Difference Between Cytosine and Thymine

Cytosine vs Thymine
 

Nucleotide is a building block of nucleic acids such as DNA and RNA. It is composed of three main components: pentose sugar, a nitrogenous base and phosphate groups. There are five different nitrogenous bases present in nucleic acids. They are adenine, guanine, thymine, uracil, and cytosine. Adenine and guanine are purines. Thymine, uracil and cytosine are pyrimidines which have one heterocyclic aromatic ring structure. The key difference between cytosine and thymine is that cytosine is a pyrimidine base found in both DNA and RNA and pairs with guanine by three hydrogen bonds while thymine is a pyrimidine base found only in DNA and pairs with adenine by two hydrogen bonds.

CONTENTS
1. Overview and Key Difference
2. What is Cytosine
3. What is Thymine
4. Side by Side Comparison – Cytosine vs Thymine
5. Summary

What is Cytosine?

Cytosine is one of the nitrogenous bases found in DNA and RNA. It is a pyrimidine derivative which has one heterocyclic aromatic carbon ring structure. The molecular formula of cytosine is C₄H₅N₃O. The complementary base of the cytosine is guanine, and it forms three hydrogen bonds to pair with guanine during the complementary base pairing in the DNA helix. Cytosine has two groups attached to its heterocyclic ring. At C4 position, there is an amine group, and at C2 position there is a keto group, as shown in the figure.

Cytosine carries genetic information of organisms. It is present both in DNA and RNA and participates in the genetic code of the genes. Cytosine also plays different other roles in the cells. It acts as an energy carrier and cofactor cytidine triphosphate (CTP).

What is Thymine?

Thymine is one of the nitrogenous bases found in DNA. It is a pyrimidine derivative which has one heterocyclic aromatic carbon ring in its structure. The chemical formula of thymine is C₅H₆N₂O₂. In RNA, thymine is replaced with uracil. Thymine binds with adenine by forming two hydrogen bonds during the complementary base pairing. Thymine has two keto groups at C2 and C4 positions and CH₃ group at C5 position in its heterocyclic aromatic ring as shown in figure 02.

Thymine is a part of genetic codes of organisms. However, thymine dimers are the commonest mutations that occur in DNA upon exposure to ultraviolet radiation. It occurs when two thymine bases are adjacent to each other in the backbone of DNA.

Thymine can form a derivative called thymidine triphosphate (TTP) which is an important intermediate in the transfer of chemical energy in living cells.

What is the difference between Cytosine and Thymine?

Summary – Cytosine vs Thymine

Cytosine and thymine are two important nitrogenous bases found in nucleic acids of organisms. They are involved in carrying genetic information and in other functions of the cells. Both bases have a heterocyclic carbon ring in their structures, which categorize them into pyrimidine group. Cytosine is present in both DNA and RNA while thymine is present only in DNA. Cytosine binds with guanine and thymine binds with adenine by hydrogen bonds to stabilize DNA double helix. Cytosine makes three hydrogen bonds with guanine and thymine makes two hydrogen bonds with adenine during the base pairing. This is the difference between cytosine and thymine.

Reference:
1.Marlaire, Ruth. “NASA Ames Reproduces the Building Blocks of Life in Laboratory.” NASA. NASA, 03 Mar. 2015. Web. 25 Apr. 2017
2.”Nucleic acid structure.” ATDBio. N.p., n.d. Web. 25 Apr. 2017
3.”Cytosine.” Cytosine – New World Encyclopedia. N.p., n.d. Web. 25 Apr. 2017

Image Courtesy:
1.”Cytosine chemical structure” By Engineer gena – Own work (Public Domain) via Commons Wikimedia
2.”Thymine skeletal” By Daveryan at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia