Q.DNA and RNA are similar with respect to
Concept understanding — Properties of Genetic Material (DNA vs RNA)
Any candidate genetic material must satisfy three properties: self-replication, structural and chemical stability, and the ability to mutate, while also being expressible as observable characters. Both DNA and RNA can self-replicate via complementary base pairing, which proteins cannot do at all. DNA is markedly more stable than RNA because every RNA nucleotide carries a reactive 2'-OH group that DNA's deoxyribose lacks, making RNA more chemically reactive and prone to degradation; DNA's use of thymine instead of uracil adds further stability, and because DNA is double-stranded and complementary, damaged DNA can often be repaired or renatured after denaturation, a resilience RNA generally lacks. Both nucleic acids can mutate, but RNA's greater instability means it mutates, and therefore evolves, faster than DNA, which is why RNA viruses with short life spans tend to evolve rapidly. RNA can be translated into protein directly and so expresses Mendelian characters immediately, whereas DNA always depends on RNA as an intermediary. This division of labour explains why DNA, the more stable molecule, is used for long-term genetic storage, while RNA, more versatile and directly translatable, is used to transfer that information into action.
DNA and RNA are both nucleic acids, so both are built from nucleotides containing a sugar, a nitrogenous base and a phosphate.
(c) Nucleotide containing sugars, nitrogen bases and phosphates
Step 1. DNA has thymine and no uracil; RNA has uracil and no thymine -- so (a) is a difference, not a similarity.
Step 2. DNA is double-stranded (a helix of two strands); RNA is normally single-stranded -- so (b) is also a difference.
Step 3. The mRNA codon for phenylalanine is UUU, but DNA has no U at all, so (d) is meaningless as a similarity between the two molecules.
Step 4. What DNA and RNA do share is their basic chemical architecture: both are polymers of nucleotides, and every nucleotide in either molecule is built from a pentose sugar, a nitrogenous base and a phosphate group.
DNA and RNA are similar in that both are built from (c) nucleotides containing sugars, nitrogen bases and phosphates.
Check each option against the known chemical differences between DNA and RNA (sugar, strandedness, bases) to find the one true shared feature.
- Picking thymine as shared, forgetting DNA has thymine while RNA has uracil instead.
- Assuming both are single-stranded, when only RNA typically is.
Showing the 12 most recent of 14 on this concept.
- CBSE 2026Set BOTANY1 markMCQQ.Genes are made up of _____.(a) protein(b) DNA(c) amino acids(d) nucleosides
›Reveal solutionSolution
A gene is a discrete segment of DNA that codes for a functional product (usually a polypeptide or RNA); DNA, not protein or free amino acids, is the hereditary material.
Early biologists debated whether protein or DNA was the genetic material, since proteins seemed structurally more complex. This was settled by a series of classic experiments: Griffith's transformation experiment in pneumococcus (1928) showed a "transforming principle" could convert harmless bacteria into virulent ones; Avery, MacLeod and McCarty (1944) showed this transforming principle was specifically DNA (destroyed only by DNase, not by protease or RNase); and the Hershey-Chase blender experiment (1952) with radioactively labelled bacteriophages confirmed that only the phage's DNA (labelled with ³²P), not its protein coat (labelled with ³⁵S), entered the bacterium and directed the production of new phages. Together these experiments established DNA as the genetic material. A gene is therefore a specific stretch of this DNA - a sequence of nucleotides (each nucleotide made of a nitrogenous base, a deoxyribose sugar, and a phosphate group) - that carries the coded instructions for making an RNA/protein product. Proteins and amino acids are the products of gene expression, not the genetic material itself, and nucleosides (base + sugar, without phosphate) are only components of the nucleotides that make up DNA.
✓Final answer(b) DNA - genes are functional segments of the DNA molecule, which is the hereditary material of the cell.
- CBSE 2026Set ANNUAL1 markMCQQ.Which one of the following will not allow a molecule to act as a genetic material ?(a) Ability to generate its replication(b) Ability to mutate(c) Ability to express itself in the form of Mendelian character(d) Ability to easily break down structurally and chemically
›Reveal solutionSolution
A genetic material must be chemically and structurally STABLE (not easily degraded) so that it can be faithfully copied and passed on across generations.
For a molecule to qualify as genetic material it needs: (a) the ability to replicate itself, (b) chemical and structural stability, (c) the ability to mutate (a slow rate of change is needed to provide variation for evolution), and (d) the ability to express itself as Mendelian characters. A molecule that easily breaks down structurally and chemically would fail to reliably store and transmit hereditary information across generations, so it cannot serve as genetic material.
✓Final answerOption (d): Ability to easily break down structurally and chemically — this is a property genetic material must NOT have.
- CBSE 2025Set A1 markQ.Write True / False: Nucleic acid are long polymers of nucleotides.
›Reveal solutionSolution
The statement is True: nucleic acids are polymers built from many nucleotide monomers linked together.
A nucleotide is the basic structural unit (monomer) of a nucleic acid, made of a nitrogenous base, a pentose sugar, and a phosphate group. Many nucleotides join together through phosphodiester bonds (between the 3'-OH of one sugar and the 5'-phosphate of the next) to form a long chain called a polynucleotide. Both DNA (a double-stranded polynucleotide, usually very long) and RNA (usually single-stranded) are, by this definition, long polymers of nucleotides — making the given statement correct.
✓Final answerTrue.
- CBSE 2025Set ANNUAL1 markMCQQ.As compared to DNA, RNA is chemically(a) Equally reactive and stable(b) Less reactive and more stable(c) More reactive and less stable(d) More reactive and more stable
›Reveal solutionSolution
Compared to DNA, RNA is chemically more reactive (due to the 2'-OH group on ribose) and less stable (usually single-stranded and prone to hydrolysis), which is why DNA - not RNA - serves as the primary long-term genetic material in most organisms.
DNA contains deoxyribose sugar, which lacks a hydroxyl group at the 2' carbon; this makes the DNA backbone chemically less reactive and more resistant to hydrolysis. DNA is also usually double-stranded (a stable double helix held together by complementary base pairing and stacking interactions), further adding to its structural stability. RNA, on the other hand, contains ribose sugar with a reactive 2'-OH group, making its phosphodiester backbone more susceptible to hydrolytic cleavage; RNA is also typically single-stranded, so it lacks the protective double-helical structure. Together these make RNA more reactive and less stable, which is one reason DNA (not RNA) evolved as the stable, long-term repository of genetic information.
✓Final answer(c) More reactive and less stable.
- CBSE 2025Set ANNUAL1 markMCQQ.Assertion (A) : Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) are the two types of nucleic acids found in living systems. Reason (R) : RNA acts as the genetic material in most of the organisms.(a) Assertion (A) and Reason (R) both are true and Reason (R) is the correct explanation of Assertion (A).(b) Assertion (A) and Reason (R) both are true, but Reason (R) is not the correct explanation of Assertion (A).(c) Assertion (A) is true, but Reason (R) is false.(d) Assertion (A) and Reason (R) both are false.
›Reveal solutionSolution
DNA and RNA are indeed the two nucleic acids (A is true), but DNA — not RNA — is the genetic material in most organisms (R is false).
Assertion (A) is correct: living systems contain two types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). However, Reason (R) is incorrect: DNA is the genetic material in the vast majority of organisms (all cellular life and most viruses), because its double-stranded, chemically more stable structure (due to the absence of the reactive 2'-OH group and the presence of thymine instead of uracil) makes it better suited for accurate, long-term storage and transmission of genetic information. RNA serves as the genetic material only in certain viruses (e.g. retroviruses, TMV), which is the exception rather than the rule.
✓Final answer(c) Assertion (A) is true, but Reason (R) is false.
- CBSE 2025Set ANNUAL1 markMCQQ.Why do species of bacteria and humans have their DNA analyzed using the same fundamental methods ?(a) Every cell in every creature is identical(b) Every organism has the same quantity of DNA(c) All creatures have the same DNA sequence(d) All organisms have the same basic DNA structure
›Reveal solutionSolution
DNA analysis works identically across all life because every organism's DNA shares the same fundamental double-helical structure and four-base chemistry.
DNA is universal in its chemistry: in bacteria and humans alike it is a double helix built from the same four nitrogenous bases (adenine, guanine, cytosine, thymine) linked via a sugar-phosphate backbone, following the same base-pairing rules (A-T, G-C). Because the molecule's physical and chemical structure is identical across species, the same extraction, restriction digestion, electrophoresis, PCR and sequencing methods work on any organism's DNA. This is not because organisms have identical DNA sequences, identical quantities of DNA, or identical cells (options a, b, c are false) — sequences and genome sizes vary enormously between species; only the underlying structural chemistry is shared.
✓Final answer(d) All organisms have the same basic DNA structure.
- CBSE 2024Set 57/2/11 markMCQQ.For Questions number 13 to 16, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : RNA is unstable and can mutate at a faster rate. Reason (R) : The presence of 2' – OH group in every nucleotide of RNA makes it labile and easily degradable.
›Reveal solutionSolution
The key idea is that the 2'–OH group in RNA makes it chemically reactive and prone to hydrolysis, which explains both its instability and faster mutation rate. The correct answer is (A).
Concept and Intuition
The question tests your understanding of the fundamental chemical difference between RNA and DNA — and how that difference drives biological consequences. The 2'–OH group in RNA is not just a structural detail; it’s the reason RNA is more reactive, less stable, and mutates faster than DNA. Think of it this way: DNA is like a sturdy, well-protected library book (stable, rarely damaged), while RNA is like a working draft on loose paper (easily torn, frequently revised). The 2'–OH group is the chemical “weak spot” that makes RNA labile.
Step-by-Step Reasoning
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Examine the Assertion (A): “RNA is unstable and can mutate at a faster rate.”
This is a well-established fact. RNA molecules have a short half-life (minutes to hours in cells) compared to DNA (years in some cells). Their instability means they are constantly being degraded and replaced. This rapid turnover, combined with the lack of a proofreading mechanism in RNA synthesis, leads to a much higher mutation rate — roughly 100 to 1000 times faster than DNA replication.
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Examine the Reason (R): “The presence of 2'–OH group in every nucleotide of RNA makes it labile and easily degradable.”
This is chemically accurate. In RNA, each ribose sugar has a hydroxyl group (–OH) attached to the 2' carbon. This –OH group is a nucleophile — it can attack the adjacent phosphodiester bond (specifically the phosphorus atom) in a reaction called intramolecular transesterification. This reaction breaks the RNA backbone, especially under alkaline conditions or in the presence of certain enzymes (RNases). DNA lacks this 2'–OH (it has just a hydrogen atom), so it is far more resistant to hydrolysis.
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Check if Reason (R) correctly explains Assertion (A):
The chemical lability caused by the 2'–OH group directly leads to the instability of RNA. Because RNA is easily broken down, it has a short lifespan. This rapid turnover means errors (mutations) introduced during transcription are not corrected and can accumulate quickly. Moreover, the same chemical reactivity makes RNA prone to spontaneous damage (e.g., deamination, depurination) at a higher rate than DNA. So, the reason directly explains why RNA is both unstable and mutates faster.
Watch outA common mistake is to think that the 2'–OH group only affects stability, not mutation rate. But remember: instability and high mutation rate are linked — a molecule that degrades quickly also has less opportunity for repair, so errors persist.
- Match with the given codes:
- Assertion (A) is true.
- Reason (R) is true.
- Reason (R) is the correct explanation of Assertion (A). This corresponds to option (A).
TipA quick way to remember: “RNA has an extra OH — that’s why it’s OH-so-unstable!” The 2'–OH is the chemical “handle” that makes RNA both fragile and error-prone.
