DNA and Genetics

• DNA replication goes in the 5' to 3' direction because DNA polymerase acts on the 3'-oh of the existing strand for adding free nucleotides.
• Histones are rich in the basic amino acid residues lysines and arginines and forms histone octamer.
• Catalytic converters, having expensive metals namely platinum-palladium and rhodium as the catalysts, are fitted into automobiles for reducing the emission of poisonous gases.
• As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water, and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas, respectively.
• Fermentation of idli or dosa batter is carried out largely by lactic acid bacteria, the same class of microorganisms that are found in ‘curd.’
  
• So the correct answer is " Template with 5′⟶3′ polarity shows continuous DNA replication ".

DNA replication, is the process of producing two identical replicas from one original DNA molecule. This biological process, occurs in all living organisms and forms the basis for biological inheritance. DNA is made up of two strands and each strand of the original DNA molecule serves as a template for the production of the complementary strand, a process referred to as semiconservative replication.

DNA replication requires both DNA polymerase (for synthesis) and DNA ligase (for joining fragments).

Helicase is the enzyme responsible for unwinding the DNA double helix by breaking the hydrogen bonds between complementary base pairs. Other enzymes like DNA polymerase and ligase are involved in synthesis and repair, while topoisomerase relieves supercoiling.

Ligase joins DNA fragments (correct). Helicase breaks hydrogen bonds (correct). DNA polymerase synthesizes DNA by adding nucleotides, it does not cut DNA at specific sites (that is the function of restriction endonucleases).

DNA polymerase cannot initiate synthesis de novo; it requires a short RNA primer synthesized by DNA primase to provide a free 3'-OH group.

Topoisomerases are enzymes that manage DNA supercoiling by cutting one or both strands of the DNA backbone to relieve torsional strain.

Plasmid DNA can be analysed using agarose gel electrophoresis. When sample of DNA is loaded, onto the agarose gel and electric field is applied, it results in separation of DNA molecules according to their size and shape. On agarose gel, small molecules of DNA are able to pass easily in the electric field. DNA possesses strong negative charge which helps in its movement towards positive electrode in the electrophoresis apparatus. Along with size and shape of DNA molecule, electrophoresis buffer type also determines the rate of migration of DNA molecule.

  E. coli , a gram negative rod shaped bacteria has since the time of discovery have been commonly used for biological lab experiment and research. The simple cell structured E. coli has one circular chromosome and a ds circular DNA molecule with 4.6 million base pairs in length and 4288 protein coding genes.

Pili are minute hair like appendages, that emerges from suface of Gram -ve bacteria. They have similar structure as flagella and often involved in attachment to surface and making of biofilm. They also help in DNA exchange. They are involved in conjugation which results in transfer or exchange of genetic material. 

Escherichia coli is a rod-shaped, gram-negative bacterium that is typically 1-3 micrometers in length.

Agrobacterium radiobacter strain K84 is used for the biological control of crown gall disease. It produces a bacteriocin called agrocin 84, which inhibits the growth of pathogenic Agrobacterium tumefaciens.

Glycocalyx is the outermost layer of the cell envelope. Cell wall lies between plasma membrane and glycocalyx.

Gram staining differentiates bacteria based on the structure and composition of their cell wall, specifically the thickness of the peptidoglycan layer.