The Search for Genetic Material Questions in English

(C) Howard Temin and David Baltimore $(1975)$ independently discovered the process of reverse transcription. This process is characteristic of retroviruses,which use the enzyme reverse transcriptase to convert their $RNA$ genome into $DNA$ within the host cell.

(C) Bacteriophages are viruses that infect bacteria. During the final stage of the lytic cycle,the phage needs to release its progeny from the host cell. To achieve this,the phage produces specific enzymes that degrade the bacterial cell wall,which is primarily composed of peptidoglycan. These enzymes are collectively known as endolysins (or phage-lysozymes). Endolysins are muralytic enzymes that target the bonds in the peptidoglycan layer,causing the bacterial cell wall to rupture (lysis) and allowing the release of new viral particles.

(D) Alfred Hershey and Martha Chase conducted experiments in $1952$ to determine whether $DNA$ or protein was the genetic material.
They used the $T_2$ bacteriophage,a virus that infects bacteria $(E. coli)$.
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 bacteriophages to infect the bacteria,they found that only radioactive phosphorus $(^{32}P)$ was transferred into the bacterial cells,proving that $DNA$ is the genetic material.

(A) Frederick Griffith's transformation experiments conducted in $1928$ using $Streptococcus$ $pneumoniae$ (also known as $Pneumococcus$) demonstrated that a 'transforming principle' from heat-killed virulent bacteria could transform non-virulent bacteria into virulent ones.
Later,Avery,MacLeod,and McCarty built upon this work to identify that this transforming principle was $DNA$,thereby leading to the hypothesis that $DNA$ is the genetic material.

(B) Sulphur is a key component of specific amino acids such as cysteine,cystine,and methionine.
Since these amino acids are the building blocks of proteins,bacteria grown in a medium containing radioactive $S^{35}$ will incorporate this isotope into their proteins.

(B) The proof that $DNA$ is the genetic material was first provided by Frederick Griffith in $1928$ through his experiments on $Streptococcus$ $pneumoniae$. This process is known as bacterial transformation,where a non-virulent strain of bacteria takes up genetic material from a heat-killed virulent strain,thereby acquiring its characteristics. Later,Avery,MacLeod,and McCarty confirmed that the transforming principle was indeed $DNA$.

(B) The phenomenon of bacterial transformation was first discovered by Frederick Griffith in $1928$ while working with $Diplococcus$ $pneumoniae$.
He observed that a non-virulent strain of bacteria could be transformed into a virulent strain by a 'transforming principle' from heat-killed virulent bacteria.
Later,in $1944$,Oswald Avery,Colin MacLeod,and Maclyn McCarty identified this 'transforming principle' as $DNA$,providing the biochemical evidence for transformation.

(D) The transformation experiment was conducted by Frederick Griffith in $1928$. He used the bacterium $Diplococcus$ $pneumoniae$ (also known as $Streptococcus$ $pneumoniae$) to demonstrate the phenomenon of bacterial transformation. In this experiment,he observed that a non-virulent strain of bacteria could be transformed into a virulent strain by taking up genetic material from heat-killed virulent bacteria.

(B) The protein coat of a bacteriophage contains sulfur-containing amino acids (like methionine and cysteine) but lacks phosphorus.
Conversely,nucleic acids $(DNA)$ contain phosphorus but lack sulfur.
To label the protein coat specifically without labeling the nucleic acid,the bacteriophage must be grown in a medium containing radioactive sulfur $(S^{35})$.
Therefore,the correct option is $B$.

(D) The unequivocal proof that $DNA$ is the genetic material came from the experiments of Alfred Hershey and Martha Chase in $1952$.
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.
Radioactive phages were allowed to infect $E. coli$ bacteria.
After infection,the viral coats were removed from the bacteria by agitating them in a blender.
Then,the virus particles were separated from the bacteria by spinning them in a centrifuge.
Bacteria which 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.
This proved that $DNA$ is the genetic material that is passed from virus to bacteria.

(C) The transformation experiments conducted by Frederick Griffith on $Streptococcus$ $pneumoniae$ (Pneumococcus) were further refined by Avery, MacLeod, and McCarty.
They purified biochemicals (proteins, $DNA$, and $RNA$) from the heat-killed $S$ strain to see which one could transform live $R$ strain bacteria into $S$ strain.
They discovered that digestion of protein and $RNA$ with enzymes did not affect transformation, but digestion with $DNase$ inhibited the transformation process.
This conclusively proved that $DNA$ is the hereditary material responsible for transformation.

(C) $DNA$ was first identified by Friedrich Miescher in $1869$. He isolated it from the nuclei of pus cells and called it 'nuclein'.