✓Final answerThe correct option is (A) — both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
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- CBSE 2024Set BOTANY1 markMCQQ.Fill in the blank selecting the appropriate alternative: The position of additional OH group in ribose sugar of RNA is ____.(i) 2'(ii) 3'(iii) 4'(iv) 5'
›Reveal solutionSolution
The 2'-OH group on ribose is what distinguishes RNA sugar from DNA's deoxyribose.
Both DNA and RNA nucleotides contain a pentose sugar attached to a nitrogenous base and a phosphate group. In DNA, the sugar is deoxyribose, which has only a hydrogen atom at the 2' carbon (hence 'deoxy', i.e., oxygen removed at that position). In RNA, the sugar is ribose, which retains a hydroxyl (–OH) group at the 2' carbon in addition to the 3'-OH used for the phosphodiester backbone. This extra 2'-OH makes RNA chemically more reactive and less stable than DNA, and is one of the reasons DNA is favoured as the stable genetic material.
✓Final answer(i) 2'.
- CBSE 2024Set ANNUAL1 markMCQQ.At which position, in RNA, in every nucleotide residue an additional -OH group is present in the ribose?(a) 5' position(b) 3' position(c) 2' position(d) 4' position
›Reveal solutionSolution
The chemical difference between ribose (in RNA) and deoxyribose (in DNA) is a single -OH group at the 2' carbon of the sugar ring, present in RNA and absent (replaced by -H) in DNA.
Both DNA and RNA are built from a sugar-phosphate backbone, but their sugars differ: DNA uses 2'-deoxyribose (H at the 2' position), while RNA uses ribose, which retains a hydroxyl (-OH) group at the 2' position of every nucleotide. This extra -OH is what makes RNA chemically less stable than DNA and is one of the key structural distinctions between the two nucleic acids.
✓Final answer(c) 2' position.
- CBSE 2023Set ANNUAL1 markMCQQ.Which nitrogenous base is not present in a DNA molecule?(a) Adenine(b) Guanine(c) Cytosine(d) Uracil
›Reveal solutionSolution
DNA's four nitrogenous bases are adenine, guanine, cytosine and thymine; uracil is the base unique to RNA, where it takes the place of thymine.
DNA is built from two purines (adenine and guanine) and two pyrimidines (cytosine and thymine), with base pairing following A=T and G≡C. RNA, in contrast, uses uracil in place of thymine — U pairs with A wherever RNA base-pairs (e.g., during transcription or in tRNA folding). Thymine has an extra methyl group compared to uracil, which is thought to make DNA more chemically stable and better suited as the long-term genetic material.
✓Final answer(d) Uracil.
- CBSE 2021Set D1 markMCQQ.DNA is genetic material of(a) TMV(b) Bacteriophage(c) Both (A) and (B)(d) None of these
›Reveal solutionSolution
Of the options, DNA is the genetic material only in bacteriophage.
The Hershey–Chase experiment (1952) proved that DNA is the genetic material of bacteriophage (T2). In Tobacco Mosaic Virus (TMV), however, the genetic material is RNA, not DNA — as shown by Fraenkel-Conrat and Singer. Therefore, among the choices given, DNA is the genetic material only of the bacteriophage, so 'Both (A) and (B)' is incorrect.
✓Final answer(B) Bacteriophage.
- CBSE 2019Set ANNUAL1 markMCQQ.Uracil is present in(a) DNA(b) Protein(c) RNA(d) Sugar
›Reveal solutionSolution
Uracil is a nitrogenous base unique to RNA, replacing the thymine found in DNA.
Nucleic acids contain nitrogenous bases of two types: purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil).
- DNA contains the pyrimidines cytosine and thymine.
- RNA contains the pyrimidines cytosine and uracil in place of thymine.
Uracil pairs with adenine during transcription and translation, just as thymine would in DNA, but it lacks the methyl group that thymine has. Since RNA (option c) is the only nucleic acid among the choices that contains uracil, and protein (b) and sugar (d) are not nucleic acids at all, the answer is RNA.
✓Final answer(c) RNA.
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