RNA World Questions in English

(D) $RNA$ stands for Ribonucleic Acid. It is a polymer of nucleotides. Each nucleotide in $RNA$ consists of a nitrogenous base,a phosphate group,and a pentose sugar. The specific pentose sugar present in $RNA$ is Ribose sugar,which distinguishes it from $DNA$ (which contains Deoxyribose sugar).

(A) $mRNA$ (messenger $RNA$) is the shortest-lived $RNA$ molecule in the cell. It is synthesized to carry genetic information from the $DNA$ to the ribosomes for protein synthesis. Once the translation process is complete,$mRNA$ is rapidly degraded by cellular enzymes,making its lifespan significantly shorter compared to $tRNA$ and $rRNA$,which are more stable and involved in multiple rounds of protein synthesis.

(C) $rRNA$ (ribosomal $RNA$) is the most abundant type of $RNA$ in a cell,accounting for approximately $70-80\%$ of the total cellular $RNA$. It exists in $3-4$ different types and plays a crucial role in the structure and function of ribosomes during protein synthesis.

(C) There are three main types of ribonucleic acids $(RNA)$ found in cells:
$(1)$ Messenger $RNA$ $(mRNA)$ - It carries the genetic code from $DNA$ to the ribosome.
$(2)$ Transfer $RNA$ $(tRNA)$ - It brings specific amino acids to the ribosome during protein synthesis.
$(3)$ Ribosomal $RNA$ $(rRNA)$ - It forms the structural and catalytic components of the ribosome.
Therefore,the correct answer is $3$ types.

(D) In the year $2002$,the scientific journal 'Science' declared the discovery of $miRNA$ (microRNA) as the 'Breakthrough of the Year'. $miRNA$ are small non-coding $RNA$ molecules,typically about $21-23$ nucleotides in length,that play a crucial role in gene regulation by silencing target genes.

(C) $mRNA$ (messenger $RNA$) carries genetic information from the $DNA$ in the nucleus to the ribosomes in the cytoplasm for the synthesis of proteins.
It was named messenger $RNA$ by $Jacob$ and $Monod$ in $1961$.
It constitutes approximately $5\%$ of the total cellular $RNA$.

(C) In eukaryotic cells,the stability of $mRNA$ varies significantly. While some $mRNA$ molecules are very short-lived,the average half-life of $mRNA$ in eukaryotes is typically observed to be around $30$ minutes. This allows for dynamic regulation of gene expression in response to cellular needs.

(C) $tRNA$ contains a high proportion of modified nitrogenous bases compared to other types of $RNA$.
These modifications include pseudouridine $(\Psi)$, dihydrouridine $(DHU)$, and inosine $(I)$.
These chemical modifications are essential for the structural stability and functional folding of the $tRNA$ molecule into its characteristic clover-leaf or $L$-shaped tertiary structure.

(C) The catalytic property of $RNA$ was discovered by Thomas Cech and Sidney Altman. They demonstrated that $RNA$ molecules can act as biological catalysts,which are known as $Ribozymes$. Therefore,the correct option is $C$.

(C) Ribozyme is an $RNA$ molecule that possesses catalytic activity. Unlike most enzymes which are proteins,Ribozymes are composed of ribonucleic acid. $A$ well-known example is the $23S$ $rRNA$ in bacteria,which acts as a ribozyme for peptide bond formation during translation.

(B) In $DNA$,the base pairing follows Chargaff's rule,where the ratio of $A+T/G+C$ is constant for a given species. However,$RNA$ is typically single-stranded and does not follow Chargaff's base-pairing rules. Therefore,the ratios of $A/U$ and $G/C$ are not constant and vary significantly depending on the specific $RNA$ molecule and the species from which it is derived.

(B) Non-genetic $RNA$ is classified into three main types: $mRNA$ (messenger $RNA$),$tRNA$ (transfer $RNA$),and $rRNA$ (ribosomal $RNA$).
These three types of $RNA$ are directly involved in the process of protein synthesis in the cell.

