Nucleic Acids Questions in English

(A) In $DNA$,the nitrogenous base pairs are held together by hydrogen bonds.
Adenine $(A)$ pairs with Thymine $(T)$ via $2$ hydrogen bonds,and Guanine $(G)$ pairs with Cytosine $(C)$ via $3$ hydrogen bonds.
These hydrogen bonds provide stability to the double-helical structure of $DNA$.

(D) The correct answer is $D$.
$A$ nucleotide is composed of three components: a nitrogenous base,a pentose sugar,and a phosphate group.
The combination of a nitrogenous base and a sugar is known as a nucleoside.
Therefore,$\text{Nucleotide} = \text{Nucleoside} + \text{Phosphate} = (\text{Nitrogen base} + \text{Sugar}) + \text{Phosphate}$.

(A) $DNA$ (deoxyribonucleic acid) is the primary hereditary material in humans and almost all other organisms.
It carries the genetic instructions necessary for the development,functioning,growth,and reproduction of organisms.
The information in $DNA$ is stored as a code made up of four chemical bases: adenine $(A)$,guanine $(G)$,cytosine $(C)$,and thymine $(T)$.

(C) Adenine is a purine base that is present in both $DNA$ and $RNA$ as a fundamental component of nucleotides.

(C) In a $DNA$ molecule,nucleotides are linked together by phosphodiester bonds.
Specifically,the $3'$-hydroxyl group of the pentose sugar of one nucleotide is linked to the $5'$-phosphate group of the next nucleotide.
Thus,the phosphate group of one unit connects to the pentose sugar of another unit.

(D) $RNA$ is composed of ribonucleotides.
Each ribonucleotide consists of a pentose sugar (ribose),a nitrogenous base ($Adenine$,$Guanine$,$Uracil$,or $Cytosine$),and a $Phosphate$ group.
$Pyridine$ is a heterocyclic organic compound and is not a constituent of $RNA$.

(C) $ATP$ stands for $Adenosine$ $Triphosphate$.
The structure of $ATP$ consists of an $Adenine$ base,a ribose sugar,and three phosphate groups.
Therefore,$Adenine$ is the nitrogenous base found in $ATP$.

(D) Guanidine is not present in nucleic acid. The four main nitrogenous bases found in nucleic acids are Cytosine,Adenine,Thymine,and Guanine.
Adenine and Guanine are purines,while Thymine and Cytosine are pyrimidines.
These bases,along with sugar and phosphate,form the components of $DNA$.
Guanidine is a distinct chemical compound with the formula $CH_5N_3$.

(B) Nucleic acids ($DNA$ and $RNA$) contain nitrogenous bases such as Adenine,Guanine,Cytosine,Thymine,and Uracil.
$2-$aminopyridine is an organic compound with the formula $H_2NC_5H_4N$ and is not a component of nucleic acids.
Adenine and Guanine are purines,while Thymine,Cytosine,and Uracil are pyrimidines.

(D) Nucleic acids are polymers of nucleotides. Each nucleotide consists of a nitrogenous base,a pentose sugar,and a phosphate group.
In the structure of a nucleic acid,the backbone is formed by the alternating sequence of sugar and phosphate groups,while the nitrogenous bases are attached to the sugar units.
Therefore,the repeating unit in the backbone is sugar-phosphate,with the base attached to the sugar. Among the given options,the sequence of components in a nucleotide unit is often represented as sugar-phosphate-base (where the base is attached to the sugar). However,if referring to the backbone chain specifically,it is sugar-phosphate. Given the options provided,$D$ is the most appropriate representation of the structural arrangement.

(D) The segment of $DNA$ that acts as the instructional manual for the synthesis of a protein is called a $Gene$.
Every protein in a cell is encoded by a specific $Gene$.

(A) The $3-dimensional$ double helical structure of $DNA$ was proposed by James Watson and Francis Crick in $1953$.

(C) The segment of $DNA$ molecules which codes or specifies for one polypeptide chain is called a gene.
$A$ gene is the basic physical and functional unit of heredity.
Genes,which are made up of $DNA$,act as instructions to make proteins.
They hold the information to build and maintain an organism's cells and pass genetic characters to offspring.

(C) $DNA$ has a double-helical structure.Its two strands are complementary to each other.Both strands of $DNA$ are antiparallel to one another.

(A) gene is defined as a specific segment of a $DNA$ molecule that contains the instructions to code for a particular protein or functional $RNA$ molecule.

(A) The sugar present in $DNA$ is $2$-deoxy-$D$-ribose,commonly known as deoxyribose.
It contains one less hydroxyl group at the $2'$-position compared to the ribose sugar found in $RNA$.

(D) $DNA$ contains the nitrogenous base Thymine $(T)$,whereas $RNA$ contains Uracil $(U)$ in its place.
Therefore,the base present in $DNA$ but not in $RNA$ is Thymine.

(A) Mutation is a chemical change in the sequence of nitrogenous bases along the $DNA$ strand,which can lead to the synthesis of a protein with an altered amino acid sequence.

(A) The nitrogenous bases found in nucleic acids are classified into two types: purines and pyrimidines.
Purines consist of a bicyclic structure (a six-membered ring fused to a five-membered ring),which includes $Adenine$ and $Guanine$.
Pyrimidines consist of a single six-membered ring,which includes $Cytosine$,$Thymine$,and $Uracil$.
Therefore,$Guanine$ is a purine derivative.

(B) $DNA$ contains $2$-deoxyribose sugar and the nitrogenous base thymine $(T)$.
$RNA$ contains ribose sugar and the nitrogenous base uracil $(U)$ instead of thymine.
Therefore,$RNA$ is characterized by the presence of ribose sugar and uracil.

(D) $DNA$ performs the following primary functions in an organism:
$(i)$ It acts as the template for the synthesis of $RNA$ molecules (transcription).
$(ii)$ It stores and transmits genetic information regarding heredity characteristics from one generation to the next.
$(iii)$ It provides the coded instructions necessary for the synthesis of proteins and polypeptides (translation).
Therefore,all of the given options are correct functions of $DNA$.

(B) codon is a sequence of three nucleotides in $m-RNA$ that codes for a specific amino acid during protein synthesis.
$t-RNA$ contains the anticodon,which is complementary to the codon on $m-RNA$.

(C) Nucleic acid is a polymer of nucleotides.
Nucleotides are the monomeric units that link together through phosphodiester bonds to form long chains of nucleic acids,such as $DNA$ and $RNA$.

(B) An alteration in the base sequence of a nucleic acid molecule is called a mutation.
This can be caused by factors such as radioactive rays,chemical mutagens,or errors during $DNA$ replication.

(C) $Guanine$ is the nucleic acid base that possesses two possible binding sites for hydrogen bonding in the context of base pairing,specifically involving the $N-H$ group and the carbonyl oxygen or nitrogen atoms.

(B) According to Chargaff's rule,the $DNA$ of any species from any organism should have a $1:1$ stoichiometric ratio of purine and pyrimidine bases.
Specifically,the amount of adenine $(A)$ is equal to that of thymine $(T)$,and the amount of guanine $(G)$ is equal to that of cytosine $(C)$.
Therefore,the correct option is $(B)$.

(D) The process of $DNA$ multiplication is known as replication.
During this process,a $DNA$ molecule makes an exact copy of itself.

(B) Nucleic acids contain two types of nitrogenous bases: purines and pyrimidines.
$1$. Purines include Adenine $(A)$ and Guanine $(G)$.
$2$. Pyrimidines include Cytosine $(C)$,Thymine $(T)$,and Uracil $(U)$.
Therefore,Guanine is a purine,not a pyrimidine.

(D) Nucleic acids contain two types of nitrogenous bases: purines and pyrimidines.
$1$. Purines include $Adenine$ and $Guanine$.
$2$. Pyrimidines include $Cytosine$,$Thymine$,and $Uracil$.
$Caffeine$ is a xanthine alkaloid,which is a derivative of purine,but it is not one of the standard nitrogenous bases found in nucleic acids.
However,among the given options,$Cytosine$ is a pyrimidine,not a purine. Therefore,$Cytosine$ is the correct answer as it is a pyrimidine.

(A) $DNA$ contains the bases adenine,guanine,cytosine,and thymine.
$RNA$ contains the bases adenine,guanine,cytosine,and uracil.
Therefore,uracil is present in $RNA$ but absent in $DNA$.

(C) $DNA$ (Deoxyribonucleic acid) contains four nitrogenous bases: Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Thymine $(T)$.
These bases are classified into two categories: Purines and Pyrimidines.
Purines include Adenine $(A)$ and Guanine $(G)$.
Pyrimidines include Cytosine $(C)$ and Thymine $(T)$.
Therefore,the pyrimidine bases present in $DNA$ are Cytosine and Thymine.

(B) Nucleic acids ($DNA$ and $RNA$) are composed of three main components: a pentose sugar (ribose or deoxyribose),a nitrogenous base (adenine,guanine,cytosine,thymine,or uracil),and phosphoric acid. $Guanidine$ is not a constituent of nucleic acids.

(B) In $DNA$ molecules,the nitrogenous bases pair specifically according to Chargaff's rules.
Adenine $(A)$ always pairs with Thymine $(T)$ via two hydrogen bonds.
Guanine $(G)$ always pairs with Cytosine $(C)$ via three hydrogen bonds.
Therefore,the complementary base pairs are $A-T$ and $G-C$.

(A) 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 correct answer is $Uracil$.

(C) Adenine $(A)$ is a purine base that serves as a fundamental component of nucleic acids. It is present in both $DNA$ (deoxyribonucleic acid) and $RNA$ (ribonucleic acid),where it forms base pairs with thymine $(T)$ in $DNA$ and uracil $(U)$ in $RNA$.

(B) $DNA$ stands for Deoxyribonucleic acid and $RNA$ stands for Ribonucleic acid.
In $RNA$,the sugar is ribose,which has an $-OH$ group at the $2'$-carbon position.
In $DNA$,the sugar is $2$-deoxyribose,which lacks the $-OH$ group at the $2'$-carbon position (it has only an $-H$ atom there).
Therefore,the difference in the sugar structure is at the $2'$-carbon atom.

(D) In $DNA$ (Deoxyribonucleic acid),the sugar is $2$-deoxyribose,which lacks a hydroxyl $(-OH)$ group at the $2^{nd}$ carbon position.
In $RNA$ (Ribonucleic acid),the sugar is ribose,which contains a hydroxyl $(-OH)$ group at the $2^{nd}$ carbon position.
Therefore,the structural difference between the sugars of $DNA$ and $RNA$ is at the $2^{nd}$ carbon atom.

(C) The double-helical structure of $DNA$ is stabilized primarily by hydrogen bonding between the complementary nitrogenous bases ($Adenine$ with $Thymine$ and $Guanine$ with $Cytosine$).
These hydrogen bonds hold the two strands of the $DNA$ double helix together.

(A) In the structure of $DNA$,the nitrogenous bases follow Chargaff's rule of base pairing.
According to this rule,Adenine $(A)$ always pairs with Thymine $(T)$ via two hydrogen bonds,and Guanine $(G)$ always pairs with Cytosine $(C)$ via three hydrogen bonds.
Therefore,the correct base pairing is $A - T$ and $G - C$.

(C) In the structure of nucleotides,which are the building blocks of $DNA$ and $RNA$,the sugar molecule is a pentose sugar (deoxyribose or ribose).
The heterocyclic nitrogenous base is attached to the $C_1$ position of the sugar via an $N$-glycosidic linkage.
The phosphate group is attached to the $C_5$ position of the sugar via a phosphoester linkage.
Therefore,the base is at $C_1$ and the phosphate ester is at $C_5$.

(B) $DNA$ contains the nitrogenous bases Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Thymine $(T)$.
$RNA$ contains the nitrogenous bases Adenine $(A)$,Guanine $(G)$,Cytosine $(C)$,and Uracil $(U)$.
Comparing both,the common bases present in both $DNA$ and $RNA$ are Adenine,Guanine,and Cytosine.

(D) $DNA$ contains the nitrogenous base $Thymine$ $(5-methyluracil)$,whereas $RNA$ contains $Uracil$ in its place. Therefore,$Thymine$ is the base present in $DNA$ but not in $RNA$.

(B) The double-helix structure of $DNA$ was proposed by James Watson and Francis Crick in $1953$. This model explains the base pairing and the helical nature of the $DNA$ molecule.

(A) In a polynucleotide chain,a phosphodiester linkage is formed between the $3'$-$OH$ group of the pentose sugar of one nucleotide and the $5'$-phosphate group of the adjacent nucleotide.
Therefore,the linkage involves the $3'$ carbon of one sugar and the $5'$ carbon of the other.

(C) In nucleic acids ($DNA$ and $RNA$),the fundamental unit is a nucleotide.
$A$ nucleotide consists of three components: a nitrogenous base,a pentose sugar (ribose or deoxyribose),and a phosphate group.
The nitrogenous base is attached to the $1'$ position of the sugar,and the phosphate group is attached to the $5'$ position of the sugar.
Thus,the structural sequence in a nucleotide unit is $Base-Sugar-Phosphate$.

(A) In the structure of $DNA$,the two strands are held together by hydrogen bonds between the complementary nitrogenous bases. Adenine $(A)$ pairs with Thymine $(T)$ via two hydrogen bonds,and Guanine $(G)$ pairs with Cytosine $(C)$ via three hydrogen bonds.

(A) In nucleic acids,a unit consisting of a nitrogenous base,a pentose sugar,and a phosphate group is known as a $Nucleotide$.
$A$ $Nucleoside$ consists only of a nitrogenous base attached to a pentose sugar.

(C) In $DNA$,nucleotides are linked together by phosphodiester bonds.
Specifically,the $5'$-phosphate group of one nucleotide is linked to the $3'$-hydroxyl group of the pentose sugar of the next nucleotide.
This forms the sugar-phosphate backbone of the $DNA$ strand.

(D) The process of $DNA$ duplication or copying is known as $Replication$.