A Beginner's Guide to Nucleic Acids

Nucleic acids such as DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) provide organisms with a means for storing and transmitting genetic information. These linear, unbranched biopolymers are made up of building blocks called nucleotides. To begin our examination of nucleic acids, let's first take a closer look at nucleotides.

About Nucleotides

Nucleotides are the building blocks that, when combined, form nucleic acids. There are three components that make up a nucleotide:

• A five-carbon sugar (also called a 'pentose'). There are two types of pentoses, deoxyribose and ribose.
• A nitrogen-containing ring compound (also called a 'base'). There are two classes of base, purines (which include the bases adenine and guanine) and pyrimidines (which include the bases thymine, cytosine, and uracil).
• One, two or three phosphate groups.

The Five Bases

As noted above, each nucleotide contains a base. There are two classes of bases (purines and pyrimidines) which encompass a total of five bases:

• adenine - a purine that occurs in both DNA and RNA, it forms a base pair with thymine in DNA and with uracil in RNA.
• guanine - a purine that occurs in both DNA and RNA, it forms a base pair with cytosine.
• thymine - a pyrimidine that occurs only in DNA, it forms a base pair with adenine and in RNA it is replaced by uracil.
• cytosine - a pyrimidine that occurs in both DNA and RNA, it forms a base pair with guanine.
• uracil - a pyrimidine that occurs only in RNA, it forms a base pair with adenine and in DNA it is replaced by thymine.