(C) $mRNA$ (messenger $RNA$) is a non-genetic $RNA$ molecule that carries the genetic code from $DNA$ to the ribosomes. It contains the instructions for the sequence of specific amino acids that need to be linked together to form a polypeptide chain,making it essential for protein synthesis.

(A) ribozyme is an $RNA$ molecule that possesses catalytic activity.
In certain biological reactions,$RNA$ molecules can fold into specific three-dimensional structures and catalyze biochemical reactions,similar to protein-based enzymes.
This discovery challenged the traditional view that only proteins could function as biological catalysts.
Therefore,the correct statement is that $RNA$ acts as an enzyme.

(B) In nucleic acids,the nitrogenous bases are categorized into purines and pyrimidines.
$DNA$ contains the pyrimidines Cytosine and Thymine,while $R.N.A$ contains Cytosine and Uracil.
Thymine is specific to $DNA$,whereas Uracil is specific to $R.N.A$.
Therefore,Uracil is the base present only in $R.N.A$.

(C) In $DNA$,the four nitrogenous bases are $Adenine$ $(A)$,$Guanine$ $(G)$,$Cytosine$ $(C)$,and $Thymine$ $(T)$.
In $RNA$,$Thymine$ is replaced by $Uracil$ $(U)$.
Therefore,$RNA$ contains $Adenine$,$Guanine$,$Cytosine$,and $Uracil$.

(A) In a typical cell,there are three main types of $RNA$: $r-RNA$ (ribosomal $RNA$),$t-RNA$ (transfer $RNA$),and $m-RNA$ (messenger $RNA$).
$r-RNA$ constitutes about $80\%$ of the total cellular $RNA$ content.
$t-RNA$ accounts for approximately $15\%$ of the total $RNA$.
$m-RNA$ makes up only about $1-5\%$ of the total $RNA$.
Therefore,$r-RNA$ is the most abundant $RNA$ in the cell.

(B) $RNA$ is typically a single-stranded molecule. Unlike $DNA$,which follows Chargaff's rule ($A=T$ and $G=C$ due to double-stranded base pairing),$RNA$ does not have a fixed base-pairing requirement for its entire length. Therefore,the concentration of Adenine $(A)$ does not necessarily equal Uracil $(U)$,and Guanine $(G)$ does not necessarily equal Cytosine $(C)$. Thus,$A \neq U$ and $G \neq C$ is the correct statement for $RNA$.

(B) $RNA$ stands for Ribonucleic Acid.
It is a polymer of nucleotides.
Each nucleotide in $RNA$ consists of a nitrogenous base,a phosphate group,and a pentose sugar.
The specific pentose sugar present in $RNA$ is Ribose sugar.
Therefore,the backbone of $RNA$ is composed of alternating Ribose sugar and phosphate groups.

(C) In a typical cell,$r-RNA$ (ribosomal $RNA$) is the most abundant type of $RNA$,accounting for approximately $80\%$ of the total cellular $RNA$.
$t-RNA$ (transfer $RNA$) accounts for about $15\%$ of the total $RNA$.
$m-RNA$ (messenger $RNA$) is the least abundant,accounting for only about $1-5\%$ of the total $RNA$ content in the cell.

(C) The $t-RNA$ (transfer $RNA$) is the smallest type of $RNA$ molecule.
It typically consists of $73$ to $93$ nucleotides.
In contrast,$r-RNA$ molecules are much larger as they form the structural components of ribosomes,and $m-RNA$ molecules vary significantly in length depending on the size of the protein they encode.

(A) The correct answer is $A$. Chromosomes are primarily composed of $DNA$ and proteins (histones). While $RNA$ is synthesized in the nucleus (transcription) and found in the cytoplasm and ribosomes,it is not a structural component of the chromosome itself. $DNA$ is the genetic material in chromosomes.

(D) The $t-RNA$ (transfer $RNA$) molecule is known to have a cloverleaf-like secondary structure.
This structure consists of several loops, including the anticodon loop, the $D-loop$, and the $T\psi C$ loop, which are essential for its function in protein synthesis.
In its three-dimensional form, $t-RNA$ appears as an inverted $L$-shaped molecule.

