Introduction to Nucleic Acids

If you are unfamiliar with nucleic acids, this page should supply you with enough background information to make searching the various databases more meaningful.

The links below will connect you to diagrams and glossary entries that will help you understand the text or provide more information about a specific subject.

What is deoxyribonucleic acid, or DNA?

All living things contain DNA. DNA is a large molecule that encodes the "blueprints" for an organism's development and growth.

The basic unit of DNA is called a nucleotide, which is in turn composed of a sugar, a phosphate, and a nitrogen-containing base. Four different types of bases are found in DNA: A (adenosine), C (cytidine), G (guanosine), and T (thymidine). The structure of these nitrogen bases differentiate nucleotides from each other.

To make DNA, these nucleotide monomers are joined together in a linear fashion, forming a long chain like beads in a necklace. A DNA molecule consists of two of these long polymers (beaded necklaces) twisted into a helix. The two strands of a DNA molecule are held together by hydrogen bonds between bases on opposite strands; A is able to pair with T, and C is able to pair with G. DNA resembles a spiraling staircase; the bases are analogous to the steps, while the sugar and phosphate groups are the handrails and banisters. To view a picture of the "staircase", click here. The linear order of bases along a DNA strand is called the "DNA sequence."

How does the DNA code work?

Just as Morse code represents all of the letters of the alphabet with dots and dashes, DNA represents all of the building blocks of proteins (amino acids) with different triplet combinations of the bases A, C, G , and T along a DNA strand. Although DNA consists of two intertwined strands, generally only one of the two strands codes for a specific protein. Much of the housing and molecular machinery inside a cell are composed at least in part of proteins, so DNA holds the "blueprint" for all cellular structures. A length of DNA sequence that codes for an entire protein is called a gene.

Is DNA the only nucleic acid molecule?

No, there is another type of nucleic acid called ribonucleic acid, or RNA. RNA, like DNA, is made of nucleotides. The sugar of RNA is slightly different than the one found in DNA; this difference accounts for the names of the two molecules (deoxyribose versus ribose). One of the bases in DNA, thymidine, is substituted by a different base, uridine (U) in RNA. Unlike the large double-stranded DNA, RNA molecules have only one strand and are generally smaller. RNA can be thought of as an intermediate in the decoding of DNA into protein; genes in DNA are copied into an RNA molecule through a process called transcription and the RNA is then decoded (translated) into amino acids that make a protein.

Why does anyone care about the gene sequences contained in DNA?

By studying the DNA sequences and comparing one organism's genes with another, scientists hope to understand how cells function and what is necessary to make a living organism. Gene sequences can also be used to figure out the evolutionary relationships between organisms.

Further Reference

Nucleic acid nomenclature

See a list of Nucleic Acid Sequence Databases and
examples for searching Nucleic Acid Sequence Databases.

Last updated: July 23, 1998
URL: http://biotech.icmb.utexas.edu/pages/science/nucacid_intro.html
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