(B) The strongest evidence for $DNA$ as the genetic material comes from the transformation experiments conducted by Frederick Griffith and later confirmed by Avery,MacLeod,and McCarty.
In these experiments,the transformation of non-virulent $R$-strain bacteria into virulent $S$-strain bacteria occurred due to the transfer of $DNA$ from heat-killed $S$-strain bacteria.
This demonstrated that $DNA$ is the molecule responsible for carrying genetic information and causing the transformation of bacterial cells.

(A) The Nobel Prize in Physiology or Medicine in $1959$ was awarded jointly to Severo Ochoa and Arthur Kornberg.
Severo Ochoa received the prize for his discovery of the mechanisms in the biological synthesis of $RNA$ (ribonucleic acid) using the enzyme polynucleotide phosphorylase.
Arthur Kornberg received the prize for his discovery of the mechanisms in the biological synthesis of $DNA$ (deoxyribonucleic acid).
Therefore,the correct answer is $S. Ochoa$.

(A) . Frederick Griffith discovered the phenomenon of bacterial transformation in $1928$ using $Streptococcus$ $pneumoniae$.
$B$. Friedrich Miescher isolated $DNA$ for the first time from pus cells,calling it 'nuclein'.
$C$. The one gene one polypeptide hypothesis was proposed by Beadle and Tatum.
$D$. The concept of inborn errors of metabolism was proposed by Archibald Garrod.

(B) The Feulgen stain is a staining technique discovered by Robert Feulgen and $H$. Rossenbeck in $1924$. It is a cytochemical method used to identify chromosomal material or $DNA$ in cell specimens. The method relies on the acid hydrolysis of $DNA$,which exposes aldehyde groups that then react with the Schiff reagent to produce a distinct magenta color,allowing for the visualization of $DNA$ within the nucleus.

(B) The correct answer is $B$. Oswald Avery,Colin MacLeod,and Maclyn McCarty $(1944)$ conducted experiments to determine the biochemical nature of the 'transforming principle' observed by Frederick Griffith. They purified biochemicals (proteins,$DNA$,$RNA$,etc.) from heat-killed $S$ cells and discovered that only $DNA$ from heat-killed $S$ cells could transform live $R$ cells into $S$ cells. They also discovered that protein-digesting enzymes (proteases) and $RNA$-digesting enzymes $(RNases)$ did not affect transformation,whereas $DNA$-digesting enzymes $(DNases)$ inhibited it. Thus,they concluded that $DNA$ is the hereditary material.

(C) In $1928$,Frederick Griffith performed a series of experiments with $Streptococcus$ $pneumoniae$ (formerly known as $Diplococcus$ $pneumoniae$).
He used two strains of this bacterium: $S$-strain (virulent,smooth,encapsulated) and $R$-strain (non-virulent,rough,non-encapsulated).
This experiment provided the first evidence of the 'transforming principle',which later led to the discovery of $DNA$ as the genetic material.

(B) The process of reverse transcription was discovered by Howard Temin and David Baltimore in the $1970s$. It was first observed in the Rous sarcoma virus $(RSV)$,which is an $RNA$ virus. These viruses possess an enzyme called reverse transcriptase,which allows them to synthesize $DNA$ from an $RNA$ template.

(A) The material that controls heredity and carries genetic information from one generation to the next is $DNA$ (Deoxyribonucleic acid).
Chromosomes are composed of $DNA$ and proteins (primarily histones).
While histones provide structural support for packaging $DNA$,the actual genetic instructions are encoded within the $DNA$ molecule itself.

(B) George Beadle and Edward Tatum developed the method of identifying nutritional mutants in the bread mold $Neurospora$ $crassa$.
They used $X$-rays to induce mutations in the fungus and then screened for strains that could not synthesize specific nutrients,leading to the formulation of the 'one gene-one enzyme' hypothesis.

(B) The replica plating experiment was performed by Joshua Lederberg and Esther Lederberg in $1952$.
This experiment provided direct evidence for the existence of pre-existing mutations in bacterial populations.
It demonstrated that mutations occur randomly and are not induced by the environment,supporting the Darwinian view of natural selection.

(B) In the infection process of a bacteriophage,the virus attaches to the surface of the host bacterium.
It injects its genetic material (usually $DNA$) into the host cell,while the protein coat (capsid) remains outside.
Once inside,the viral $DNA$ takes over the host's machinery to replicate itself and produce new viral proteins,leading to the assembly of new bacteriophages.

