Pyrimidines are nitrogenous bases with 1 ring structure, whereas purines are nitrogenous bases with 2 ring structures. Cytosine and thymine are pyrimidines since they both have one ring structure, whereas adenine and guanine are purines with two connected ring structures.

Cytosine, thymine, and uracil are classified as pyrimidines which have a single carbon-nitrogen ring as their primary structure (Figure 1). Each of these basic carbon-nitrogen rings has different functional groups attached to it.

Purines. -A clam of organic molecules each having a double ring of carbon and nitrogen atoms.

The pyrimidines (cytosine, uracil, and thymine) only have one single ring, which has just six members and two nitrogen atoms.

Because of their structural similarity, we usually refer the nine-member double rings adenine and guanine as purines, and six-member single-ring thymine, uracil, and cytosine are pyrimidines. Fig. 1.5. (A) Chemical structure of pyrimidines and purines nitrogenous bases in DNA and RNA.

Nitrogenous base: A molecule that contains nitrogen and has the chemical properties of a base. The nitrogenous bases in DNA are adenine (A), guanine (G), thymine (T), and cytosine (C). The nitrogenous bases in RNA are the same, with one exception: adenine (A), guanine (G), uracil (U), and cytosine (C).

The basic property derives from the lone electron pair on the nitrogen atom. The nitrogen bases are also called nucleobases because they play a major role as building blocks of the nucleic acids deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

There are four different DNA nucleotides, each defined by a specific nitrogenous base: adenine (often abbreviated “A” in science writing), thymine (abbreviated “T”), guanine (abbreviated “G”), and cytosine (abbreviated “C”) (Figure 2).

RNA consists of four nitrogenous bases: adenine, cytosine, uracil, and guanine.

DNA is made of chemical building blocks called nucleotides. These building blocks are made of three parts: a phosphate group, a sugar group and one of four types of nitrogen bases. To form a strand of DNA, nucleotides are linked into chains, with the phosphate and sugar groups alternating.

Components of DNA DNA is a polymer. The monomer units of DNA are nucleotides, and the polymer is known as a “polynucleotide.” Each nucleotide consists of a 5-carbon sugar (deoxyribose), a nitrogen containing base attached to the sugar, and a phosphate group.

The sugar is deoxyribose in DNA and ribose in RNA. The purines have a double ring structure with a six-membered ring fused to a five-membered ring. Pyrimidines are smaller in size; they have a single six-membered ring structure. The sugar is deoxyribose in DNA and ribose in RNA.

Ribose is a single-ring pentose [5-Carbon] sugar. The numbering of the carbon atoms runs clockwise, following organic chemistry rules.

Pentose sugars – 5-Carbon sugar 1) Deoxyribose – in DNA 2) Ribose – in RNA b.

Glucose is a monosaccharide containing six carbon atoms and an aldehyde group, and is therefore an aldohexose. The glucose molecule can exist in an open-chain (acyclic) as well as ring (cyclic) form….Glucose.

Two types of pentose are found in nucleotides, deoxyribose (found in DNA) and ribose (found in RNA).

The five-carbon sugar in DNA is called deoxyribose, while in RNA, the sugar is ribose. These two are very similar in structure, with just one difference: the second carbon of ribose bears a hydroxyl group, while the equivalent carbon of deoxyribose has a hydrogen instead.

The sugar found in RNA is ribose, whereas the sugar found in DNA is deoxyribose, both of which are 5-carbon sugars.

During evolution ribose was selected as the exclusive sugar component of nucleic acids. The selection is ex- plained by using molecular models and by eliminating most of the other common sugars by looking at their chemical structure and envisioning how they would fit in a nucleic acid model.

uracil

In RNA, the base thymine is not found and is instead replaced by a different base called uracil, abbreviated U. The other three bases are present in both DNA and RNA.

RNA is single stranded while DNA is double stranded. – RNA contains the deoxyribose sugar while DNA contains the deoxyribose sugar which means that DNA lacks one Oxygen containing hydroxyl group. As RNA is single stranded its nitrogenous bases are not away from the water, that makes it more reactive than that of DNA.

1) RNA has 2′-OH group on the pentose ring which makes it very reactive and it is more susceptible to hydrolysis. 2) RNA has the nitrogenous base Uracil compared to Thymine in DNA. Uracil is more reactive than thymine.