(D) Severo Ochoa was awarded the Nobel Prize in Physiology or Medicine in $1959$ for his discovery of the mechanisms in the biological synthesis of ribonucleic acid $(RNA)$ and deoxyribonucleic acid $(DNA)$. Specifically,he discovered the enzyme polynucleotide phosphorylase,which allowed for the in vitro synthesis of polyribonucleotides.

(C) Ribonucleic acid $(RNA)$ is a versatile molecule found in various parts of the cell.
$1$. In the nucleus,$RNA$ is synthesized during the process of transcription from $DNA$.
$2$. In the cytoplasm,$RNA$ (specifically $mRNA$,$tRNA$,and $rRNA$) is present to facilitate the process of protein synthesis (translation).
$3$. Therefore,$RNA$ is present in both the nucleus and the cytoplasm of a eukaryotic cell.

(C) The term '$RNA$ world' was proposed because it was discovered that $RNA$ molecules can act as catalysts,known as ribozymes.
This discovery challenged the idea that only proteins (enzymes) could catalyze biochemical reactions.
Since $RNA$ can both store genetic information and catalyze reactions,it is hypothesized that $RNA$ was the first self-replicating molecule in the early stages of evolution.

(B) Transfer $RNA$ $(tRNA)$ molecules are relatively small,single-stranded molecules that function as adapters during protein synthesis.
Most $tRNA$ molecules consist of a chain of approximately $73$ to $93$ nucleotides.
Among the given options,$75$ is the most representative value for the average length of a $tRNA$ molecule.
Therefore,the correct option is $B$.

(A) $RNA$ stands for Ribonucleic Acid. It is a polymer of ribonucleotides. Unlike $DNA$,which is typically double-stranded,$RNA$ is generally a single-stranded molecule. It consists of a single polynucleotide chain that can fold upon itself to form complex secondary structures.

(D) In biological systems,there are three main types of $RNA$ involved in protein synthesis: $mRNA$ (Messenger-$RNA$),$tRNA$ (Transfer-$RNA$),and $rRNA$ (Ribosomal-$RNA$).
Ribozyme is not a type of $RNA$ molecule itself; rather,it refers to an $RNA$ molecule that possesses catalytic activity (acting as an enzyme).
Therefore,Ribozyme is not classified as a structural or functional type of $RNA$ in the context of the genetic code and protein synthesis machinery.

(A) $RNA$ stands for Ribonucleic Acid.
It is a polymer of ribonucleotides.
Unlike $DNA$,which is typically double-stranded,$RNA$ is generally a single-stranded molecule.
Therefore,the structure of $RNA$ consists of a single polynucleotide chain.

(A) $RNA$ stands for Ribonucleic acid. It is a polymeric molecule essential in various biological roles in coding,decoding,regulation,and expression of genes. It is one of the two main types of nucleic acids,the other being $DNA$ (Deoxyribonucleic acid).

(C) In biological systems,there are three main types of $RNA$ that are required for the process of protein synthesis:
$1$. $mRNA$ (messenger $RNA$): It acts as a template for protein synthesis.
$2$. $tRNA$ (transfer $RNA$): It brings amino acids and reads the genetic code.
$3$. $rRNA$ (ribosomal $RNA$): It plays a structural and catalytic role during translation.
Therefore,the correct answer is $3$.

(B) In biological systems,there are three main types of $RNA$ involved in the process of protein synthesis:
$1$. Messenger $RNA$ $(mRNA)$: It carries the genetic information from $DNA$ to the ribosome.
$2$. Transfer $RNA$ $(tRNA)$: It brings specific amino acids to the ribosome during translation.
$3$. Ribosomal $RNA$ $(rRNA)$: It forms the structural and catalytic components of the ribosome.
Among the given options,$t-RNA$ is a recognized type of $RNA$.

(D) In living organisms,there are three main types of $RNA$ that are required for the synthesis of proteins:
$1$. $m-RNA$ (Messenger $RNA$): It carries the genetic information from $DNA$ to the ribosome.
$2$. $t-RNA$ (Transfer $RNA$): It brings specific amino acids to the ribosome during translation.
$3$. $r-RNA$ (Ribosomal $RNA$): It forms the structural and catalytic components of the ribosome.
Therefore,all three types are essential components of the protein synthesis machinery.

