Nucleic Acids Questions in English

(A) Nitrogenous bases in nucleic acids are classified into two types: purines and pyrimidines.
$1$. Pyrimidines are heterocyclic compounds containing two nitrogen atoms in a six-membered ring. Examples include $Cytosine$,$Uracil$,and $Thymine$.
$2$. Purines are heterocyclic compounds consisting of a six-membered ring fused to a five-membered ring,containing four nitrogen atoms. Examples include $Adenine$ and $Guanine$.
Therefore,$Guanine$ is a purine derivative,not a pyrimidine derivative.

(D) Nitrogenous bases in nucleic acids are classified into two types: purines and pyrimidines.
Purines have a double-ring structure (a six-membered ring fused to a five-membered ring),while pyrimidines have a single-ring structure.
Among the given options,$Thymine$,$Uracil$,and $Cytosine$ are pyrimidines (single-ring).
$Guanine$ is a purine and possesses a double-ring structure.
Therefore,the correct option is $D$.

(C) In nucleosides,the nitrogen atom at position $1$ $(N-1)$ of the pyrimidine base is covalently bonded to the $C-1'$ carbon atom of the furanose sugar.

(A) To determine the number of $N$ atoms in each compound,we examine their chemical structures:
$1$. Guanine $(C_5H_5N_5O)$: It contains $5$ nitrogen atoms.
$2$. Thymine $(C_5H_6N_2O_2)$: It contains $2$ nitrogen atoms.
$3$. Cytosine $(C_4H_5N_3O)$: It contains $3$ nitrogen atoms.
$4$. Uracil $(C_4H_4N_2O_2)$: It contains $2$ nitrogen atoms.
Comparing these,Guanine has the highest number of nitrogen atoms $(5)$.
Therefore,the correct option is $A$.

(C) In a nucleoside,the nitrogenous base is linked to the $C1'$ position of the sugar (ribose or deoxyribose) via a $\beta$-glycosidic linkage.
For purine bases (like adenine or guanine),this linkage occurs at the $N9$ nitrogen atom.
For pyrimidine bases (like cytosine,thymine,or uracil),this linkage occurs at the $N1$ nitrogen atom.
As shown in the provided structure,the furanose ring is attached to the $N9$ position of the purine base.

(B) The correct abbreviation for deoxyriboadenosine monophosphate is $dAMP$.
$d$ stands for deoxyribose,$A$ stands for adenosine,$M$ stands for monophosphate,and $P$ stands for phosphate.

(D) Uracil is not present in $DNA$. It is present in $RNA$.
$DNA$ contains four bases,i.e.,adenine $(A)$,guanine $(G)$,cytosine $(C)$,and thymine $(T)$.
In $RNA$,thymine $(T)$ is replaced by uracil $(U)$.

(C) The sugar present in $DNA$ is $2$-deoxyribose.
In ribose sugar,all carbon atoms ($C_1$ to $C_5$) are attached to an $-OH$ group.
However,in $2$-deoxyribose,the $-OH$ group at the $C_2$ position is replaced by a hydrogen atom $(-H)$.
Therefore,the $C_2$ carbon atom does not contain an $-OH$ group.

(C) $D-2-\text{deoxyribose}$ sugar molecule is present in $DNA$.

(D) The correct answer is $D$. $RNA$ contains adenine,guanine,cytosine,and uracil,not thymine. Thymine is present in $DNA$.

(B) The nitrogenous bases present in $DNA$ are Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Thymine $(T)$.
Uracil $(U)$ is a nitrogenous base found in $RNA$ instead of Thymine.
Therefore,Uracil is not present in the $DNA$ structure.
Thus,the correct option is $B$.

(C) Statement $(i)$ is False because $\text{Pentose sugar} + \text{base} \rightarrow \text{Nucleoside}$.
Statement $(ii)$ is False because $\text{Nucleoside} + \text{phosphate} \rightarrow \text{Nucleotide}$.
Statement $(iii)$ is True as $DNA$ contains Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Thymine $(T)$.
Statement $(iv)$ is True as $RNA$ contains Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Uracil $(U)$.
Thus,the sequence is $FFTT$.

