Difference Between Thymine and Thymidine

The key difference between thymine and thymidine is that thymine is a nucleobase, whereas thymidine is a nucleoside.

The term thymine and thymidine occur in biochemistry and organic chemistry as structures related to nucleic acids. Nucleic acid such as DNA and RNA are composed of nucleotides. A nucleotide contains a nucleobase, sugar molecule and a phosphate group. The combination of a nucleobase with a sugar forms a nucleoside.

CONTENTS

1. Overview and Key Difference
2. What is Thymine 
3. What is Thymidine
4. Side by Side Comparison – Thymine vs Thymidine in Tabular Form
5. Summary

What is Thymine?

Thymine is a type of nucleobase having the chemical formula C₅H₆N₂O₂. It is an organic compound having the molar mass 126.15 g/mol. It is one of the four major nucleobases in nucleic acids of DNA. The other three nucleobases are guanine, cytosine and adenine. This nucleobase falls under the category of pyrimidine. This nucleobase is absent in RNA; it has uracil instead of thymine.

When considering the properties of thymine, it pairs with adenine in DNA structures. Thymine is derived from the methylation of uracil at 5^th carbon; therefore, it is called 5-methyluracil. Thymine can bind with adenine via a double bond. This double bond is a pair of hydrogen bonds. These two hydrogen bonds are helpful in stabilizing the DNA structure and nucleobase structure as well.

Formation of thymine dimers is a common type of mutation in DNA. Here, a pair of adjacent thymine or cytosine forms thymine dimers (formation of bonds between consecutive nucleobases) that cause the formation of kinks that can inhibit the normal function of DNA. Apart from that, thymine bases can be oxidized to form hydantoins. This occurs after the death of an organism.

What is Thymidine?

Thymidine is a type of pyrimidine deoxynucleoside having the chemical formula C₁₀H₁₄N₂O₅. The molar mass of this organic compound is 242.23 g/mol. It is a nucleoside formed from the combination of thymine and deoxyribose sugar. This nucleoside can be phosphorylated to form nucleotides. Here, it may undergo phosphorylation with one phosphate group (this forms deoxythymidine monophosphate), with two phosphate groups (forming deoxythymidine diphosphate) or with three phosphate groups (forming three phosphate groups).

Thymidine can exist in vitro conditions as a solid (as white crystals or as white crystalline powder). Under standard temperature and pressure, the stability of this compound is very high. As a part of DNA structure, thymidine occurs in living organisms (also in DNA viruses). Therefore, it is a non-toxic compound. In RNA, there is uridine instead of thymidine. Uridine is formed from the combination of uracil with ribose sugar.

What is the Difference Between Thymine and Thymidine?

The key difference between thymine and thymidine is that thymine is a nucleobase, whereas thymidine is a nucleoside. Besides, thymine is a type of nucleobase having the chemical formula C₅H₆N₂O₂ while thymidine is a type of pyrimidine deoxynucleoside having the chemical formula C₁₀H₁₄N₂O₅.

Moreover, thymine is a single planar molecule while thymidine is a combination of two molecules; ribose sugar and thymine.

The following table summarizes the difference between thymine and thymidine.

Summary – Thymine vs Thymidine

The term thymine and thymidine come in biochemistry and organic chemistry as structures related to nucleic acids. The key difference between thymine and thymidine is that thymine is a nucleobase, whereas thymidine is a nucleoside.

Reference:

1. “Thymine.” Wikipedia, Wikimedia Foundation, 24 Apr. 2020, Available here.
2. “Thymidine.” Thymidine – an Overview | ScienceDirect Topics, Available here.
3. Thymidine.” Wikipedia, Wikimedia Foundation, 16 May 2019, Available here.

Image Courtesy:

1. “Thymine skeletal” By Daveryan at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Desoxythymidin” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia