The search for genetic material - class-XII

Gel electrophoresis separates DNA fragments based on their size/molecular weight through an agarose or polyacrylamide gel matrix when an electric current is applied, allowing analysis of fragment lengths.

70S ribosomes, chromatophores, and circular DNA are characteristic features of prokaryotes, but they are not found in all prokaryotes. For instance, non-photosynthetic prokaryotes lack chromatophores, making these features present only in some prokaryotes.

In the B-DNA double helix model, one full turn of the helix spans 3.4 nanometers and contains 10 base pairs.

The Griffith effect refers to the discovery of bacterial transformation, where non-virulent bacteria were converted into virulent ones by a 'transforming principle' from dead virulent bacteria.

In Streptococcus pneumoniae, the virulent strain possesses a polysaccharide capsule that makes the colonies appear smooth (S-strain), while the non-virulent strain lacks a capsule and appears rough (R-strain).

Frederick Griffith first demonstrated bacterial transformation in 1928 using Streptococcus pneumoniae.

The genetic code is a set of rules by which information encoded in genetic material is translated into proteins by living cells, specifically determining the sequence of amino acids.

The genetic code is a triplet code, meaning a sequence of three nucleotides (a codon) specifies a single amino acid.

The operon model for gene regulation in prokaryotes was proposed by François Jacob and Jacques Monod in 1961.

RNA polymerase binds to the promoter region of an operon to initiate the transcription of the structural genes.

The central dogma of molecular biology describes the flow of genetic information: DNA is transcribed into mRNA, which is then translated into a polypeptide chain using tRNA and amino acids.

Frederick Griffith conducted the first transformation experiments in 1928, providing the foundation for identifying DNA as the genetic material.

In the Hershey-Chase experiment, the bacteriophage injects its DNA into the bacterium while the protein coat remains outside. Since the bacterium becomes radioactive, it confirms that the DNA, which carries the radioactive label, was successfully transferred into the host.

Frederick Griffith's experiment with Streptococcus pneumoniae demonstrated that a 'transforming principle' could change non-virulent bacteria into virulent ones, which was later identified as DNA.

Beadle and Tatum studied nutritional mutants in the bread mold Neurospora crassa. Their work led to the 'one gene, one enzyme' hypothesis, stating that each gene is responsible for the synthesis of a specific enzyme.

Electroporation is a technique where an electrical field is applied to cells to increase the permeability of the cell membrane, allowing DNA to be introduced into the plant cell.

Frederick Griffith is correctly credited with the discovery of bacterial transformation in 1928. The other options contain historical inaccuracies regarding the scientists or their specific contributions.

The three stop (terminator) codons are UAA, UAG, and UGA. All of these begin with the nucleotide Uracil (U).

Transposons, often called jumping genes, are DNA sequences that can change their position within a genome.

Statement 1 is correct because the genetic code is degenerate (multiple codons for one amino acid). Statement 3 is correct because the genetic code is nearly universal. Statement 2 is false because some amino acids like methionine have only one codon. Statement 4 is false because bacteria use the same codon system.

Statement 1 is correct because Frederick Griffith discovered bacterial transformation in Streptococcus pneumoniae. Statement 2 is correct because George Gamow proposed that the genetic code consists of a combination of three nucleotides (triplet code). Statement 3 is incorrect because Meselson, along with Stahl, proved semi-conservative DNA replication, whereas isolation of DNA was done by Friedrich Miescher.

The genetic code is nearly universal, and UUU is the codon that codes for phenylalanine in almost all organisms.

In the bacterial ribosome, the 23S rRNA is a ribozyme, meaning it acts as a catalyst (specifically, a peptidyl transferase) to form peptide bonds between amino acids during translation.

Transformation is the process by which bacteria take up naked DNA from their environment, as demonstrated by Griffith's experiment with S and R strains of Streptococcus pneumoniae.

Statement ii is correct (definition of transformation) and iv is correct (Griffith's discovery). Statement i refers to conjugation, and iii is historically incorrect as transformation was not the basis for the chromosomal theory of inheritance.

Genetic material must be stable to store information accurately over generations. If it were unstable, it could not reliably pass on traits.

In semi-conservative replication, after one generation, all DNA is hybrid. After two generations, half the DNA is hybrid and half is light (14N-14N). Starting with one 15N-15N molecule, after two generations, you have four molecules: two hybrid (15N-14N) and two light (14N-14N).

DNA and RNA can be detected using photometric procedures (like UV absorbance), staining reactions (like Feulgen stain for DNA), and enzyme digestion (using DNase or RNase to confirm identity).