(D) In a typical cell,the distribution of different types of $RNA$ is as follows:
$1$. $r-RNA$ (Ribosomal $RNA$) constitutes the majority of the total cellular $RNA$,accounting for approximately $80\%$ to $85\%$ of the total.
$2$. $t-RNA$ (Transfer $RNA$) accounts for about $15\%$ of the total $RNA$.
$3$. $m-RNA$ (Messenger $RNA$) accounts for about $1\%$ to $5\%$ of the total $RNA$.
Therefore,the correct range for $r-RNA$ is $80\%$ to $85\%$.

(C) typical $t-RNA$ (transfer $RNA$) molecule is a small $RNA$ molecule,usually consisting of $73$ to $93$ nucleotides. Among the given options,$75$ is the most representative value for the length of a standard $t-RNA$ molecule.

(A) The secondary structure of $tRNA$ is depicted as a clover-leaf model. However,when viewed in its actual $3D$ configuration,the $tRNA$ molecule folds into a compact $L$-shaped structure. This $3D$ shape is essential for its function in protein synthesis,allowing it to interact with both the ribosome and the $mRNA$ template.

(C) The term '$RNA$ world' was proposed because research in the $1980s$ revealed that $RNA$ can act as a catalyst (ribozyme) in biochemical reactions.
This discovery suggested that $RNA$ could have been the first self-replicating molecule,capable of both storing genetic information and catalyzing chemical reactions,which predates the evolution of $DNA$ and proteins.

(C) Let us analyze the given statements:
$(i)$ $RNA$ can directly code for the synthesis of proteins: This is true, as $mRNA$ acts as a template for protein synthesis.
$(ii)$ It is a very common process to synthesize $DNA$ from $RNA$: This is false. The synthesis of $DNA$ from $RNA$ (reverse transcription) is not a common process in most organisms; it is primarily observed in retroviruses.
$(iii)$ $RNA$ is used as genetic material only in humans: This is false. $RNA$ serves as the genetic material in many viruses (e.g., $TMV$, $Q\beta$ bacteriophage), not just humans.
$(iv)$ One polynucleotide chain is present in $RNA$: This is true, as $RNA$ is typically single-stranded.
Therefore, statements $(ii)$ and $(iii)$ are false.

(A) The $RNA$ world hypothesis suggests that $RNA$ was the first genetic material and performed both catalytic and coding functions.
Splicing,the removal of introns from pre-$mRNA$,is a complex process that highlights the catalytic capabilities of $RNA$ (ribozymes),which is a hallmark of the $RNA$ world.
Introns are considered 'junk' or non-coding sequences in modern eukaryotes,but their presence is widely regarded as a remnant of the ancient $RNA$ world,suggesting that the split-gene arrangement is an ancestral feature.
Therefore,both the assertion $(A)$ and the reason $(R)$ are correct,and $R$ provides a valid context for the evolutionary significance of $RNA$ processing.

(C) $RNA$ (Ribonucleic acid) is typically a single-stranded molecule.
Option $C$ states that $RNA$ contains two polynucleotide chains,which is incorrect because $RNA$ is generally single-stranded,whereas $DNA$ is double-stranded.
$RNA$ plays a crucial role in protein synthesis $(Option A)$.
$tRNA$ acts as an adapter molecule that brings specific amino acids to the ribosome and reads the genetic code via its anticodon $(Option B)$.
$rRNA$ (ribosomal $RNA$) acts as a structural component and also functions as a ribozyme (catalyst) during the formation of peptide bonds in translation $(Option D)$.

(B) $RNA$ stands for Ribonucleic Acid.
It is a polymer of nucleotides.
Each nucleotide consists of a nitrogenous base, a phosphate group, and a pentose sugar.
The pentose sugar present in $RNA$ is Ribose sugar, which has a hydroxyl $(-OH)$ group at the $2'$ carbon position.
In contrast, $DNA$ contains Deoxyribose sugar, which lacks the oxygen atom at the $2'$ position.