(B) Transduction is a mechanism of horizontal gene transfer in bacteria where $DNA$ is transferred from one bacterium to another by a virus (bacteriophage).
During the lytic cycle,the phage may accidentally package bacterial $DNA$ instead of viral $DNA$.
When this phage infects a new recipient cell,it injects the donor bacterial $DNA$ into the recipient,which can then be integrated into the recipient's genome.

(A) Transduction is a process of horizontal gene transfer where bacterial $DNA$ is transferred from one bacterium to another by a virus (bacteriophage).
This phenomenon was first discovered by Norton Zinder and Joshua Lederberg in $1952$.
They observed this process while studying the bacterium $Salmonella \ typhimurium$.

(A) The transformation experiments conducted by Frederick Griffith in $1928$ using $Streptococcus$ $pneumoniae$ (also known as $Pneumococcus$) demonstrated that a 'transforming principle' could transfer genetic information from heat-killed virulent bacteria to live non-virulent bacteria,causing them to become virulent. Later,Avery,MacLeod,and McCarty biochemically characterized this principle and concluded that $DNA$ is the hereditary material.

(B) The phylogenetic history of organisms is primarily determined by analyzing the sequence of $r-RNA$ (ribosomal $RNA$),specifically the $16S$ $r-RNA$ in prokaryotes and $18S$ $r-RNA$ in eukaryotes.
$r-RNA$ genes are highly conserved across different species because they are essential for protein synthesis.
Due to their slow mutation rate,they serve as an excellent 'molecular chronometer' to trace evolutionary relationships and construct phylogenetic trees.

(A) The unequivocal proof that $DNA$ is the genetic material came from the experiments conducted by Alfred Hershey and Martha Chase in $1952$.
They worked with bacteriophages,which are viruses that infect bacteria.
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.
After allowing the phages to infect $E. coli$ bacteria,they observed that only radioactive phosphorus $(^{32}P)$ was found inside the bacterial cells,indicating that $DNA$ had entered the cell.
This confirmed that $DNA$ is the genetic material,not protein.

(A) The unequivocal proof that $DNA$ is the genetic material came from the experiments of Alfred Hershey and Martha Chase in $1952$. They worked with bacteriophages,which are viruses that infect bacteria. By using radioactive isotopes ($^{32}P$ to label $DNA$ and $^{35}S$ to label proteins),they demonstrated that only $DNA$ entered the bacterial cell,while the protein coat remained outside. This confirmed that $DNA$ is the genetic material that carries hereditary information.

(A) Alfred Hershey and Martha Chase $(1952)$ conducted experiments using bacteriophages,which are viruses that infect 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.
These viruses were allowed to infect $Escherichia$ $coli$ bacteria.
After infection,the viral coats were removed from the bacteria by agitation in a blender and centrifugation.
They observed that radioactive phosphorus $(^{32}P)$ was found inside the bacterial cells,indicating that $DNA$ had entered the bacteria.
Conversely,radioactive sulfur $(^{35}S)$ was found only in the supernatant,indicating that proteins did not enter the bacteria.
Thus,they provided unequivocal proof that $DNA$ is the genetic material.

(A) The unequivocal proof that $DNA$ is the genetic material came from the experiments conducted by Alfred Hershey and Martha Chase in $1952$.
They worked with bacteriophages,which are viruses that infect bacteria.
They grew some bacteriophages in a medium containing radioactive phosphorus $(^{32}P)$ to label the $DNA$,and others in a medium containing radioactive sulfur $(^{35}S)$ to label the proteins.
When these labeled phages infected $E. coli$ bacteria,it was observed that only the radioactive phosphorus $(^{32}P)$ entered the bacterial cells,indicating that $DNA$,not protein,is the genetic material that enters the host to direct the production of new viral particles.

(C) Reverse transcription is the process of synthesizing $DNA$ from an $RNA$ template,which is catalyzed by the enzyme reverse transcriptase.
This phenomenon was independently discovered by Howard Temin and David Baltimore in $1970$ while studying $RNA$ tumor viruses.
Therefore,the correct answer is Temin and Baltimore.

(B) Barbara McClintock was awarded the Nobel Prize in Physiology or Medicine in $1983$ for her discovery of mobile genetic elements, commonly known as 'jumping genes' or transposons, in maize $(Zea \, mays)$.
Her work demonstrated that these genetic elements could move within the genome, which challenged the then-prevailing view of a static genome.

(C) The "Replica Plating Experiment" was performed by $Joshua$ and $Esther$ $Lederberg$ in $1952$.
This experiment provided direct evidence for the pre-existence of bacterial mutants and demonstrated that mutations occur randomly rather than being induced by the environment.
By using a velvet pad to transfer bacterial colonies from a master plate to replica plates containing antibiotics, they showed that the antibiotic-resistant colonies were already present in the original population.

