Molecular Basis of Inheritance Test 5

Meselson and Stahl prove experimentally semi conservation of DNA replication not say but structure of DNA.

Avery, MacLeod and Mcarty conclude DNA is heridatary material first time while Griffith show transforming principal.

Transformation was discovered in Streptococcus pneumoniae in 1928 by Frederick Griffith; in 1944, Oswald T. Avery, Colin M. MacLeod, and Maclyn McCarty demonstrated that the “transforming principle” was DNA. Both results are milestones in the elucidation of the molecular nature of genes.

Nucleobases, also known as nitrogenous bases  are nitrogen-containing biological compounds that form nucleosides, which in turn are components of nucleotides, with all of these monomersconstituting the basic building blocks of nucleic acids. The ability of nucleobases to form base pairs and to stack one upon another leads directly to long-chain helical structures such as ribonucleic acid (RNA) and deoxyribonucleic acid (DNA)....

According to Chargaff’s rule in all cellular DNA, regardless of the species, number of adenosine residues is equal to the number of thymidine residues which means that A = T and the number of guanosine residues is equal to the number of cytidine residues; G = C . Hence, that the sum of the purine residues equals the sum of the pyrimidine residues; i.e., A + G = T + C.

In Hershey and Chase experiment, some bacteriophage viruses where grown in a medium which contained radioactive phosphorus(32P) and some in radioactive sulphur(35S) medium. Viruses grown under radioactive (32P) contained radioactive DNA and Viruses grown under radioactive (35S) contained radioactive protein. When infected in E.coli separately, bacterial cells were gently agitated in blender to remove viralcoats from the bacteria. Culture was also centrifuged. Radioactive 32P was found to be associated with the bacterial cell whereas Radioactive 35S was found in the surrounding medium. Hence, the process resulted in viral DNA. 

Nucleotides are organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA. The building blocks of nucleic acids, nucleotides are composed of a nitrogenous base, a five-carbon sugar and at least one phosphate group.

mRNA carries genetic information from DNA to ribosomes for synthesising polypeptide chains. tRNA carries amino acids to mRNA for translation. rRNA is a vital component of ribosomes.

 In the DNA of an organism a total number of 5386 nucleotides were found out of which the proportion of different bases were: Adenine = 29%, Guanine = 17%, Cytosine = 32%, Thymine = 17%. Considering the Chargaff’s rule it can be concluded that it is a single stranded DNA.

Beadle and Tatum proposed their one gene one enzyme hypothesis on the basis of biochemical genetics in Neurospora crassa. Beadle and Tatum showed that each kind of mutant bread mould lacke a specific enzyme. Their experiments demonstrated that genes carry information for making proteins.

Nucleosomes can be said when the DNA is wrapped around the histone protein, so this structure is called nucleosome and it has 200 base pairs of the DNA helix.

5-bromo uracil (Bu) is base analogue of thymine. Transitions are caused by base analogues.