GENETIC MATERIAL(Replication, Transcription, Translation) 1st part........

Genetic material governs the inheritance of traits from one generation to the next as well as it is able to express its effects through the formation and functioning of the traits. It stores biological information in the coded form.

The genetic material should have the following characteristics : 1. It should be able to precisely duplicate

itself, forming its carbon copies. This

is called replication. 2. It should be able to faithfully pass its

copies into the progeny. 3. It should be able to occasionally undergo

mutations to allow adaptation and

evolution to occur in the organism. 4. It should be able to store information

in the coded form for the control of

biological functions of the cells. 5. It should be able to express its

information in the progeny. In addition to all these characteristics, genetic material should be present in every cell and it should show diversity.

There was a lot of controversy about the nature of genetic material. Earlier proteins were considered as the genetic material because of their structural complexity and lot of diversity. Because proteins lack the mechanism of duplication, they do not qualify to act as genetic material.

DNA-The Genetic Material

DNA carries most of the characteristics listed above, so it can act as genetic material, Moreover, now it has been experimentally proved that DNA is the genetic material.

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Experiment of Griffith About Bacterial Transformation

Frederick Griffith (1928), a British Medical officer found that there are two strains of Diplococcus pneumoniae pneumonia causing bacterium, one that forms smooth colonies (S-strain

virulent strain) protected by a thick sheath of mucilage, called capsule and another that forms irregular or rough colonies (R-strain or non virulent strain) which is without a capsule when grown on a suitable medium in petridishes. When injected into (Fig. 30.1) mice (A), only capsulated smooth cells (virulent) produced the disease, but not the non-virulent cells (B). On the other hand heat killed virulent cells (C) did not cause the disease but when heat killed capsulated (Virulent) cells were mixed with non-virulent rough cells (D) and then were injected into the mice, the disease was caused. From the blood of infected mice, live S-cells could be isolated. Thus, some factor from the heat killed S-cells converted the live R-cells into live capsulated or S-cells which caused the disease.

Avery, McCarty and MacLeod in 1944 gave the molecular explanation for the experiment of Griffith. They separated the extract from smooth virulent bacteria intoseparately into separate groups of mice. They that non-virulent

R-bacteria containing only DNA fraction got transformed into virulent or S-strain bacteria, whereas there was no change in others. Thus, DNA isolated from heat killed virulent cells, when added to rough cells changed their surface character from rough to smooth and also made them virulent. This phenomenon ofDNA, protein and polysaccharide fractions. Each fraction was added separately into separate culture medium containing non-virulent or R bacteria and were injectedtransferring characters of one strain to another by using DNA extract is called transformation. When this DNA extract was treated with enzyme DNAase (DNA hydrolysing enzyme), DNA inactivated and incapable of transforming R-strain into S-strain. The transforming property was lost when same DNA extract was treated with proteases (protein hydrolysing enzyme), the transforming property was not lost.