Difference Between Thymine and Uracil

Thymine and Uracil are the two nucleotide bases which are found in the DNA and RNA respectively. The main difference between thymine and uracil is due to the property of “Occurrence”.

The occurrence of both thymine and uracil is the property that distinguishes these two, as thymine is a pyrimidine nitrogenous base found in Deoxyribonucleic acid (DNA) whereas Uracil is a pyrimidine nitrogenous base found in Ribonucleic acid (RNA).

In Deoxyribonucleic acid, the pyrimidine bases are cytosine and thymine, and in Ribonucleic acid, the pyrimidine bases are cytosine and uracil.

Content: Thymine Vs Uracil

  1. Comparison Chart
  2. Definition
  3. Difference in structure
  4. Difference in Functions
  5. Similarities between Thymine and Uracil
  6. Key Differences Between Thymine and Uracil
  7. Conclusion

Comparison Chart

PropertiesThymineUracil
UracilIt is the pyrimidine base of the DNAIt is the pyrimidine base of the RNA
OccurrenceFound only in DNAFound only in RNA
Presence of keto groupTwo keto groups present at C-2 and C-4 atom Two keto groups present at C-2 and C-4 atom
Presence of methyl groupOne methyl group present at C-5 atomNot present
Molecular formulaC5H6N2O2C4H4N2O2
Molar mass126.1133 g/mol112.0868 g/mol

Definition

Thymine: It is the nitrogenous base which comes under the type of pyrimidine base which appears as single ring structure that is found in the backbone of deoxyribonucleic acid where it complementary pairs with the purine base, i.e. Adenine by two hydrogen bonds.

Uracil: It is the nitrogenous base which comes under the type of pyrimidine base which appears as single ring structure that is found in the backbone of ribonucleic acid where it complementary pairs with the purine base, i.e. Adenine by two hydrogen bonds.

Difference in structure

The difference in structure is due to their difference in the presence of functional groups like keto and methyl groups in their molecular structure.

Structure of thymine

Thymine is the pyrimidine base of the DNA which contains two keto groups at C-2 and C-4 position and also one methyl group at the C-5 position. It is denoted as T.

thymine structure

It is synthesized by uracil by the process of methylation, where uracil is methylated at the C-5 position of the pyrimidine ring and due to this fact thymine also refers as “5-Methyl uracil”. In DNA helix, the complementary pair of thymine is the purine base that is “Adenine”. Therefore, T and A pairs with each other by the formation of two hydrogen bonds.

Structure of Uracil

Uracil is the pyrimidine base of the DNA which contains two keto groups at C-2 and C-4 position. It is denoted as U.

uracil structure

In an RNA molecule, the complementary pair of uracil is the purine base that is “Adenine”. Therefore, U and A pairs with each other by the formation of two hydrogen bonds.

Important facts

As we know, both thymine and uracil are the nitrogenous bases but when the nitrogenous base combines with pentose sugar then it forms “Nucleoside”. When nitrogenous base combines with both pentose sugar and one to three phosphate group then it forms “Nucleotide”.

Therefore when thymine combines with DNA pentose sugar, then it will form “Deoxythymidine”. Same goes with the case of uracil, i.e. it will form “Uridine” by combining with RNA pentose sugar.

Now coming onto the concept of nucleotide, when T ( thymine) combines with DNA pentose sugar and monophosphate group then it will form “Deoxythymidine-5’ monophosphate” (5’-dTMP). If T combines with diphosphate in place of monophosphate then it will form “Deoxythymidine-5’ diphosphate” (5’-dTDP). And, if T combines with triphosphate rather than mono and di-phosphate, then it will form “Deoxythymidine-5’triphosphate” (5’-dTTP).

Uracil when combining with RNA pentose sugar and monophosphate group then it will form “Uridine-5’monophosphate” (5’-dUMP). If U combines with diphosphate in place of monophosphate then it will form “Uridine -5’ diphosphate” (5’-dUDP). And, if U combines with triphosphate rather than mono and di-phosphate, then it will form “Uridine -5’triphosphate” (5’-dUTP).

Similarities between Thymine and Uracil

  • Both thymine and uracil are the nitrogenous bases which are present in the nucleic acid, i.e. DNA and RNA.
  • Thymine and uracil are the two pyrimidine nitrogenous bases.
  • Both complementary pairs with the purine base i.e.“Adenine”.
  • Both can form a dimer in the presence of ultraviolet light.

Key Differences Between Thymine and Uracil

  1. Thymine is the pyrimidine base of the DNA, whereas Uracil is the pyrimidine base of the RNA.
  2. The occurrence of thymine and uracil is a crucial difference as thymine is only found in DNA and uracil is only found in RNA.
  3. Methyl group is absent in uracil whereas present in thymine at the C-5 position.
  4. The molecular formula of thymine is C5H6N2O2, whereas the molecular formula of uracil is C4H4N2O2.
  5. Thymine has a molar mass of 126.1133 g/mol and uracil has a molar mass of 112.0868 g/mol.

Conclusion

Therefore, we can conclude that thymine and uracil are the two pyrimidine nitrogenous bases which are having the different molecular structure (due to the presence of methyl group in thymine), different molecular formula, molecular weight and difference in their occurrence. Instead of many differences, there are similarities also like the type of nitrogenous base, their complementary base pair etc.

So, we can say thymine and uracil are the part of genetic material, i.e. DNA and RNA, respectively, where these two bases occur in the structure and backbone of both DNA and RNA.

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