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Which one of the following also acts as a catalyst in a bacterial cell?

  • sn RNA

  • hn RNA

  • 23 S rRNA

  • 23 S rRNA


C.

23 S rRNA

23 SrRNA in bacteria is the enzyme ribozyme for the formation of a peptide bond. 23 S rRNA is found large sub- unit (70 S) of ribosome of bacteria.

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The unequivocal proof of DNA as the genetic material came from the studies on a 

  • bacterium

  • fungus

  • viroid

  • viroid


D.

viroid

The unequivocal (leaving no doubt; unambiguous) proof that DNA is the genetic material came from the experiments of Alfred Hershey and Martha chase. They worked with viruses that infect bacteria called bacteriophages.

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Silencing of mRNA has been used in producing transgenic plants resistant to

  • bollworms

  • nematodes

  • White rusts

  • White rusts


B.

nematodes

RNA interference (RNAi) takes place in all eukaryotic organisms as a method of cellular defence. This method involves silencing of a specific mRNA due to a complementary ds RNA molecule that binds to an prevents translation of the mRNA (silencing). The source of the complementary RNA could be from an infection by viruses having RNA genome of mobile genetic elements (transposons) that replicate via an RNA intermediate. Using Agrobacterium vectors, nematode -specific genes were introduced into the host plant. The introduction of DNA was such t hat it produced both sense and anti -sense RNA in the host cells. These two RNA's being complementary to each other formed a dsRNA that initiated RNAi and thus, silenced the specific mRNA of the nematode. The result was that the parasite could not survive in a transgenic host expressing specific interfering RNA. The transgenic plant, therefore, got itself protected from the parasite. 

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What are those structures that appear as 'beads-on-string' in the chromosomes when viewed under electron microscope?

  • Nucleotides

  • Nucleosomes

  • Base pairs

  • Base pairs


B.

Nucleosomes

Nucleosome is sub-microscopic sub-unit of chromatin which is formed by wrapping of DNA over a core of histone proteins. The term was coined by Oudet et. al, (1975). It is oblate structure with a length of 10 nm and a thickness of 5-5.7 nm. Its core is called nu-body. The latter is formed of four pairs of histone molecules - H2A, H2B, H3 and H4. DNA makes 1.75 turns over the octamer to form a nucleosome. Two adjacent nucleosomes are connected by a short segment of unbound DNA called linker DNA. A fifth type of histone called H1 is attached over the linker DNA. Nucleosomes appear as 'beads-on-string' in the chromosomes under electron microscope.

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The process of RNA interference has been used in the development of plants resistant to 

  • fungi

  • viruses

  • insects

  • insects


D.

insects

The process of RNA interference (RNA) has been used in the development of plants resistant to nematodes like Molodegyne incognitia, which infects the roots of tobacoo plants and causes a great reduction in yied. RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (sliencing).

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