Nucleic acids are the only molecules in nature that can guide their own reproduction from monomers. Indeed, the likeness of kids to their parents is based on precise DNA replication and transfer from generation to generation.

DNA contains hereditary information that guides the development of your biochemical, anatomical, physiological, and, to a lesser degree, behavioral characteristics.

Frederick Griffith conducted research on two strains of the bacteria Streptococcus pneumonia. The S (smooth) strain can cause pneumonia in mice; it is harmful because the cells have an exterior capsule that protects them from the immune system of the animal.

R (rough) strain cells lack a capsule and are hence nonpathogenic. Griffith inoculated mice with the following strains to test for pathogenicity:

The live R bacteria had been converted into dangerous S bacteria by an unknown, heritable chemical derived from the dead S cells, which allowed the R cells to produce capsules.

T. H. Morgan's group demonstrated that genes exist as chromosomal components, and the two chemical components of chromosomes—DNA and protein—emerged as the main candidates for genetic material.

Until the 1940s, the evidence for proteins appeared to be stronger: biochemists had discovered proteins as a type of macromolecules with high variability and function specialization, both of which were required for hereditary material. Furthermore, nothing was understood about nucleic acids, whose physical and chemical characteristics appeared to be far too consistent.

This viewpoint progressively shifted when the significance of DNA in inheritance was discovered in studies of bacteria and the viruses that infect them, considerably simpler systems than fruit flies or humans.

In 1928, a British medical officer called Frederick Griffith began working on developing a pneumonia vaccine. He was researching Streptococcus pneumonia, a bacteria that causes mammalian pneumonia.

Griffith possessed two strains (varieties) of the bacteria, one pathogenic (producing illness) and one nonpathogenic (harmless). He was somewhat aback to see that when he eliminated the harmful germs.

Furthermore, the altered bacteria's newly acquired pathogenicity was passed along to all of their progeny. This heritable alteration was apparently produced by a chemical component of the dead pathogenic cells, however, the identification of the molecule was unknown.

Griffith named the phenomena transformation, which is currently defined as a shift in genotype and phenotype caused by a cell's absorption of foreign DNA. Oswald Avery, Maclyn McCarty, and Colin MacLeod later recognized the changing material like DNA.

The image attached demonstrates a virus infecting a bacterial cell. A phage called T2 attaches to a host cell and injects its genetic material through the plasma membrane, while the head and tail parts remain on the outer bacterial surface (colorized TEM).

Studies of viruses that infect bacteria provided more proof that DNA was the genetic material (as shown in the image attached). These viruses are known as bacteriophages (which means "bacteria-eaters"), or phages for short. Viruses are far less complex than cells.

A virus is nothing more than DNA (or, in some cases, RNA) encased in a protective coat, which is frequently just protein. A virus must enter a cell and take over the cell's metabolic system in order to reproduce new viruses.

Phages have been frequently utilized as tools by molecular genetics researchers. Alfred Hershey and Martha Chase performed in 1952.

They utilized a radioactive isotope of sulfur to tag protein in one batch of T2 and a radioactive isotope of phosphorus to target DNA in the other. Because protein includes sulfur but not DNA, radioactive sulfur atoms were exclusively absorbed into the phage's protein. Similarly, radioactive phosphorus atoms tagged just the DNA, not the protein, because the phage's DNA contains virtually all of its phosphorus. Separate samples of nonradioactive E. coli cells were infected with the protein-labeled and DNA-labeled batches of T2 in the experiment. The researchers next examined the two samples immediately after the infection began to determine which sort of molecule—protein—was present.

Each DNA nucleotide monomer is made up of a nitrogenous base (T, A, C, or G), deoxyribose (blue), and a phosphate group (yellow).

A covalent link connects the phosphate group of one nucleotide to the sugar group of the next, producing a "backbone" of alternating phosphates and sugars from which the bases protrude. A polynucleotide strand is directed from the 5′ end (with the phosphate group) to the 3′ end (with the sugar's OH group). The numerals 5′ and 3′ relate to the carbons in the sugar ring.

These two discoveries came to be known as Chargaff's rules: The makeup of DNA bases differs between species, and the percentages of A and T bases, as well as those of G and C bases, are nearly equal for each species.