DNA vs RNA
DNA and RNA are nucleic acids. Both are polymers of nucleotides, and each nucleotide contains a pentose sugar, nitrogenous base and phosphate group.
RNA → Ribonucleic Acid
The most important differences asked in examinations are the type of pentose sugar and the nitrogenous bases.
DNA
DNA contains the pentose sugar 2-deoxyribose.
At the 2′ carbon, DNA sugar has hydrogen (H) instead of a hydroxyl (OH) group.
RNA
RNA contains the pentose sugar ribose.
At the 2′ carbon, RNA sugar contains a hydroxyl (OH) group.
RNA → Ribose
DNA Bases
DNA contains four nitrogenous bases:
Thymine (T)
Guanine (G)
Cytosine (C)
RNA Bases
RNA also contains four nitrogenous bases, but Uracil replaces Thymine.
Uracil (U)
Guanine (G)
Cytosine (C)
The major difference between DNA and RNA nitrogenous bases is that DNA contains thymine whereas RNA contains uracil.
RNA → Uracil (U)
Adenine, guanine and cytosine are common to both DNA and RNA.
Different base: DNA = T | RNA = U
| Property | DNA | RNA |
|---|---|---|
| Full form | Deoxyribonucleic Acid | Ribonucleic Acid |
| Pentose sugar | 2-Deoxyribose | Ribose |
| Sugar at 2′ carbon | H | OH |
| Purine bases | Adenine, Guanine | Adenine, Guanine |
| Pyrimidine bases | Cytosine, Thymine | Cytosine, Uracil |
| Unique base | Thymine (T) | Uracil (U) |
| Common bases | A, G, C | A, G, C |
Purines
Purines are double-ring nitrogenous bases.
Guanine (G)
Pyrimidines
Pyrimidines are single-ring nitrogenous bases.
Thymine (T) → DNA
Uracil (U) → RNA
Pyrimidines → C + T + U
DNA
G pairs with C
RNA
G pairs with C
RNA → A–U
RNA uses uracil as its pyrimidine base, whereas DNA uses thymine.
Chemically, thymine is essentially 5-methyluracil. The methyl group helps distinguish normal thymine in DNA from cytosine-derived modifications and contributes to DNA's long-term information-storage role.
RNA → Uracil
Q. Differentiate between DNA and RNA on the basis of their pentose sugar and nitrogenous bases.
Answer:
| DNA | RNA |
|---|---|
| Contains 2-deoxyribose sugar. | Contains ribose sugar. |
| Contains A, T, G and C. | Contains A, U, G and C. |
Q. Give three differences between DNA and RNA with respect to sugar and nitrogenous bases.
Answer:
- DNA contains 2-deoxyribose, whereas RNA contains ribose.
- DNA contains thymine, whereas RNA contains uracil.
- Adenine, guanine and cytosine are common nitrogenous bases in both DNA and RNA.
Q. Compare DNA and RNA on the basis of pentose sugar and nitrogenous bases. Also mention their base-pairing rule.
Answer:
| Basis | DNA | RNA |
|---|---|---|
| Sugar | 2-Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Pairing | A–T and G–C | A–U and G–C |
Q. Explain the differences between DNA and RNA with reference to their sugar and nitrogenous bases.
1. Pentose Sugar
DNA contains 2-deoxyribose, while RNA contains ribose.
RNA → Ribose
2. Nitrogenous Bases
DNA contains adenine, thymine, guanine and cytosine. RNA contains adenine, uracil, guanine and cytosine.
RNA → A, U, G, C
3. Major Difference
Thymine is present in DNA, whereas uracil is present in RNA.
4. Base Pairing
RNA: A–U, G–C
RNA → Ribose + Uracil
Q. Differentiate between DNA and RNA in detail on the basis of pentose sugar, nitrogenous bases and base pairing.
1. Pentose Sugar
DNA contains 2-deoxyribose. It lacks the OH group at the 2′ carbon and has H at that position.
RNA contains ribose, which has an OH group at the 2′ carbon.
RNA: 2′ carbon → OH
2. Nitrogenous Bases
Both DNA and RNA contain the purines adenine and guanine, and the pyrimidine cytosine.
The fourth base differs:
RNA → Uracil
3. Base Pairing
A–T
G–C
RNA:
A–U
G–C
4. Final Comparison
| Feature | DNA | RNA |
|---|---|---|
| Sugar | 2-Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Unique pyrimidine | Thymine | Uracil |
RNA = Ribose + Uracil
1. The sugar present in DNA is:
✅ Answer
C) 2-Deoxyribose
2. The sugar present in RNA is:
✅ Answer
A) Ribose
3. Which sugar has H instead of OH at the 2′ carbon?
✅ Answer
B) 2-Deoxyribose
4. Which nitrogenous base is present in DNA but not normally in RNA?
✅ Answer
C) Thymine
5. Which base replaces thymine in RNA?
✅ Answer
B) Uracil
6. Which bases are common to both DNA and RNA?
✅ Answer
A) A, G, C
7. The pyrimidine base unique to DNA is:
✅ Answer
B) Thymine
8. The pyrimidine base unique to RNA is:
✅ Answer
B) Uracil
9. Which of the following are purines?
✅ Answer
A) A and G
10. Which is a pyrimidine?
✅ Answer
C) Cytosine
11. In DNA, adenine pairs with:
✅ Answer
B) Thymine
12. In RNA, adenine pairs with:
✅ Answer
B) Uracil
13. Guanine pairs with:
✅ Answer
C) Cytosine
14. Which statement is correct?
✅ Answer
C) DNA contains deoxyribose
15. RNA contains which base instead of thymine?
✅ Answer
C) Uracil
16. The 2′ carbon of ribose in RNA contains:
✅ Answer
B) OH
17. The 2′ carbon of deoxyribose contains:
✅ Answer
B) H
18. Which pair is correctly matched?
✅ Answer
C) DNA – Thymine
19. Which pair is correctly matched?
✅ Answer
B) RNA – Uracil
20. The most important difference in nitrogenous bases between DNA and RNA is:
✅ Answer
C) T in DNA is replaced by U in RNA
🎯 Quick Revision
RNA: Ribonucleic Acid
DNA Sugar: 2-Deoxyribose
RNA Sugar: Ribose
DNA Bases: A, T, G, C
RNA Bases: A, U, G, C
DNA Unique Base: Thymine (T)
RNA Unique Base: Uracil (U)
DNA Pairing: A–T, G–C
RNA Pairing: A–U, G–C
Golden Rule: DNA = Deoxyribose + Thymine
RNA = Ribose + Uracil
