Nucleic acids Questions in English

(C) Nitrogenous bases in nucleic acids are classified into two types: Purines and Pyrimidines.
Purines are double-ring structures,which include Adenine $(A)$ and Guanine $(G)$.
Pyrimidines are single-ring structures,which include Cytosine $(C)$,Thymine $(T)$,and Uracil $(U)$.
Therefore,Adenine and Guanine are purines.

(C) nucleoside consists of a nitrogenous base attached to a pentose sugar.
$A$ nucleotide consists of a nitrogenous base,a pentose sugar,and at least one phosphate group.
Therefore,the presence of a phosphate group is the fundamental difference that distinguishes a nucleotide from a nucleoside.

(B) $ATP$ stands for Adenosine Triphosphate.
It consists of an adenine base,a ribose sugar,and three phosphate groups.
Since it is a nitrogenous base attached to a sugar and phosphate groups,it is classified as a nucleotide.

(D) In a nucleic acid,two consecutive nucleotides are joined by a $3'-5'$ phosphodiester linkage.
This bond is formed between the $3'$-hydroxyl group of the sugar of one nucleotide and the $5'$-phosphate group of the next nucleotide.
This linkage creates the sugar-phosphate backbone of the polynucleotide chain.
Therefore,the correct option is $D$.

(A) nucleoside is formed by the combination of a nitrogenous base and a pentose sugar.
When a phosphate group is added to a nucleoside, it forms a nucleotide.
Therefore, the basic structure of a nucleoside is $Nitrogenous \text{ } base + Sugar$.

(D) nucleotide is the basic structural unit of nucleic acids like $DNA$ and $RNA$.
It consists of three essential components:
$1$. $A$ pentose sugar (ribose in $RNA$ or deoxyribose in $DNA$).
$2$. $A$ nitrogenous base (purine or pyrimidine).
$3$. $A$ phosphoric acid group (phosphate group).
Therefore,all the given options are correct components of a nucleotide.

(C) Adenine is a nitrogenous base found in nucleic acids like $DNA$ and $RNA$.
It belongs to the class of compounds known as purines,which are double-ring structures.
In $DNA$,adenine pairs with thymine $(T)$ via two hydrogen bonds,and in $RNA$,it pairs with uracil $(U)$.

(D) $m-RNA$ stands for messenger $RNA$ (Ribonucleic Acid).
$RNA$ is a nucleic acid composed of long chains of nucleotides.
Each nucleotide in $RNA$ consists of a ribose sugar, a phosphate group, and a nitrogenous base $(Adenine, Guanine, Cytosine, or Uracil)$.
Since these building blocks are ribonucleotides, $m-RNA$ is defined as a polymer of ribonucleotides.

(B) nucleoside is formed by the combination of a pentose sugar and a nitrogenous base.
In the case of a ribonucleoside,the pentose sugar is ribose.
Therefore,a ribonucleoside consists of a ribose sugar linked to a nitrogenous $(N_2)$ base.
When a phosphate group is added to a nucleoside,it becomes a nucleotide.

(C) Nucleotides are the building blocks of nucleic acids.
Each nucleotide consists of a nitrogenous base (purine or pyrimidine),a pentose sugar,and a phosphate group.
When many nucleotides polymerize through phosphodiester bonds,they form long chains known as polynucleotides or nucleic acids ($DNA$ and $RNA$).

(C) nucleoside is formed by the attachment of a nitrogenous base to a pentose sugar.
In both ribose and deoxyribose sugars, the nitrogenous base is linked to the $1'$ carbon atom of the sugar molecule via an $N$-glycosidic linkage.
The $5'$ carbon is typically where the phosphate group attaches to form a nucleotide, while the $2'$ carbon helps distinguish between ribose ($-OH$ group) and deoxyribose ($-H$ group).

(C) nucleotide is the basic building block of nucleic acids ($DNA$ and $RNA$).
It consists of three distinct chemical components:
$1$. $A$ nitrogenous base ($N_2$ base),which can be a purine or a pyrimidine.
$2$. $A$ pentose sugar (ribose in $RNA$ or deoxyribose in $DNA$).
$3$. $A$ phosphate group.
When these three components are linked together,they form a nucleotide. Therefore,the correct structure is $N_2$ base-sugar-phosphate.

(D) Nucleic acids,such as $DNA$ and $RNA$,are polymers of nucleotides.
Each nucleotide consists of a nitrogenous base,a phosphate group,and a pentose sugar.
In $RNA$,the pentose sugar is ribose,while in $DNA$,the pentose sugar is $2$-deoxyribose.
Among the given options,deoxyribose is a sugar specifically found in $DNA$,which is a type of nucleic acid.

(A) In nucleic acids,pyrimidine bases include Cytosine $(C)$,Thymine $(T)$,and Uracil $(U)$.
Let us analyze the number of pyrimidines in each option:
$A$: $G-A-T-C-A-A-T-C-A$ contains $T, C, T, C$ ($4$ pyrimidines).
$B$: $T-A-C-C-T-A-A-C-G$ contains $T, C, C, T, C$ ($5$ pyrimidines).
$C$: $G-C-U-A-G-A-C-A-A$ contains $C, U, C$ ($3$ pyrimidines).
$D$: $U-A-G-C-G-C-G-A-A$ contains $U, C, C$ ($3$ pyrimidines).
Therefore,the sequence containing exactly four pyrimidine bases is $G-A-T-C-A-A-T-C-A$.

(C) In biological macromolecules,specific bonds link the monomers together.
$1$. Carbohydrates are linked by $Glycosidic$ bonds.
$2$. Proteins are linked by $Peptide$ bonds.
$3$. Nucleic acids ($DNA$/$RNA$) are linked by $Phosphodiester$ bonds,not just 'Diester' bonds. While 'Diester' is a component,the specific biological term is $Phosphodiester$.
$4$. Lipids (specifically triglycerides) are linked by $Ester$ bonds.
Therefore,the option $C$ is the most inaccurate or incomplete description compared to the others.

(B) Nucleic acids,such as $DNA$ and $RNA$,are polymers of nucleotides.
Each nucleotide consists of three components: a nitrogenous base,a pentose sugar,and a phosphate group.
The chemical composition of these components involves the elements Carbon $(C)$,Hydrogen $(H)$,Oxygen $(O)$,Nitrogen $(N)$,and Phosphorus $(P)$.
Therefore,nucleic acids primarily consist of these five elements.

(B) In a polynucleotide chain,the backbone is formed by the sugar and phosphate groups.
Specifically,the $3'$-carbon of one pentose sugar $(C_5H_{10}O_5)$ is linked to the $5'$-carbon of the adjacent pentose sugar through a phosphate group.
This linkage involves two ester bonds,one with each sugar,and is therefore known as a phosphodiester bond.
Thus,the correct answer is $B$.

(B) Nitrogenous bases are organic molecules that contain nitrogen and act as bases in chemical reactions.
In biological systems,these bases (purines and pyrimidines) are heterocyclic compounds,meaning they contain a ring structure consisting of carbon and nitrogen atoms.
Therefore,nitrogenous bases possess a cyclic structure.

(B) The structural formula provided shows a pyrimidine ring with a methyl group $(-CH_3)$ attached at the $5^{th}$ position. This specific structure is characteristic of Thymine ($5$-methyluracil). Uracil lacks this methyl group,while Cytosine has an amino group instead of a carbonyl group at the $4^{th}$ position. Guanine is a purine,which has a double-ring structure. Therefore,the correct answer is Thymine.

(D) The provided structural formula represents a purine derivative.
Specifically,it shows a double-ring structure characteristic of purines with an amino group $(-NH_2)$ attached at the $6^{th}$ position.
This specific structure is Adenine.
Cytosine,Thymine,and Uracil are pyrimidines (single-ring structures),while Guanine is another purine but contains a carbonyl group $(=O)$ and an amino group $(-NH_2)$ at different positions.

(D) The chemical structure shown is phosphoric acid $(H_3PO_4)$.
In a nucleotide,the phosphate group is attached to the $5'$ carbon atom of the pentose sugar via a phosphoester bond.
This linkage forms the backbone of the nucleic acid chain.

(C) Thymine ($5$-methyluracil) is a pyrimidine nucleobase.
The chemical structure of thymine consists of a heterocyclic ring with two carbonyl groups $(C=O)$ and one carbon-carbon double bond $(C=C)$ within the ring.
Specifically,there are two $C=O$ double bonds and one $C=C$ double bond.
Therefore,the total number of double bonds in the thymine molecule is $2 + 1 = 3$.

(B) $1$. Pyrimidines (Cytosine,Thymine,and Uracil) are heterocyclic aromatic organic compounds similar to pyridine,containing two nitrogen atoms at positions $1$ and $3$ of the six-membered ring. Thus,Assertion $A$ is true.
$2$. $DNA$ contains Adenine,Guanine,Cytosine,and Thymine. Uracil $(U)$ is found in $RNA$ instead of Thymine. Therefore,$DNA$ does not contain $U$. Thus,Reason $R$ is true.
$3$. While both statements are scientifically correct,the fact that $DNA$ does not contain $U$ is not the reason why pyrimidines have a single-ring structure. Therefore,$R$ is not the correct explanation of $A$.

(B) The given reaction shows the condensation of two nucleotides.
In the reaction,the $3'$-$OH$ group of one nucleotide reacts with the $5'$-phosphate group of another nucleotide.
This results in the formation of a phosphodiester bond (indicated by '$A$' in the diagram).
The linkage of two nucleotides via a phosphodiester bond results in the formation of a dinucleotide.
Therefore,the correct option is $(B)$.

(C) The provided image shows the formation of a dinucleotide from two nucleotides. The reaction involves the removal of a water molecule $(H_2O)$ between the $3'-OH$ group of one nucleotide and the phosphate group attached to the $5'-CH_2$ of the adjacent nucleotide. The resulting linkage formed between the phosphate group and the sugar molecules is known as a phosphodiester bond. Therefore,$A$ represents the phosphodiester bond.

(A) The given structure consists of a nitrogenous base (Adenine) attached to a pentose sugar (Ribose).
$1$. $A$ nucleoside is formed by the combination of a nitrogenous base and a pentose sugar.
$2$. The sugar shown in the structure has an $-OH$ group at the $2'$ position,which identifies it as ribose sugar.
$3$. Since there is no phosphate group attached,it is not a nucleotide (ribotide or deoxyribotide).
$4$. Therefore,the structure represents a nucleoside,specifically Adenosine.

(B) The given figure shows a nitrogenous base (adenine) attached to a ribose sugar,which is further attached to a phosphate group.
$1$. $A$ nitrogenous base + sugar = Nucleoside.
$2$. $A$ nitrogenous base + sugar + phosphate group = Nucleotide.
$3$. Since the sugar has two hydroxyl $(-OH)$ groups at the $2'$ and $3'$ positions,it is a ribose sugar,making the entire structure a ribonucleotide.

(D) The provided figure shows an Adenosine Monophosphate $(AMP)$ molecule. It consists of an adenine base,a ribose sugar,and a phosphate group. The presence of the hydroxyl $(-OH)$ group at the $2'$ position of the ribose sugar confirms that it is a ribonucleotide. Adenosine monophosphate is a fundamental building block of $RNA$ (Ribonucleic Acid). Therefore,it plays an important role in the formation of $RNA$.

(B) phosphodiester bond is a chemical bond that joins the $3'$ carbon atom of one sugar molecule and the $5'$ carbon atom of another in a nucleic acid chain ($DNA$ or $RNA$).
- In a polypeptide,amino acids are linked by peptide bonds.
- In a diglyceride,fatty acids are linked to glycerol by ester bonds.
- In a polysaccharide,monosaccharides are linked by glycosidic bonds.
- Nucleic acids (polynucleotides) are formed by linking nucleotides through phosphodiester bonds.
Therefore,the correct option is $B$.

(A) Uridine is a nucleoside formed by the combination of a nitrogenous base (Uracil) and a pentose sugar (Ribose).
$A$ nucleoside consists of a pentose sugar and a nitrogenous base,lacking the phosphate group.
Since Uridine is composed of Uracil and Ribose,it is classified as a nucleoside.
Uracil + Ribose $\to$ Uridine.

(D) nucleoside is formed by the linkage of a nitrogenous base with a pentose sugar through an $N$-glycosidic linkage.
Uridine is a nucleoside formed specifically by the combination of the pyrimidine base $Uracil$ and a $Ribose$ sugar (which is a pentose sugar).
Therefore,when uracil joins with a pentose sugar,it forms uridine.

(C) Phosphorus is a vital macro-nutrient for plants.
It is a constituent of cell membranes,all nucleic acids ($DNA$ and $RNA$),and nucleotides (such as $ATP$).
Ribosomes are composed of ribosomal $RNA$ (rRNA) and proteins; since rRNA contains phosphorus,ribosomes also contain phosphorus.
Therefore,phosphorus is present in nucleotides and ribosomes.

(C) Heterocyclic rings are ring structures that contain at least one atom other than carbon within the ring,such as nitrogen,oxygen,or sulfur.
In biological systems,nitrogen bases (purines and pyrimidines) are classic examples of heterocyclic compounds.
Purines (like adenine and guanine) consist of a fused pyrimidine and imidazole ring,both of which are heterocyclic.
Pyrimidines (like cytosine,thymine,and uracil) consist of a single heterocyclic ring containing two nitrogen atoms.
Proteins and amino acids contain nitrogen,but the nitrogen is typically part of the amino or amide groups,not part of a heterocyclic ring structure (except for specific amino acids like histidine,proline,and tryptophan).
Lipids generally consist of long hydrocarbon chains or fused carbon rings (like steroids) and do not typically contain heterocyclic rings.

(C) nucleotide is the basic structural unit of nucleic acids ($DNA$ and $RNA$).
It consists of three chemically distinct components:
$1$. $A$ nitrogenous base (either a purine or a pyrimidine).
$2$. $A$ pentose sugar (a monosaccharide,specifically ribose or deoxyribose).
$3$. $A$ phosphate group (derived from phosphoric acid).
Therefore,option $C$ correctly identifies these components.

(D) Nucleic acids,such as $DNA$ and $RNA$,are long-chain polymers composed of repeating units called nucleotides.
Each nucleotide consists of three components: a nitrogenous base,a pentose sugar (ribose or deoxyribose),and a phosphate group.
Therefore,nucleic acids are defined as polynucleotides.

(D) nucleoside consists of a nitrogenous base attached to a pentose sugar.
Nucleotides,on the other hand,consist of a nitrogenous base,a pentose sugar,and a phosphate group.
$1$. Cytidylic acid,Guanylic acid,and Uridylic acid are all nucleotides because they contain a phosphate group.
$2$. Thymidine is a nucleoside formed by the combination of the nitrogenous base Thymine and the sugar Deoxyribose.
Therefore,the correct answer is $D$.

(C) nucleoside is formed by the combination of a nitrogenous base and a pentose sugar.
Nucleotides are formed when a phosphate group is added to a nucleoside.
$1$. Thymidine is a nucleoside,but guanilic acid is a nucleotide.
$2$. Arachidonic acid is a fatty acid,and phospholipid is a lipid.
$3$. Guanosine (guanine + ribose) and adenosine (adenine + ribose) are both nucleosides.
$4$. Thymidylic acid and cytidylic acid are both nucleotides.
Therefore,the correct option is $C$.

(C) The chemical formula $C_5H_{10}O_4$ represents deoxyribose sugar.
Deoxyribose is a pentose sugar that lacks one oxygen atom compared to ribose $(C_5H_{10}O_5)$.
$DNA$ (Deoxyribonucleic acid) contains deoxyribose sugar as its backbone component.
$RNA$ (Ribonucleic acid) contains ribose sugar $(C_5H_{10}O_5)$.
Starch and Amylase are polymers of glucose and amino acids,respectively,and do not contain this specific pentose sugar structure.

(C) Nitrogenous bases are classified into two types: Purines and Pyrimidines.
$1$. Purines are double-ring structures,which include Adenine $(A)$ and Guanine $(G)$.
$2$. Pyrimidines are single-ring structures,which include Cytosine $(C)$,Thymine $(T)$,and Uracil $(U)$.
Comparing the options:
- Option $A$: Cytosine is a Pyrimidine,so this is incorrect.
- Option $B$: Adenine is a Purine,so this is incorrect.
- Option $C$: Guanine is a Purine,which is correct.
Therefore,the correct pair is Purine nitrogen base - Guanine.

(B) Nucleic acids,such as $DNA$ and $RNA$,are polymers composed of repeating units called nucleotides.
Each nucleotide consists of three components: a nitrogenous base,a pentose sugar (ribose or deoxyribose),and a phosphate group.
Peptides are components of proteins,polysaccharides are polymers of monosaccharides (carbohydrates),and fatty acids with glycerol are components of lipids.

(B) Nucleic acids,such as $DNA$ and $RNA$,are complex polymers of nucleotides.
They exhibit a wide variety of secondary structures.
The most famous example is the $DNA$ double helix,which is a secondary structure proposed by Watson and Crick.
These structures are stabilized by hydrogen bonding between complementary base pairs.

(B) nucleoside is formed by the combination of a nitrogenous base and a pentose sugar.
Thymidine is formed by the combination of the nitrogenous base $Thymine$ and the sugar $Deoxyribose$.
Since it lacks a phosphate group,it is classified as a nucleoside.
In contrast,a nucleotide contains a nitrogenous base,a pentose sugar,and a phosphate group (e.g.,Thymidylic acid).

(A) nucleoside is a biochemical compound consisting of a nitrogenous base ($N$-base) covalently attached to a sugar molecule (pentose sugar,either ribose or deoxyribose) via an $N$-glycosidic linkage.
When a phosphate group is added to a nucleoside,it becomes a nucleotide.
Therefore,the correct option is $A$.

(C) nucleotide is the basic structural unit of nucleic acids like $DNA$ and $RNA$.
It consists of three main components:
$1$. $A$ nitrogenous base (either a purine or a pyrimidine).
$2$. $A$ pentose sugar (deoxyribose in $DNA$ or ribose in $RNA$).
$3$. $A$ phosphate group.
Therefore,the correct composition of a nucleotide is a nitrogenous base,a sugar,and a phosphate group.

(D) The basic structural unit of a nucleic acid (such as $DNA$ or $RNA$) is the $Nucleotide$.
Each $Nucleotide$ consists of three components: a nitrogenous base,a pentose sugar (ribose or deoxyribose),and a phosphate group.
While a $Nucleoside$ consists only of a nitrogenous base and a pentose sugar,the addition of a phosphate group converts it into a $Nucleotide$,which acts as the monomeric building block for nucleic acid polymers.

(A) Adenine is a nitrogenous base found in $DNA$ and $RNA$.
Nitrogenous bases are classified into two categories: Purines and Pyrimidines.
Purines include Adenine $(A)$ and Guanine $(G)$,which are double-ring structures.
Pyrimidines include Cytosine $(C)$,Thymine $(T)$,and Uracil $(U)$,which are single-ring structures.
Therefore,Adenine is a Purine.

(C) In $\beta-DNA$ (the standard Watson-Crick model),one full turn of the helix is $34 \ \mathring{A}$ long,not $45 \ \mathring{A}$.
Therefore,the statement in option $C$ is incorrect.
- Some viruses (e.g.,$\phi X174$) contain single-stranded $DNA$.
- $RNA$ can be double-stranded in certain viruses (e.g.,Reovirus).
- $Z-DNA$ is a left-handed helix with $12$ base pairs per turn.

(D) In a nucleic acid chain,individual nucleotides are linked together to form a polynucleotide chain.
This linkage occurs between the $3'$-carbon atom of the sugar moiety of one nucleotide and the $5'$-carbon atom of the sugar moiety of the adjacent nucleotide.
The bond formed by this linkage is known as a $3'-5'$ phosphodiester bond.
Therefore,the correct option is $D$.

(A) $ATP$ stands for Adenosine Triphosphate.
It consists of an adenine base,a ribose sugar,and three phosphate groups.
Because it contains a nitrogenous base,a pentose sugar,and phosphate groups,it is classified as a nucleotide.
$A$ nucleoside consists only of a nitrogenous base and a sugar,whereas a nucleotide includes the phosphate group as well.

(A) nucleotide is the fundamental monomeric unit of nucleic acids ($DNA$ and $RNA$). Each nucleotide consists of three distinct chemical components:
$1$. $A$ nitrogenous base (purine or pyrimidine).
$2$. $A$ pentose sugar (ribose in $RNA$ or deoxyribose in $DNA$).
$3$. $A$ phosphate group.
These three components are linked together to form a single nucleotide unit. Therefore, the correct composition is Base - Sugar - Phosphate.