(C) The concept of the '$RNA$ World' was proposed because $RNA$ is capable of both storing genetic information and acting as a catalyst. In the $1980s$,it was discovered that certain $RNA$ molecules,known as ribozymes,possess enzymatic activity (e.g.,self-splicing introns and ribosomal $RNA$ acting as a peptidyl transferase). This dual functionality suggests that $RNA$ could have been the first self-replicating molecule in the early stages of evolution.

(A) In a typical animal cell,$r-RNA$ (ribosomal $RNA$) is the most abundant type of $RNA$,accounting for approximately $80\%$ of the total cellular $RNA$.
$t-RNA$ (transfer $RNA$) accounts for about $15\%$ of the total $RNA$.
$m-RNA$ (messenger $RNA$) is the least abundant,typically making up only $1-5\%$ of the total cellular $RNA$ because it is rapidly synthesized and degraded based on the cell's protein synthesis requirements.

(D) In $DNA$,the four nitrogenous bases are Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Thymine $(T)$.
In $RNA$,Thymine is replaced by Uracil $(U)$.
Therefore,the base pairing in $RNA$ involves Adenine,Guanine,Cytosine,and Uracil.

(D) The $t-RNA$ (transfer $RNA$) molecule is known to have a clover-leaf secondary structure.
In this structure, the molecule folds into loops, including the anticodon loop, the $D$-loop, and the $T\psi C$-loop.
This structure is essential for its function in protein synthesis, where it carries specific amino acids to the ribosome based on the codon sequence of $m-RNA$.

(B) . $G. Mendel$ is known for the laws of inheritance,not transformation. Transformation was discovered by $F. Griffith$.
$B$. Ribozyme is an $RNA$ molecule that acts as an enzyme,which is a nucleic acid. This is the correct match.
$C$. $T.H. Morgan$ is known for linkage and recombination,not transduction. Transduction was discovered by $Zinder$ and $Lederberg$.
$D$. $F_2 \times$ Recessive parent is a test cross,not a dihybrid cross. $A$ dihybrid cross involves the study of two traits.

(N/A) $RNA$ (Ribonucleic acid) is a polymer of nucleotides. Each nucleotide consists of a nitrogenous base,a pentose sugar (ribose),and a phosphate group.
The presence of a $2'-OH$ group on every ribose sugar in $RNA$ makes it a reactive group,which renders $RNA$ labile and easily degradable.
$RNA$ was the first genetic material. There is sufficient evidence to suggest that essential life processes,such as metabolism,translation,and splicing,evolved around $RNA$.
$RNA$ functioned as both a genetic material and a catalyst. Certain biochemical reactions in living systems are still catalyzed by $RNA$ (ribozymes) rather than protein enzymes.
Because $RNA$ was reactive and unstable as a catalyst,$DNA$ evolved from $RNA$ with chemical modifications (specifically the loss of the $2'-OH$ group) to become more stable.
$DNA$ is double-stranded and possesses a complementary strand,which allows for a repair mechanism,further ensuring its stability as the primary genetic material.

(N/A) $RNA$ was the first genetic material. Essential life processes like metabolism and translation evolved around $RNA$. $RNA$ acts as both a genetic material and a catalyst (ribozyme). However,$RNA$ is reactive and unstable as a catalyst.
Due to this,$DNA$ evolved from $RNA$ through chemical modifications,making it more stable. Furthermore,$DNA$ is resistant to mutations due to its double-stranded structure and the evolution of repair mechanisms.

(C) Both $DNA$ and $RNA$ are capable of mutation.
However,$RNA$ is inherently less stable than $DNA$ because it is a single-stranded molecule and lacks the proofreading mechanisms associated with $DNA$ replication.
Because $RNA$ is unstable,it mutates at a significantly faster rate.
Consequently,viruses with an $RNA$ genome,which often have shorter lifespans and faster replication cycles,evolve and mutate much more rapidly than $DNA$ viruses.