Question

Semi conservative replication of DNA was first demonstrated in
A. Streptococcus pneumoniae
B. Salmonella typhimurium
C. Drosophila melanogaster
D. Escherichia coli

Answer 1

Hint: Bacteria which is anaerobic and commonly found in the lower intestine of warm-blooded organisms.

Complete answer:
The cells which are commonly known were found to undergo the semiconservative replication mechanism of DNA replication. This mechanism was first demonstrated and observed in Escherichia coli. Escherichia coli is also called E. Coli is a bacteria whose strains are harmless, but some may cause serious food poisoning.

Additional information
- DNA replication occurs on multiple origins of replication along the DNA template strand.
- As the DNA helix is unwound by helicase, replication occurs separately on each template strand in antiparallel directions. This process is semiconservative replication because two copies of the original DNA molecule are produced.
- Each molecule of the DNA consists of two strands, one of the strands is the original one while the other strand is the newly-synthesized one.
- For semiconservative to occur, the DNA helix needs to be separated so the new template strand can be bound to the complementary base pairs.
- Topoisomerase is the enzyme that aids in the unzipping and recombination of the double helix.
- Semiconservative replication provides many advantages for DNA, it is fast, accurate, and allows for easy repair of DNA.

So, the correct answer is ‘Escherichia coli’.

Note: The double helix structure of DNA was proposed by Watson and Crick in 1953. Nikolai Koltsov was the first to anticipate the semiconservative model of the DNA and this model was later by Meselson-Stahl in their experiment. They confirmed that DNA replicated semi conservatively by conducting an experiment using two radioisotopes: nitrogen-15 (15N) and nitrogen-14 (14N).