• To get to the conclusion that DNA followed a semi-conservative mode of replication, Meselson and Stahl grew E.coli in 15NH4Cl for many generations to get 15N incorporated into DNA.
• Then the cells were transferred into 14NH4Cl.
• The extracted DNA were centrifuged in CsCl and measured to get their densities.
• DNA extracted from the culture after one generation, 20 minutes showed intermediate hybrid density.
• DNA extracted after two generations, 40 minutes showed light DNA and hybrid DNA.
Mechanism of translation in prokaryotes:
• First, charging of tRNA occurs by aminoacylation.
• Small subunit of ribosome binds to the 5’ end of the mRNA
• For initiation, the ribosome binds to the mRNA at the start codon (AUG) that is recognised only by initiator tRNA,
• In the elongation phase amino acid with tRNA sequentially bind to the appropriate codon on mRNA (forming complimentary base pairs with tRNA anticodon.)
• Ribosome moves from codon to codon along the mRNA and amino acids are added one by one in the two sites of the large subunit joined by peptide bond.
• Termination occurs when a release factor binds to the stop codon and releases the complete polypeptide.
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