Q.Genes are made up of _____.
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🔒 Start your 14-day free trial to unlock the full solution →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 t …
The chemical identity of the gene was settled by a chain of classic experiments — Griffith's transformation, Avery-MacLeod-McCarty's enzyme digestion tests, and the Hershey-Chase phage experiment — which together showed that hereditary information is carried by a specific nucleic acid, …
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 …
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 …
- 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 stor …
- 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 …
- 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 hydr …
- 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 accura …
- 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 i …
- 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): …
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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 p …
- 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 nucle …
- 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). …
- 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 ch …
- 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. …
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