Long Answer TypeHow did Hershey and Chase established that DNA is transferred from virus to bacteria?
Short Answer TypeName the enzyme and state its property that is responsible for continuous and discontinuous replication of the two strands of a DNA molecule.
Why is the enzyme cellulase needed for isolating genetic material from plant cells and not from the animal cells?
Describe the structure of a RNA polynucleotide chain having four different types of nucleotides.
Draw a schematic diagram of a part of double stranded dinucleotide DNA chain having all the four nitrogenous bases and showing the correct polarity.Â
It is established that RNA is the first genetic material. Explain giving three reasons.
(a) Name the enzyme responsible for the transcription of tRNA and the amino acid the initiator tRNA gets linked with.
(b) Explain the role of initiator tRNA in initiation of protein synthesis.
Long Answer TypeState the aim and describe Messelson and Stahl experiment.
Messelson and Stahl in 1958 performed and experiment to prove that the DNA replicates in a semi-conservative fashion.
Experimental proof
(1) They grew E.coli in a medium containing 15NH4Cl (15N is the heavy isotope of nitrogen) as the only nitrogen source for many generations. As a result, 15N was incorporated into
the newly-synthesized DNA. This heavy DNA could be distinguished from the normal by centrifugations in CsCl (cesium chloride) density gradient.
(2) Then, they transferred the E. coli cells to a medium with normal 14NH4Cl and the DNA samples were extracted at various time intervals. The DNA samples taken were double-stranded helix. The various samples were separated on the basis of CsCl gradients for measuring the density of DNA.
(3) Since E.coli divides in 20 min, they extracted DNA from the culture one generation after the transfer from N15 to N14 medium after 20 min. After 40 minutes, the DNA of the second generation was extracted from the 14NH4Cl medium and was found to have equal amounts of hybrid and light DNA. Thus it was proved that DNA replication is semiconservative since the samples contained both N15 and N14 strands that is both hybrid and light.
Short Answer Type
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