(D) George Beadle and Edward Tatum proposed the 'one gene one enzyme' hypothesis in $1941$.
They used the bread mold $Neurospora \, crassa$ as their model organism.
By inducing mutations in the mold using $X$-rays, they were able to create nutritional mutants (auxotrophs) that could not synthesize specific amino acids or vitamins, thereby demonstrating that specific genes control the production of specific enzymes.

(A) Heredity is the process by which genetic information is passed from parents to offspring. The molecule responsible for storing and transmitting this genetic information is the genetic material,which is $DNA$ (Deoxyribonucleic acid) in most organisms. Therefore,the genetic material is the component responsible for heredity.

(B) In $1869$,Friedrich Miescher first identified a substance he called 'nuclein' from the nuclei of pus cells. He was the first to isolate and characterize this material,which was later identified as $DNA$ (nucleic acid) associated with proteins.

(B) In $1869$,$Friedrich$ $Miescher$ identified a substance in the nuclei of pus cells (human white blood cells) that was weakly acidic and rich in phosphorus.
He named this substance '$Nuclein$'.
Later,due to its acidic nature,it was renamed '$Nucleic$ $acid$' by $Altmann$.

(B) In $1869$,Friedrich Miescher identified a substance he called 'nuclein' from the nuclei of pus cells. He was the first to isolate and characterize this material,which was later identified as nucleic acid $(DNA)$ associated with proteins.

(D) $DNA$ was first identified by Friedrich Miescher in $1869$. He isolated a substance from the nuclei of pus cells (which are primarily white blood cells or leukocytes) obtained from discarded surgical bandages. He named this substance 'nuclein'. Later,it was found to be weakly acidic and was renamed 'nucleic acid' (now known as $DNA$). Among the given options,leukocytes (white blood cells) are the correct source.

(D) In $1869$,Friedrich Miescher identified a substance in the nuclei of pus cells,which he named 'Nuclein'.
Later,due to its acidic nature,it was renamed 'Nucleic acid' by Richard Altmann.
Therefore,the correct term originally used by Miescher is 'Nuclein'.

(C) In $1869$,the Swiss biochemist $Friedrich$ $Miescher$ identified a substance in the nuclei of pus cells (white blood cells) which he named 'Nuclein'.
Later,this substance was identified as $DNA$ (deoxyribonucleic acid).
Therefore,the term 'Nuclein' is associated with $Friedrich$ $Miescher$.

(C) In $1920$,researchers identified that nucleic acids are a major component of chromosomes. This discovery was crucial in understanding that chromosomes,which carry genetic information,are composed of $DNA$ and proteins.

(C) In $1869$,Friedrich Miescher identified a substance in the nuclei of pus cells,which he named 'nuclein'.
Chemical analysis revealed that nuclein is rich in phosphorus and exhibits acidic properties.
Therefore,Miescher classified nuclein as a weak acid.

(C) The genetic material is the substance that carries biological information from one generation to the next. In almost all living organisms,$DNA$ (Deoxyribonucleic acid) serves as the primary genetic material. While some viruses use $RNA$ as their genetic material,$DNA$ is the universal genetic material for cellular life forms due to its chemical stability and ability to store complex information.

(A) The final proof that $DNA$ is the genetic material was provided by Alfred Hershey and Martha Chase in $1952$.
They worked with bacteriophages,which are viruses that infect bacteria.
They grew some bacteriophages in a medium containing radioactive phosphorus $(^{32}P)$ to label the $DNA$ and others in a medium containing radioactive sulfur $(^{35}S)$ to label the protein coat.
After allowing the phages to infect $E. coli$ bacteria,they agitated the mixture in a blender to remove the viral coats from the bacterial cells.
They found that radioactive phosphorus $(^{32}P)$ was present inside the bacterial cells,indicating that $DNA$ had entered the cells,while radioactive sulfur $(^{35}S)$ remained outside,indicating that proteins did not enter the cells.
This confirmed that $DNA$ is the genetic material.

(C) The correct answer is $C$. $A$ molecule that acts as genetic material must be stable both structurally and chemically. If the genetic material were unstable,it would lead to the loss of metabolic functions and genetic information over time. Therefore,the requirement that it should be 'unstable' is incorrect.

(C) Transformation was first studied by $F. Griffith$ in $1928$ while studying $Streptococcus$ $pneumoniae$.
He found that $R$-type non-virulent bacteria pick up virulence from heat-killed virulent $S$-type bacteria and transform into virulent forms.
It was this experiment which indicated the presence of a 'transforming principle', which was later identified as $DNA$ by $Avery$ et al.

(D) 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,which are known as bacteriophages.