The Search for Genetic Material Questions in English

(D) The central dogma of molecular biology,proposed by $F.H.C.$ Crick in $1958$,describes the unidirectional flow of genetic information from $DNA$ to $mRNA$ and then to protein.
However,$H.$ Temin and $D.$ Baltimore discovered that in certain retroviruses,such as $HIV$,genetic information can flow from $RNA$ to $DNA$.
This process is known as reverse transcription or Teminism.
It is catalyzed by the enzyme reverse transcriptase.
Therefore,$HIV$ does not follow the standard central dogma of molecular biology.

(A) Avery,MacLeod,and McCarty purified biochemicals (proteins,$DNA$,$RNA$,etc.) from the heat-killed $S$ cells to see which ones could transform live $R$ cells into $S$ cells.
They discovered that $DNA$ alone from $S$ bacteria caused $R$ bacteria to become transformed.
They also used specific enzymes to digest these molecules:
$1$. Proteases (which digest proteins) did not affect transformation.
$2$. RNases (which digest $RNA$) did not affect transformation.
$3$. DNase (which digests $DNA$) inhibited transformation.
Therefore,they concluded that $DNA$ is the hereditary material.

(D) The Hershey-Chase experiment,conducted in $1952$ by Alfred Hershey and Martha Chase,proved that $DNA$ is the genetic material.
The experiment involved three main steps:
$1$. Infection: Bacteriophages were allowed to infect $E. coli$ bacteria.
$2$. Blending: The viral coats were removed from the bacteria by agitating them in a blender.
$3$. Centrifugation: The virus-infected bacteria were separated from the lighter viral particles using a centrifuge.
$PCR$ (Polymerase Chain Reaction) is a technique used to amplify $DNA$ segments and was not part of the Hershey-Chase experiment.

(D) molecule that acts as genetic material must fulfill the following criteria:
$1$. It should be able to generate its replica (replication).
$2$. It should be chemically and structurally stable.
$3$. It should provide the scope for slow changes (mutation) that are required for evolution.
$4$. It should be able to express itself in the form of Mendelian characters.
Heat resistance is not a mandatory requirement for a molecule to act as genetic material. Therefore,the statement 'It should be heat resistant' is not correct.

(A) Frederick Griffith performed a series of experiments in $1928$ using the bacterium $Streptococcus \text{ } pneumoniae$ (also known as $Pneumococcus$).
He used two strains of this bacterium: $S$-strain (virulent, smooth, encapsulated) and $R$-strain (non-virulent, rough, non-encapsulated).
Through his experiments on mice, he observed the phenomenon of bacterial transformation, where the $R$-strain bacteria were transformed into $S$-strain bacteria by a 'transforming principle' released from heat-killed $S$-strain bacteria.
Therefore, the correct organism used in his experiments was $Pneumococcus$.

(D) For a molecule to act as genetic material,it must fulfill certain criteria:
$1$. It should be able to generate its replica ($DNA$ replication).
$2$. It should be chemically and structurally stable.
$3$. It should provide the scope for slow changes (mutation) that are required for evolution.
$4$. It should be able to express itself in the form of Mendelian characters.
Since $DNA$ satisfies all these criteria,it is the primary genetic material in most organisms.

(C) The provided image illustrates the Hershey-Chase experiment,which was conducted to prove that $DNA$ is the genetic material.
In this experiment,bacteriophages (viruses that infect bacteria) were used.
The diagram shows the process of infection where the bacteriophage attaches to the bacterial cell surface and injects its genetic material $(DNA)$ into the host cell.
The protein coat (capsid) remains outside the bacterial cell.
Therefore,the experiment demonstrates the entry of viral genetic material into the bacteria.

(A) In most organisms,$DNA$ acts as the genetic material,while $RNA$ primarily functions as a messenger.
However,in certain viruses,$RNA$ serves as the genetic material.
$TMV$ (Tobacco Mosaic Virus) is a well-known example of a virus where the genetic material is $RNA$.
Cyanobacteria,Cladophora,and Sieve cells are cellular organisms that contain $DNA$ as their genetic material.

(A) For a molecule to act as a genetic material,it must fulfill several criteria:
$1$. It should be able to generate its replica (replication).
$2$. It should be chemically and structurally stable.
$3$. It should provide the scope for slow changes (mutation) that are required for evolution.
$4$. It should be able to express itself in the form of Mendelian characters.
Option $A$ correctly identifies the requirement for mutation,while options $B$ and $C$ contradict the necessary criteria for a genetic material. Therefore,the correct characteristic is that it must allow for mutation.

(B) During the isolation of $DNA$ from a cell,various impurities such as $RNA$,proteins,and lipids must be removed to obtain pure $DNA$.
$1$. $RNA$ is removed by treating the mixture with the enzyme $Ribonuclease$ $(RNase)$,which degrades $RNA$.
$2$. Proteins are removed by treating the mixture with the enzyme $Protease$,which breaks down proteins into amino acids.
Therefore,the correct sequence of enzymes is $Ribonuclease$ and $Protease$.

(B) Oswald Avery,Colin MacLeod,and Maclyn McCarty worked to determine the biochemical nature of the 'transforming principle' in Griffith's experiment.
They purified biochemicals (proteins,$DNA$,$RNA$,etc.) from the heat-killed $S$ strain of Streptococcus pneumoniae.
They discovered that $DNA$ alone from the heat-killed $S$ strain caused the transformation of non-virulent $R$ strain bacteria into virulent $S$ strain bacteria.
They also observed that protein-digesting enzymes (proteases) and $RNA$-digesting enzymes (RNases) did not affect transformation,whereas $DNA$-digesting enzymes (DNases) inhibited the process.
Thus,they concluded that the genetic material is $DNA$.

(D) Alfred Hershey and Martha Chase $(1952)$ conducted experiments using bacteriophages. They grew some phages in a medium containing radioactive phosphorus $(^{32}P)$ to label $DNA$ and others in a medium containing radioactive sulfur $(^{35}S)$ to label proteins. They allowed these phages to infect $E. coli$ bacteria. After agitation and centrifugation,they observed that radioactive phosphorus $(^{32}P)$ was found inside the bacterial cells,while radioactive sulfur $(^{35}S)$ remained in the supernatant. This proved that $DNA$,not protein,entered the bacteria and acted as the genetic material.

(A) The pneumococcus experiment,famously known as Griffith's transformation experiment,demonstrated that a 'transforming principle' from heat-killed virulent $S$-strain bacteria could transform non-virulent $R$-strain bacteria into virulent $S$-strain bacteria. Later,Avery,MacLeod,and McCarty identified this 'transforming principle' as $DNA$. This experiment provided the first strong evidence that $DNA$ is the genetic material.

(C) Frederick Griffith discovered the phenomenon of transformation in $1928$ while working with $Streptococcus$ $\text{pneumoniae}$.
He observed that heat-killed virulent bacteria could transform live non-virulent bacteria into virulent ones.
This experiment provided the first evidence that there is a 'transforming principle' capable of changing the genetic characteristics of an organism.

(NONE) The criteria for a molecule to act as genetic material are as follows:
$1$. It should be able to generate its replica (replication).
$2$. It should be stable chemically and structurally.
$3$. It should provide the scope for slow changes (mutation) that are required for evolution.
$4$. It should be able to express itself in the form of Mendelian characters.
All the given options are standard criteria for genetic material. However,in the context of this question,if we look for an exception,all options provided are actually correct criteria. If the question implies which is $NOT$ a criterion,all are valid. Given the standard nature of this question,it is often asked to identify the correct criteria. Since all are correct,the question is technically flawed as an '$EXCEPT$' question. Assuming the question asks for the criteria,all are correct.

(B) The unequivocal proof that $DNA$ is the genetic material came from the experiments of Alfred Hershey and Martha Chase $(1952)$.
They worked with bacteriophages,which are viruses that infect bacteria.
They grew some viruses on a medium that contained radioactive phosphorus $(^{32}P)$ and some on a medium that contained radioactive sulfur $(^{35}S)$.
Viruses grown in the presence of radioactive phosphorus contained radioactive $DNA$ but not radioactive protein because $DNA$ contains phosphorus but protein does not.
Similarly,viruses grown on radioactive sulfur contained radioactive protein but not radioactive $DNA$ because $DNA$ does not contain sulfur.
When these radioactive phages were allowed to infect $E. coli$ bacteria,it was observed that only the radioactive phosphorus $(^{32}P)$ entered the bacterial cells,indicating that $DNA$ is the genetic material that is transferred from the virus to the bacteria.

(C) Alfred Hershey and Martha Chase $(1952)$ conducted experiments using bacteriophages that infect $E. coli$ bacteria.
They grew some viruses in a medium containing radioactive phosphorus $(^{32}P)$ to label $DNA$ and others in a medium containing radioactive sulfur $(^{35}S)$ to label proteins.
After allowing the viruses to infect the bacteria,they used a blender to separate the viral coats from the bacterial cells and then centrifuged the mixture.
They observed that radioactive phosphorus $(^{32}P)$ was found inside the bacterial cells,while radioactive sulfur $(^{35}S)$ remained in the supernatant (viral coats).
This proved that $DNA$ is the genetic material that enters the bacteria,not the protein.

(N/A) Hershey and Chase worked with bacteriophages and $E. coli$ to prove that $DNA$ is the genetic material. They used different radioactive isotopes to label the $DNA$ and the protein coat of the bacteriophage.
They grew some bacteriophages on a medium containing radioactive phosphorus $(^{32}P)$ to label the $DNA$ and some on a medium containing radioactive sulphur $(^{35}S)$ to label the protein.
Then,these radioactively labelled phages were allowed to infect $E. coli$ bacteria. After infection,the protein coat of the bacteriophage was separated from the bacterial cell by blending and then subjected to the process of centrifugation.
Since the protein coat was lighter,it was found in the supernatant,while the infected bacteria settled at the bottom of the centrifuge tube.
It was observed that radioactive $(^{32}P)$ was present in the bacterial cells,while radioactive $(^{35}S)$ was found in the supernatant. Hence,it was proved that $DNA$ is the genetic material as it was transferred from the virus to the bacteria.

(N/A) Offspring exhibit traits similar to their parents. Most organisms originate from a zygote formed by the fusion of male and female gametes.
Initially,there was no clarity regarding the material responsible for genetic traits.
Mendel described these genetic materials as 'factors'. About a hundred years later,it was understood that this genetic material exists in the form of chromosomes.
Chromosomes primarily consist of nucleoproteins. Nucleoproteins have two components: $(1)$ Nucleic acids and $(2)$ Proteins.
Modern research in molecular biology has proven that the nucleic acid present in chromosomes is responsible for the transmission of hereditary traits.
Two types of nucleic acids are found in biological systems,namely Deoxyribonucleic acid $(DNA)$ and Ribonucleic acid $(RNA)$.
In most organisms,$DNA$ acts as the genetic material,but in some viruses,$RNA$ serves as the genetic material.
$RNA$ mostly functions as a messenger. $RNA$ also performs other functions; it acts as an adapter,a structural molecule,and in some cases,as a catalytic molecule.

(N/A) Based on the earlier discoveries of Gregor Mendel,Sutton,Morgan,and other scientists,it was clear that chromosomes in the nucleus carry genetic information,but the nature of the genetic material remained unclear.
The search for the mechanism of genetic inheritance reached the molecular level by $1926$.
In $1928$,Frederick Griffith performed a series of experiments with Streptococcus pneumoniae (pneumococcus) bacteria.
When Streptococcus pneumoniae bacteria are grown on a culture plate,some produce smooth,shiny colonies ($S$ strain),while others produce rough colonies ($R$ strain). This is because $S$ strain bacteria have a mucous (polysaccharide) coat,whereas $R$ strain bacteria do not. When mice were infected with the $S$ strain (virulent),they died from pneumonia infection. However,when mice were infected with the $R$ strain,they did not develop pneumonia.
$S$ strain $\longrightarrow$ Injection into mice $\longrightarrow$ Mice died.
$R$ strain $\longrightarrow$ Injection into mice $\longrightarrow$ Mice lived.
Griffith killed the bacteria by heating them. He observed that injecting heat-killed $S$ strain bacteria into mice did not cause death. When he injected a mixture of heat-killed $S$ strain and live $R$ strain into mice,the mice died. Furthermore,he recovered live $S$ bacteria from these dead mice.
$S$ strain (heat-killed) $\longrightarrow$ Injection into mice $\longrightarrow$ Mice lived.
$S$ strain (heat-killed) $+$ $R$ strain (live) $\longrightarrow$ Injection into mice $\longrightarrow$ Mice died.
Griffith concluded that the $R$ strain bacteria were transformed by the heat-killed $S$ strain bacteria.
Transformation Principle: Some transforming principle transferred from the heat-killed $S$ strain to the $R$ strain,causing the $R$ strain to develop a smooth polysaccharide coat,which made it virulent. This suggested that the genetic material itself had been transformed.

(N/A) Before the work of Avery,MacLeod,and McCarty $(1944)$,it was believed that protein was the genetic material.
These scientists worked to determine the biochemical nature of the 'transforming principle' observed in Griffith's experiment.
They purified biochemicals ($DNA, RNA,$ and proteins) from heat-killed $S$ cells to see which one could transform live $R$ cells into $S$ cells.
They discovered that $DNA$ from the $S$ bacteria was the only substance that caused the transformation of $R$ bacteria.
They observed that digestion with protein-digesting enzymes (proteases) or $RNA$-digesting enzymes $(RNases)$ did not affect the transformation,proving that the transforming substance was neither protein nor $RNA$.
However,digestion with $DNase$ inhibited the transformation process. This confirmed that $DNA$ is the genetic material responsible for transformation.

(N/A) The proof that $DNA$ is the genetic material came from the experiments of Alfred Hershey and Martha Chase $(1952)$. They worked on viruses that infect bacteria,called bacteriophages.
Bacteriophages attach to bacteria and inject their genetic material into the host cell. The bacteria then treat the viral genetic material as if it were its own and subsequently manufacture more virus particles.
Hershey and Chase conducted experiments to determine whether it was $DNA$ or protein that entered the bacteria from the virus.
They grew some viruses in a medium containing radioactive phosphorus $(^{32}P)$ and others in a medium containing radioactive sulfur $(^{35}S)$. Viruses grown in the presence of radioactive phosphorus contained radioactive $DNA$ but not radioactive protein because $DNA$ contains phosphorus,while proteins do not.
Similarly,viruses grown in radioactive sulfur contained radioactive protein but not radioactive $DNA$ because $DNA$ does not contain sulfur.
These radioactive bacteriophages were then allowed to infect $E. coli$ bacteria. As the infection proceeded,the viral coats were removed from the bacteria by agitating them in a blender. The virus particles were then separated from the bacteria by spinning them in a centrifuge. The bacteria that were infected with viruses that had radioactive $DNA$ were radioactive,indicating that $DNA$ was the material that passed from the virus to the bacteria. Bacteria that were infected with viruses that had radioactive proteins were not radioactive,indicating that protein did not enter the bacteria.

(N/A) molecule must fulfill the following criteria to act as a genetic material:
$(i)$ It should be able to generate its replica (replication).
$(ii)$ It should be chemically and structurally stable.
$(iii)$ It should provide the scope for slow changes (mutation) that are required for evolution.
$(iv)$ It should be able to express itself in the form of 'Mendelian characters'.
If one examines the criteria of base pairing and complementarity,it is evident that both nucleic acids ($DNA$ and $RNA$) have the ability to direct their duplications. Other molecules in the living system,such as proteins,fail to fulfill these criteria.

(N/A) $1.$ Transformation: The phenomenon in which the genetic characteristics of an organism are altered due to the incorporation of foreign genetic material $(DNA)$ is known as transformation.
$2.$ Messenger $\text{RNA}$ $(m\text{RNA})$: It carries the genetic information transcribed from $DNA$ to the site of protein synthesis (ribosomes) to direct the assembly of amino acids.

(N/A) $1.$ Friedrich Miescher identified $DNA$ as an acidic substance present in the nucleus in $1869$. He named it 'Nuclein'.
$2.$ Maurice Wilkins and Rosalind Franklin produced the $X$-ray diffraction data for $DNA$, which was crucial for understanding its structure.

(N/A) Francis Crick proposed the Central Dogma in molecular biology, which states that genetic information flows from $DNA \rightarrow RNA \rightarrow \text{Protein}$.
Frederick Griffith, in his experiment with $Streptococcus \text{ } pneumoniae$, concluded that the $R$-strain bacteria had been 'transformed' by the heat-killed $S$-strain bacteria. He suggested that some 'transforming principle' was transferred from the heat-killed $S$-strain to the $R$-strain, enabling the $R$-strain to synthesize a smooth polysaccharide coat and become virulent.

(A) In $1928$,Frederick Griffith,in a series of experiments with $Streptococcus$ $pneumoniae$ (the bacterium responsible for pneumonia),witnessed a miraculous transformation in the bacteria. During his experiment,a living organism (bacteria) changed its physical form.
When $Streptococcus$ $pneumoniae$ bacteria are grown on a culture plate,some produce smooth shiny colonies $(S)$ while others produce rough colonies $(R)$.
This is because the $S$ strain bacteria have a mucous (polysaccharide) coat,while the $R$ strain does not. Mice infected with the $S$ strain (virulent) die from pneumonia,but mice infected with the $R$ strain do not.
$S$ strain $\rightarrow$ Inject into mice $\rightarrow$ Mice die
$R$ strain $\rightarrow$ Inject into mice $\rightarrow$ Mice live
Griffith killed the bacteria by heating them. He observed that heat-killed $S$ strain bacteria injected into mice did not kill them.
$S$ strain (heat-killed) $\rightarrow$ Inject into mice $\rightarrow$ Mice live
When he injected a mixture of heat-killed $S$ and live $R$ bacteria,the mice died. Moreover,he recovered living $S$ bacteria from the dead mice.
$S$ strain (heat-killed) $+$ $R$ strain (live) $\rightarrow$ Inject into mice $\rightarrow$ Mice die
He concluded that the $R$ strain bacteria had been transformed by the heat-killed $S$ strain bacteria. Some 'transforming principle',transferred from the heat-killed $S$ strain,enabled the $R$ strain to synthesize a smooth polysaccharide coat and become virulent. This indicated the transfer of genetic material,although the biochemical nature of this material was not defined by his experiments.

(N/A) Oswald Avery,Colin MacLeod,and Maclyn McCarty ($1933$-$1944$) worked to determine the biochemical nature of the 'transforming principle' in Griffith's experiment.
They purified biochemicals such as proteins,$DNA$,and $RNA$ from heat-killed $S$ cells to observe which of these could transform live $R$ cells into $S$ cells.
They discovered that $DNA$ alone from $S$ bacteria caused $R$ bacteria to become transformed.
They also discovered that protein-digesting enzymes (proteases) and $RNA$-digesting enzymes $(RNases)$ did not affect transformation,indicating that the transforming substance was neither a protein nor $RNA$.
Digestion with $DNase$ inhibited the transformation,confirming that $DNA$ was the molecule responsible for the transformation.
They concluded that $DNA$ is the hereditary material,although not all biologists were convinced at that time.

(N/A) The genetic material of a retrovirus is $RNA$.
At the time of protein synthesis, the $RNA$ is first 'reverse transcribed' into its complementary $DNA$ using the enzyme reverse transcriptase.
This process is the reverse of the flow of information described in the central dogma $(DNA \rightarrow RNA \rightarrow \text{Protein})$.
Therefore, retroviruses are not considered to follow the central dogma.

(N/A) $RNA$ is chemically more labile and prone to degradation compared to $DNA$ due to the presence of the $2'-OH$ group in its ribose sugar.
Furthermore,$RNA$ is highly susceptible to enzymatic degradation by ribonucleases,which are ubiquitous in the environment.
Therefore,if $RNA$ were the genetic material,the heat-killed $S$-strain would likely have been degraded during the experimental process and would not have retained its ability to transform the $R$-strain into a virulent form.

(B) The use of $^{15}N$ is inappropriate because the detection methods for $^{32}P$ and $^{15}N$ differ. $^{32}P$ is a radioactive isotope,whereas $^{15}N$ is a stable,heavier isotope of nitrogen,not a radioactive one.
Even if $^{15}N$ were radioactive,it would not provide conclusive results because nitrogen is a fundamental component of both $DNA$ (in nitrogenous bases) and proteins (in the amino groups of amino acids).
Therefore,if $^{15}N$ were used,it would be detected in both the bacterial cell pellet and the supernatant,making it impossible to distinguish whether the genetic material transferred was $DNA$ or protein.

(N/A) The unequivocal proof that $DNA$ is the genetic material came from the experiments of Alfred Hershey and Martha Chase $(1952)$. They worked with viruses that infect bacteria,called bacteriophages.
$1$. Experimental Setup: They grew some viruses on a medium containing radioactive phosphorus $(^{32}P)$ and others on a medium containing radioactive sulfur $(^{35}S)$. Since $DNA$ contains phosphorus but not sulfur,viruses grown in radioactive phosphorus had radioactive $DNA$. Conversely,since proteins contain sulfur but not phosphorus,viruses grown in radioactive sulfur had radioactive proteins.
$2$. Infection and Blending: These radioactive phages were allowed to infect $E. coli$ bacteria. After infection,the viral coats were removed from the bacterial surface by agitating them in a blender.
$3$. Centrifugation: The virus particles were separated from the bacteria by spinning them in a centrifuge. The heavier bacterial cells formed a pellet,while the lighter viral coats remained in the supernatant.
$4$. Conclusion: Bacteria infected with viruses containing radioactive $DNA$ $(^{32}P)$ were found to be radioactive,whereas bacteria infected with viruses containing radioactive proteins $(^{35}S)$ were not. This conclusively proved that $DNA$,not protein,is the genetic material that enters the bacteria.
$5$. Hypothetical Scenario: If both $DNA$ and proteins contained both phosphorus and sulfur,the experiment would not have been able to distinguish between the two. The radioactivity would have been present in both the pellet and the supernatant regardless of which molecule entered the cell,making it impossible to conclude which one was the genetic material.

(A) molecule that acts as genetic material must fulfill the following criteria:
$(i)$ Ability to replicate: Due to base pairing and complementarity,both $DNA$ and $RNA$ can direct their own duplication. Proteins fail to meet this criterion.
$(ii)$ Chemical and structural stability: Genetic material must remain stable across different life stages,ages,and physiological changes. $DNA$ is more stable than $RNA$ because the $2'-OH$ group present in every nucleotide of $RNA$ makes it reactive and easily degradable. Additionally,$RNA$ is catalytic,whereas $DNA$ is less reactive. The presence of thymine instead of uracil in $DNA$ also provides additional stability.
$(iii)$ Scope for slow mutation: Both $DNA$ and $RNA$ can mutate. $RNA$ is unstable and mutates at a faster rate,which is beneficial for viruses with short life spans but less ideal for long-term storage of genetic information.
$(iv)$ Expression as Mendelian characters: $RNA$ can directly code for protein synthesis,while $DNA$ depends on $RNA$. However,because $DNA$ is more stable,it is preferred for the storage of genetic information,while $RNA$ is better suited for the transmission of information and protein synthesis. Thus,$DNA$ evolved from $RNA$ with chemical modifications to enhance stability.

(N/A) molecule must fulfill the following criteria to act as a genetic material:
$(i)$ It should be able to generate its replica (replication).
$(ii)$ It should be chemically and structurally stable.
$(iii)$ It should provide the scope for slow changes (mutation) that are required for evolution.
$(iv)$ It should be able to express itself in the form of 'Mendelian characters'.
If one examines each requirement one by one,because of the rule of base pairing and complementarity,both nucleic acids ($DNA$ and $RNA$) have the ability to direct their duplications. Other molecules in the living system,such as proteins,fail to fulfill these criteria.

(N/A) Genetic material is the substance that carries biological information from one generation to the next.
At the time of Mendel,the nature of 'factors' regulating the pattern of inheritance was not clear.
Over the next hundred years,the nature of the putative genetic material was investigated,culminating in the realization that $DNA$ (deoxyribonucleic acid) is the primary genetic material.
Nucleic acids are polymers of nucleotides.
$DNA$ and $RNA$ (ribonucleic acid) are the two types of nucleic acids found in living systems.
$DNA$ acts as the genetic material in most organisms.
$RNA$,although it acts as genetic material in some viruses,mostly functions as a messenger $(mRNA)$.
$RNA$ also has additional roles,functioning as an adapter $(tRNA)$,a structural component $(rRNA)$,and in some cases,as a catalytic molecule (ribozyme).

(N/A) Following are the criteria that a molecule must fulfill to act as a genetic material:
$(i)$ It should be able to replicate itself.
$(ii)$ It should be stable both chemically and structurally.
$(iii)$ It should provide the scope for slow changes (mutation) which are required for evolution.
$(iv)$ It should be able to express itself in the form of 'Mendelian Characters'.
According to these criteria,both $DNA$ and $RNA$ have the ability to direct their duplication (because of the rule of base pairing) and complementarity using specific processes,whereas other molecules in the living system fail to fulfill the first criterion itself,e.g.,proteins.

(N/A) Although the discovery of nuclein by Meischer and the proposition of the principles of inheritance by Mendel occurred around the same time,it took a long time to discover and prove that $DNA$ acts as the genetic material.
By $1926$,the quest to determine the mechanism for genetic inheritance had reached the molecular level.
Previous discoveries by Gregor Mendel,Walter Sutton,Thomas Hunt Morgan,and numerous other scientists had narrowed the search to the chromosomes located in the nucleus of most cells.
Transforming Principle: In $1928$,Frederick Griffith,in a series of experiments with $Streptococcus$ $pneumoniae$ (the bacterium responsible for pneumonia),witnessed a miraculous transformation in the bacteria.
During his experiment,a living organism (bacteria) changed its physical form. When $Streptococcus$ $pneumoniae$ bacteria are grown on a culture plate,some produce smooth,shiny colonies $(S)$ while others produce rough colonies $(R)$.
This is because the $S$ strain bacteria have a mucous (polysaccharide) coat,while the $R$ strain does not.
Mice infected with the $S$ strain (virulent) die from pneumonia,but mice infected with the $R$ strain do not develop pneumonia.
$S$ strain $\longrightarrow$ Inject into mice $\longrightarrow$ mice die
$R$ strain $\longrightarrow$ Inject into mice $\longrightarrow$ mice live
Griffith was able to kill bacteria by heating them.
He observed that heat-killed $S$ strain bacteria injected into mice did not kill them.
$S$ strain (heat-killed) $\longrightarrow$ Inject into mice $\longrightarrow$ mice live
$S$ strain (heat-killed) $+ R$ strain (live) $\longrightarrow$ Inject into mice $\longrightarrow$ mice die
When he injected a mixture of heat-killed $S$ and live $R$ bacteria,the mice died. Moreover,he recovered living $S$ bacteria from the dead mice.
He concluded that the $R$ strain bacteria had somehow been transformed by the heat-killed $S$ strain bacteria. Some 'transforming principle' transferred from the heat-killed $S$ strain enabled the $R$ strain to synthesize a smooth polysaccharide coat and become virulent.
This must be due to the transfer of the genetic material. However,the biochemical nature of the genetic material was not defined by his experiments.

