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The Radio-Edit Definition

A nucleic acid is a large molecule composed of nucleotide subunits. A nucleotide consists of a nitrogenous base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule.


The DNA Dance Mix

What is DNA?

All living things contain deoxyribonucleic acid, or 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 (adenine), C (cytosine), G (guanine), and T (thymine). 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 spiral staircase; the bases are analogous to the steps, while the sugar and phosphate groups are the handrails and banisters. 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 and to treat many diseases. Gene sequences can also be used to figure out the evolutionary relationships between organisms.

From the BioTech Project at http://biotech.icmb.utexas.edu/. Written mostly by Brent Shelley with a few additions by myself. Used with permission. For further information see the BioTech homenode.

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