REPLICATION:

The replication is the process of formation of identical copies of duplex of using parental DNA as its template (aka coding strand). It is an autocatalytic function. It occurs during the S phase of cellular division in eukaryotes. DNA replication was semi- conservative, which means one of its parental strands is conserved in the progeny's DNA. It was discovered by James Watson and Crick in the year 1953. 

EXPERIMENTAL PROOF FOR SEMICONSERVATIONE

Meselson and F.W Stahel experiment. 

The grown Escherichia coli in a medium containing heavy isotope of Nitrogen N (15) in the form of NH4Cl. The generation time of E. coli is 20 minutes. The DNA was isolated from the cells of each generation and the DNA was tested for the heavy isotope of Nitrogen through density gradient centrifugation using cesium chloride which is water soluble and heavy salt. It was centrifuged at high speed, 500000  rpm for many hours. A fluorescent chemical pigment is added to enhance the contrast as it is specific to DNA. 

TATA BOX

It is also known as Goldberg - Hogness Box. the short nucleotide sequence 20-30 base pair at 5' of initiation site of eukaryotic and archaea genes to which RNA polymerase two binds. The consensus sequence is TATA AAA.

TATAAT BOX

It is also known as Pribnow - Schaller box. it is a six nucleotide occurs in bacteria at - 10 of initiation site

TRANSCRIPTION

The process of formation of RNA by a template of DNA is called transcription. it forms a single stranded RNA which has base sequence complementary to template strand. But similar to sense or coding strand of DNA strand which functions as a template for RNA synthesis is called templates or non-coding or plus strand or non sense strand. 

GENE

 The term gene was coined by Johanssen to replace Mendelian factor used by Correns.  T.H morgan defined it as a part of chromosome which functions as a unit of recombination.Gene is also considered as a unit that can undergo mutation. Beadle and Tatum defined gene as unit of hereditary material that specifies a  single enzyme in their famous one gene one enzyme. Later Yanofsky and others modified  it as  one gene one polypeptide hypothesis. After Watson and Crick proposed DNA as the genetic material S. Benzer related gene as a cistron or segment of DNA that codes for one polypeptide chain, one t-rna  and r-rna  or any other function- one gene - one function.