(B) $(i)$ Cytosine is a pyrimidine derivative,so it is $T$.
$(ii)$ $DNA$ contains $2$-deoxy-$\beta-D$-ribose,not $\beta-D$-ribose (which is in $RNA$),so it is $F$.
$(iii)$ $RNA$ carries the genetic message for protein synthesis,so it is $T$.
$(iv)$ $DNA$ is responsible for the transmission of hereditary information over generations,not just for one century,so it is $F$.
Thus,the sequence is $T, F, T, F$. The correct option is $B$.

(D) Nitrogenous bases are classified into two types: purines and pyrimidines.
Purines include $Adenine$ $(A)$ and $Guanine$ $(G)$.
Pyrimidines include $Cytosine$ $(C)$,$Thymine$ $(T)$,and $Uracil$ $(U)$.
Therefore,$Guanine$ is a purine base.
The correct option is $D$.

(A) Nitrogenous bases are classified into two types: purines and pyrimidines.
Purines are bicyclic structures (a six-membered ring fused to a five-membered ring).
Pyrimidines are monocyclic structures (a single six-membered ring).
Among the given options,$Guanine$ and $Adenine$ are purines (bicyclic).
$Thymine$,$Uracil$,and $Cytosine$ are pyrimidines (monocyclic).
Therefore,$Guanine$ is the correct answer.

(D) In nucleic acids,the nitrogenous bases are classified into two types based on their structure:
$1$. $\text{Purines}$ (bicyclic bases with two fused rings): Adenine $(A)$ and Guanine $(G)$.
$2$. $\text{Pyrimidines}$ (monocyclic bases with one ring): Cytosine $(C)$,Thymine $(T)$,and Uracil $(U)$.
Since Guanine $(G)$ is a purine,it possesses a bicyclic (double-ring) structure. Therefore,the correct answer is $G$.

(B) In the double helix structure of $DNA$,nitrogenous bases form specific base pairs through hydrogen bonding.
$Adenine$ $(A)$ pairs with $Thymine$ $(T)$ via two hydrogen bonds.
$Guanine$ $(G)$ pairs with $Cytosine$ $(C)$ via three hydrogen bonds.
Therefore,the correct pair among the options is $Adenine$ and $Thymine$.

(B) Nucleotides are joined together by a phosphodiester linkage between the $5^{\prime}$ and $3^{\prime}$ carbon atoms of the pentose sugar.

(C) nucleotide is composed of three components: a nitrogenous base (purine or pyrimidine),a pentose sugar,and ortho-phosphoric acid.
These three components are linked together to form the monomeric unit of nucleic acids.

(A) $RNA$ and $DNA$ are chiral molecules because they contain sugar units ($D$-ribose in $RNA$ and $D$-2-deoxyribose in $DNA$).
These sugar molecules possess multiple chiral carbon atoms,which impart chirality to the entire $RNA$ and $DNA$ structure.

(C) In $DNA$,the base pairing rules are based on hydrogen bonding between specific nitrogenous bases: $A$ (Adenine) pairs with $T$ (Thymine),and $G$ (Guanine) pairs with $C$ (Cytosine).
Given the sequence $G-A-T-G-C$,the complementary sequence is formed by replacing each base with its pair:
$G \rightarrow C$
$A \rightarrow T$
$T \rightarrow A$
$G \rightarrow C$
$C \rightarrow G$
Thus,the complementary chain is $CTACG...$.

(D)
In nucleic acids,the individual nucleotides are linked together through the $3'-5'$ phosphodiester bonds,which connect the $5'$ carbon atom of one sugar molecule to the $3'$ carbon atom of the next sugar molecule via a phosphate group.

(D) $DNA$ contains four bases,that is,adenine,guanine,cytosine,and thymine.
Uracil is found in $RNA$.

(A) In $DNA$,the nitrogenous bases pair specifically through hydrogen bonding.
Adenine $(A)$ always pairs with thymine $(T)$ via two hydrogen bonds.
Guanine $(G)$ always pairs with cytosine $(C)$ via three hydrogen bonds.
Therefore,the correct base pairing is $A-T$ and $G-C$.

(D) nucleoside is formed by the combination of a pentose sugar and a nitrogenous base.
Adenosine consists of the sugar ribose and the nitrogenous base adenine.
Since it lacks a phosphate group,it is classified as a nucleoside.