(A) Even though the discovery of nuclein by Meischer and the proposition for principles of inheritance by Mendel were almost at the same time,the fact that $DNA$ acts as a genetic material took a long time to be discovered and proven.
By $1926$,the quest to determine the mechanism for genetic inheritance had reached the molecular level.
Previous discoveries by Gregor Mendel,Walter Sutton,Thomas Hunt Morgan,and numerous other scientists had narrowed the search to the chromosomes located in the nucleus of most cells.
$1$. Transforming Principle: In $1928$,Frederick Griffith,in a series of experiments with $Streptococcus$ $pneumoniae$ (bacterium responsible for pneumonia),witnessed a miraculous transformation in the bacteria.
During the course of his experiment,a living organism (bacteria) changed in physical form. When $Streptococcus$ $pneumoniae$ bacteria are grown on a culture plate,some produce smooth shiny colonies $(S)$ while others produce rough colonies $(R)$.
This is because the $S$ strain bacteria have a mucous (polysaccharide) coat,while the $R$ strain does not.
Mice infected with the $S$ strain (virulent) die from pneumonia infection,but mice infected with the $R$ strain do not develop pneumonia.
$S$ strain $\rightarrow$ Inject into mice $\rightarrow$ mice die
$R$ strain $\rightarrow$ Inject into mice $\rightarrow$ mice live
Griffith was able to kill bacteria by heating them.
He observed that heat-killed $S$ strain bacteria injected into mice did not kill them.
$S$ strain (heat-killed) $\rightarrow$ Inject into mice $\rightarrow$ mice live
$S$ strain (heat-killed) $+$ $R$ strain (live) $\rightarrow$ Inject into mice $\rightarrow$ mice die
When he injected a mixture of heat-killed $S$ and live $R$ bacteria,the mice died. Moreover,he recovered living $S$ bacteria from the dead mice.
He concluded that the $R$ strain bacteria had somehow been transformed by the heat-killed $S$ strain bacteria. Some 'transforming principle' transferred from the heat-killed $S$ strain had enabled the $R$ strain to synthesize a smooth polysaccharide coat and become virulent. This must be due to the transfer of the genetic material. However,the biochemical nature of the genetic material was not defined from his experiments.

(N/A) Prior to the work of Oswald Avery,Colin MacLeod,and Maclyn McCarty ($1933$-$1944$),the genetic material was thought to be a protein.
They worked to determine the biochemical nature of the 'transforming principle' in Griffith's experiment.
They purified biochemicals (proteins,$DNA$,$RNA$,etc.) from the heat-killed $S$ cells to see which ones could transform live $R$ cells into $S$ cells.
They discovered that $DNA$ alone from $S$ bacteria caused $R$ bacteria to become transformed.
They also discovered that protein-digesting enzymes (proteases) and $RNA$-digesting enzymes $(RNases)$ did not affect transformation,so the transforming substance was not a protein or $RNA$.
Digestion with $DNase$ did inhibit transformation,suggesting that the $DNA$ caused the transformation.
They concluded that $DNA$ is the hereditary material,but not all biologists were convinced.

(N/A) The unequivocal proof that $DNA$ is the genetic material came from the experiments of Alfred Hershey and Martha Chase $(1952)$.
They worked with viruses that infect bacteria,called bacteriophages.
$\Rightarrow$ The bacteriophage attaches to the bacteria,and its genetic material enters the bacterial cell.
The bacterial cell treats the viral genetic material as its own and subsequently manufactures more virus particles.
Hershey and Chase worked to discover whether it was protein or $DNA$ from the viruses that entered the bacteria.
They grew some viruses on a medium that contained radioactive phosphorus $(^{32}P)$ and others on a medium that contained radioactive sulfur $(^{35}S)$.
Viruses grown in the presence of radioactive phosphorus contained radioactive $DNA$ but not radioactive protein,because $DNA$ contains phosphorus while proteins do not.
Similarly,viruses grown on radioactive sulfur contained radioactive protein but not radioactive $DNA$,because $DNA$ does not contain sulfur.
Radioactive phages were allowed to attach to $E. coli$ bacteria.
Then,as the infection proceeded,the viral coats were removed from the bacteria by agitating them in a blender.
The virus particles were separated from the bacteria by spinning them in a centrifuge.
Bacteria infected with viruses that had radioactive $DNA$ were found to be radioactive,indicating that $DNA$ was the material that passed from the virus to the bacteria.
Bacteria infected with viruses that had radioactive proteins were not radioactive. This indicates that proteins did not enter the bacteria from the viruses.

