Chapter 6: Molecular Basis of Inheritance

Ans: Bacteria changed their physical form throughout Griffith's experiment. The phrase for this was "transformation." The DNA of the $S$ strain bacteria survived the heating of bacteria in this experiment. The mice died of pneumonia after being injected with a mixture of deceased $S$ and $R$ strains. This demonstrated that DNA has the ability to survive harsh conditions and manifest itself when favorable conditions returned. For a material to be regarded as genetic material, it must be stable and long-lived. Thus, in Griffith's experiment, transformation aided in the identification of DNA as genetic material.

Ans: Experiments by Oswald Avery, Colin Macleod, and Maclyn McCarty (1933-44) revealed the biochemical nature of the transformative principle. The heat-killed $S$ cells were purified for biochemicals (proteins, DNA, and RNA). They were testing to determine which of them could change the $R$ strain. As a result, they discovered that whereas protein-digesting enzymes (proteases) and RNA-digesting enzymes (RNases) had no effect on transformation, DNase did. As a result, they came to the conclusion that it was the DNA that had the ability to change the R strain.

Ans: Meselson and Stahl used the heavy isotope of nitrogen in their experiment for a variety of reasons. Centrifugation in a Cesium chloride (CsCl) density gradient allowed the heavy DNA molecule (carrying $15 N$ ) to be easily separated from regular DNA. On the basis of density, it could be easily distinguished from lighter nitrogen (14N). The use of lighter and heavier nitrogen simplified the challenge of determining DNA transfer via successive generations.

Ans: A cistron is a piece of DNA that codes for a polypeptide. A cistron is a type of gene. Monocistronic refers to a stretch of replicating DNA that contains only one cistron (or gene), as seen in eukaryotes. Polycistronic refers to a stretch of replicating DNA that contains more than one cistron, as seen in bacteria and prokaryotes.

Ans: The human genome has six distinct characteristics:

• There are $3164.7$ million nucleotides in the human genome.

• In the human genome, the typical gene has 3000 bases. It is estimated that there are 30,000 genes in all. 

• Nucleotides are nearly identical in all humans (approximately $99.9 \%$ ). 

• Protein is coded for in less than $2 \%$ of the genome.

• Most genes (2968) are found on chromosome 1, whereas the fewest are found on chromosome Y. (231).

Ans: DNA replication is a tremendously energy-intensive process that necessitates a lot of it. As a result, the most practicable method is to copy DNA segments one by one. As a result, the full DNA molecule does not open at the same time.

The replication fork is a tiny opening in the DNA helix where DNA replication takes place. A replication fork is a name for this opening.

NTPs (nucleotide triphosphates) are monomers that contain a nucleotide bonded to three phosphates. The NTPs found in DNA are referred to as dNTPs. They are the fundamental components of life. They play a crucial part in a variety of metabolic processes.

Ans: The core dogma in molecular biology was proposed by Francis and Crick. Genetic information goes from DNA through RNA to Protein, according to this theory. Genetic information travels in the reverse direction in retroviruses, i.e., Protein RNA DNA. As a result, retroviruses are considered to defy fundamental dogma. Retroviruses use a technique known as reverse transcription since the steps are performed in the opposite order.

Ans: By calculating the distance between two successive base pairs by the total number of base pairs, the length of the DNA double helix may be computed.

\[0.44 \times 10^{-9} \mathrm{~m} \times 2 \times 10^{9} \mathrm{bp}\] \[=0.88 \mathrm{~m}\]

Ans: Acidic amino acids include aspartic and glutamic acid, while basic amino acids include lysine and arginine. Aspartic acid and glutamic acid have negative charges on their side chains, whereas lysine and arginine have positive charges on their side chains. The negative charge of DNA wraps around the positive charge of the histone octamer. DNA will not be able to wrap around itself if acidic amino acids are present in histone due to mutation. As a result, a long strand of DNA will be unable to fit into the nucleus's limited space. This will signal the end of nuclear power, which is made possible by effective packing.

Ans: Because RNA is less durable than DNA, DNA has supplanted RNA as the genetic material in living organisms. Heat would have destroyed RNA if it had been the genetic material in Griffith's experiment. As a result, the heat-killed Pneumococcus strain could not have turned the R-strain into a virulent strain.