(B) unit formed by the attachment of a nitrogenous base to the $1^{\prime}$ position of a sugar molecule is known as a nucleoside.
In a nucleoside,the sugar carbons are numbered as $1^{\prime}, 2^{\prime}, 3^{\prime}$,etc.
Therefore,a nucleoside consists only of a sugar and a base.
Nucleotide = Sugar $+$ Base $+$ Phosphate group.

(C) The given structure is a six-membered heterocyclic ring containing two nitrogen atoms at positions $1$ and $3$,and two carbonyl groups at positions $2$ and $4$. This structure is characteristic of $Uracil$.
$Adenine$ is a purine base.
$Thymine$ is $5-methyluracil$.
$Cytosine$ contains an amino group at position $4$ and a carbonyl group at position $2$.

(D) The nitrogenous bases in $DNA$ are classified into two categories: purines and pyrimidines.
Purines are double-ring structures,which include $Adenine$ $(A)$ and $Guanine$ $(G)$.
Pyrimidines are single-ring structures,which include $Cytosine$ $(C)$ and $Thymine$ $(T)$ in $DNA$.
Therefore,the set containing a purine followed by a pyrimidine base of $DNA$ is $Adenine$ and $Cytosine$.

(C) Chargaff's rule states that in the $DNA$ of any species,the amount of guanine $(G)$ is equal to the amount of cytosine $(C)$,and the amount of adenine $(A)$ is equal to the amount of thymine $(T)$.
Statement $I$ is correct because $G = C$ in $DNA$.
Statement $II$ is incorrect because in $RNA$,adenine pairs with uracil,but there is no fixed stoichiometric rule stating their quantities must be equal in the total hydrolysate of $RNA$ as there is for $DNA$ base pairing.
Therefore,statement $I$ is correct but statement $II$ is incorrect.

(D) According to Chargaff's rule,in a double-stranded $DNA$ molecule,the amount of adenine $(A)$ is equal to the amount of thymine $(T)$,and the amount of guanine $(G)$ is equal to the amount of cytosine $(C)$.
This is because $A$ pairs with $T$ via two hydrogen bonds,and $G$ pairs with $C$ via three hydrogen bonds.
Therefore,the Assertion $(A)$ is incorrect because hydrolysis of $DNA$ yields equal amounts of $A$ and $T$,and $G$ and $C$.
The Reason $(R)$ is correct as it describes the base-pairing mechanism.
Thus,the correct option is $D$.

(A) nucleoside is formed by the attachment of a nitrogenous base to the $1'$ position of a pentose sugar through an $N$-glycosidic linkage.
As shown in the structure,the nitrogenous base is attached to the $C-1'$ carbon atom of the sugar molecule.

(A) In the given structures:
$A$ is Adenine,$B$ is Uracil,$C$ is Cytosine,and $D$ is Thymine.
Adenine $(A)$,Guanine $(G)$,and Cytosine $(C)$ are present in both $DNA$ and $RNA$.
Thymine $(T)$ is present only in $DNA$,and Uracil $(U)$ is present only in $RNA$.
Therefore,the bases present in both are Adenine $(A)$ and Cytosine $(C)$.

(A) In $DNA$,the nitrogenous bases form specific hydrogen-bonded pairs.
Adenine $(A)$ pairs with Thymine $(T)$ through two hydrogen bonds $(A=T)$.
Guanine $(G)$ pairs with Cytosine $(C)$ through three hydrogen bonds $(G \equiv C)$.
Thus,the correct representation is $G \equiv C$ and $T=A$.

(B) There are three main types of $RNA$ involved in protein synthesis: $m$-$RNA$ (messenger $RNA$),$t$-$RNA$ (transfer $RNA$),and $r$-$RNA$ (ribosomal $RNA$).
$d$-$RNA$ is not a recognized type of $RNA$.

(D) Complete hydrolysis of nucleic acids ($DNA$ or $RNA$) yields three components: a nitrogenous base,a pentose sugar (ribose or deoxyribose),and phosphoric acid $(H_3PO_4)$.

(A) According to Chargaff's rule,the amount of adenine $(A)$ is equal to the amount of thymine $(T)$,and the amount of guanine $(G)$ is equal to the amount of cytosine $(C)$ only in double-stranded $DNA$.
$m$-$RNA$,$r$-$RNA$,and single-stranded $DNA$ are single-stranded molecules.
Therefore,they do not follow Chargaff's rule and do not yield an equal number of $A$ and $T$ or $G$ and $C$ upon hydrolysis.
Thus,$(A)$,$(B)$,and $(C)$ do not give equal numbers of these bases.

