to store all the genetic information about structure, function, development and reproduction in all the living cells of the organisms.

(II) Accurate Replication- It should possess the power of accurate replication so that the same genetic information as present in the parent cell is passed on to the daughter cells.

(III) Transcription- It should possess the power of accurate transcription so that the stored genetic information is transmitted to the cell as and when needed.

(IV) Chemical Stability- It should have physical and chemical stability so that the stored information is not lost.

(V) Variation- It should be capable of undergoing modifications by mutations and recombinations so that it can contribute to the variations and adaptations leading to the evolution of living organisms.

Genetic Material Nature:

After knowing that hereditary (genetic) material resides in the nucleus and that the chromatin material composing the genes is a complex of proteins and nucleic acids, the most important question to be solved was whether proteins form the genetic material or the nucleic acids.

Protein as the Hereditary Material:

Till the beginning of the 20th century, proteins were considered to be the only suitable material for storing and transmitting genetic information, because-

(I) Proteins have the required structural diversity necessary to perform the hereditary role and to store the hereditary information.

(II) Proteins are most abundant in the body, constituting about 16% of the total body weight.

(III) Proteins form the structural framework of the cell and are associated with the performance of all sorts of cellular and body activities and have a regulatory effect (functional diversity).

(IV) Proteins occur in varied forms (structural diversity). The possible combinations of 20 amino acids in proteins can be 20n, where ‘n’ is the number of amino acids in a polypeptide chain.

DNA or Nucleic Acid as Hereditary Material:

Though, known for long, DNA was not considered to be the possible genetic material. It was found to be a simple polymer of tetranucleotide sequences repeated over and over again. Therefore, DNA was thought to be too simple to form a gene. Rather, it was regarded to be a molecular framework or scaffold for the special proteins (genes) that carried genetic information.

Swiss biochemist, Johann Friedrich Miescher (1869), collected white blood cells from the pus from surgical bandages. By treating their nuclei with alkali, he prepared an extract and from that extract separated a nonprotein compound rich in phosphoric acid. Based on the source, this compound was named nuclein. It was largely formed of DNA. The quantitative analysis of chromosomes established that chromosomes are formed of 40 % DNA and 60 % of basic proteins or histones. The histones are small protein molecules rich in basic amino acids. They were named ‘protamines’.

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