(N/A) The $2'-OH$ group present at every nucleotide in $RNA$ makes it chemically reactive and structurally unstable. This makes $RNA$ prone to degradation and catalytic activity. In contrast,$DNA$ lacks this $2'-OH$ group,making it chemically less reactive and structurally more stable. Furthermore,the presence of thymine instead of uracil in $DNA$ provides additional stability. Due to these factors,$DNA$ is better suited for the storage of genetic information,making it the preferred genetic material in the majority of organisms.

(C) In $1869$,the Swiss chemist $Friedrich$ $Miescher$ first identified $DNA$ in the nuclei of human white blood cells. He called this substance 'nuclein'. Later,it was renamed as $DNA$ (Deoxyribonucleic acid).

(B) In $1869$,Friedrich Miescher identified a substance from the nuclei of pus cells (leukocytes) and named it 'Nuclein'.
Later,due to its acidic nature,it was renamed as nucleic acid,which we now know as $DNA$.

(D) In all living organisms,including eukaryotes and prokaryotes,$DNA$ serves as the genetic material.
However,in the case of viruses,the genetic material can be either $DNA$ or $RNA$.
For example,bacteriophages like $\phi \times 174$ contain $DNA$,while viruses like Tobacco Mosaic Virus $(TMV)$ and $Q\beta$ bacteriophage contain $RNA$ as their genetic material.
Therefore,$DNA$ is the genetic material in eukaryotes,prokaryotes,and some viruses.

(C) Frederick Griffith conducted a series of experiments in $1928$ using the bacterium $Streptococcus$ $pneumoniae$ (also known as $Diplococcus$ $pneumoniae$).
He observed the phenomenon of bacterial transformation,where a non-virulent strain of bacteria was transformed into a virulent strain by a 'transforming principle' derived from heat-killed virulent bacteria.
This experiment provided the first evidence that $DNA$ could be the genetic material.

(A) Frederick Griffith conducted his famous transformation experiments using the bacterium $Streptococcus \text{ } pneumoniae$ in the year $1928$.
In these experiments, he observed that a non-virulent strain of bacteria could be transformed into a virulent strain by a 'transforming principle' derived from heat-killed virulent bacteria.

(B) In $1928$,Frederick Griffith performed a series of experiments with $Streptococcus$ $pneumoniae$ (the bacterium responsible for pneumonia).
He used two strains of this bacterium:
$1$. $S$-strain (Smooth): These bacteria have a polysaccharide coat (mucous) and are virulent (cause disease).
$2$. $R$-strain (Rough): These bacteria lack the polysaccharide coat and are non-virulent (do not cause disease).
Therefore,a total of $2$ strains were used in his experiment.

(A) In the experiment conducted by Frederick Griffith on Streptococcus pneumoniae,two strains were identified:
$1$. The $S$ strain (Smooth),which possesses a mucous polysaccharide coat. This coat makes the bacteria virulent and capable of causing pneumonia in mice.
$2$. The $R$ strain (Rough),which lacks this mucous coat and is non-virulent.
Therefore,the correct answer is the $S$ strain.

(B) In Frederick Griffith's transformation experiment,he used two strains of Streptococcus pneumoniae:
$1$. The $S$ strain (Smooth),which has a polysaccharide coat and is virulent,forming smooth colonies.
$2$. The $R$ strain (Rough),which lacks the polysaccharide coat and is non-virulent,forming rough colonies.
Therefore,the $R$ strain is responsible for forming rough colonies.

(D) In the experiment conducted by $Frederick \ Griffith$ on $Streptococcus \ pneumoniae$,he identified two strains: $S$-strain (smooth) and $R$-strain (rough).
The $S$-strain bacteria are virulent because they possess a mucous coat or capsule made of polysaccharides.
This polysaccharide capsule protects the bacteria from the host's immune system,allowing them to cause disease (pneumonia).
The $R$-strain lacks this capsule and is therefore non-virulent.