(D) Watson and Crick proposed that the $DNA$ molecule is in the form of a double helix with two polynucleotide chains coiled around one another in a spiral.
This is known as $B-DNA$ or biological $DNA$.
It has $10$ nucleotide pairs per turn of the double helix and is right-handed with a diameter of $20 \mathring{A}$.
One complete turn of the double helix is $34 \mathring{A}$.
The distance between adjacent stacks or nucleotides is $3.4 \mathring{A}$.
Hence,option $(D)$ is correct.

(C) $I$. $DNA$ has a double helix structure.
$II$. Adenine forms hydrogen bonds with thymine $(A=T)$ and cytosine forms hydrogen bonds with guanine $(C \equiv G)$.
$III$. The two strands in $DNA$ molecules are complementary to each other.
$IV$. $DNA$ strand contains pentose $2$-deoxyribose sugar.
Thus,option $(C)$ is incorrect.

(C) $DNA$ is a polynucleotide chain where nucleotides are joined by phosphodiester bonds.
These bonds are strong covalent linkages between the phosphate group of one nucleotide and the sugar molecule of the adjacent nucleotide.
Specifically,the phosphate group connects the $5'$-carbon of one deoxyribose sugar to the $3'$-carbon of the next deoxyribose sugar.

(A) In $DNA$,the nitrogenous bases pair specifically through hydrogen bonds.
$G$ (guanine) pairs with $C$ (cytosine) via $3$ hydrogen bonds $(G \equiv C)$.
$A$ (adenine) pairs with $T$ (thymine) via $2$ hydrogen bonds $(A = T)$.
Therefore,the number of hydrogen bonds between guanine and cytosine is $3$,and between adenine and thymine is $2$.

(B) $RNA$ contains four nitrogenous bases:
$1$. The purines: Adenine $(A)$ and Guanine $(G)$.
$2$. The pyrimidines: Cytosine $(C)$ and Uracil $(U)$.
Both the Assertion $(A)$ and Reason $(R)$ are factually correct statements.
However,the presence of uracil in $RNA$ does not explain why adenine and guanine are purine bases.
Therefore,$(R)$ is not the correct explanation for $(A)$.

(D) In $DNA$,adenine $(A)$ pairs with thymine $(T)$ through $2$ hydrogen bonds $(A=T)$.
In contrast,guanine $(G)$ pairs with cytosine $(C)$ through $3$ hydrogen bonds $(G \equiv C)$.

(A) nucleoside is formed by the attachment of a nitrogenous base to the $1^{\prime}$ position of a pentose sugar.
Structure $(a)$ represents a pentose sugar attached to a nitrogenous base,which is the definition of a nucleoside.
Structure $(b)$ represents a nucleotide (nucleoside + phosphate group).
Structure $(c)$ represents a nitrogenous base (adenine).
Structure $(d)$ represents a pentose sugar (ribose).

(B) In the $DNA$ double helix,the nitrogenous bases pair specifically through hydrogen bonds.
Guanine $(G)$ pairs with cytosine $(C)$ via three hydrogen bonds $(G \equiv C)$.
Adenine $(A)$ pairs with thymine $(T)$ via two hydrogen bonds $(A = T)$.
Therefore,the number of hydrogen bonds between guanine and cytosine is $3$,and between adenine and thymine is $2$.

(B) The base composition of human $DNA$ varies,but the average ratio of $(A+T)/(G+C)$ in human beings is approximately $1.52$.

(B) Nucleic acids ($DNA$ and $RNA$) are composed of three main components: a pentose sugar (ribose or deoxyribose),a phosphate group (derived from phosphoric acid),and nitrogenous bases (adenine,guanine,cytosine,thymine,or uracil).
$Guanidine$ is a chemical compound with the formula $HNC(NH_2)_2$,which is not a constituent of nucleic acids.
$Guanine$ is a nitrogenous base found in nucleic acids,whereas $Guanidine$ is not.

(A) $ADP$ stands for adenosine diphosphate,which contains $2$ phosphate groups.
$ATP$ stands for adenosine triphosphate,which contains $3$ phosphate groups.
Therefore,they differ in the number of phosphate units.