Biological Importance of Nucleic Acids

The familiar form of the nucleic acid makes life possible.

Nucleic acids carry genetic information within their structure. All living things have some form of nucleic acids, which allow for the translation of proteins in order to carry out important functions of the cell.

Structure

Nucleic acids are large macromolecules composed of smaller nucleotides. These nucleotides are made up of two backbones that alternate between sugar groups and phosphate molecules (the phosphate makes it slightly acidic). Extending from both sides of these sugar groups are two nucleotide bases that bond to each other. These bonding patterns give rise to the double helix shape that we are familiar with.

DNA

Deoxyribonucleic acid is the most common form. Its base pairs are adenine (A), thymine (T), guanine (G) and cytosine (C). There are small differences between them. For instance, A and G have a double ring structure, which allows them to bind to a single ring structure. A binds with T, and G binds with C. When DNA is replicated, its structure unwinds, splitting the hydrogen bonds of the bases in half. Complimentary bases are then formed. This is similar in concept to the way in which DNA is read.

RNA

Another kind of nucleic acid is ribonucleic acid, which is similar in structure to DNA but instead supplements uracil (U) for thymine. RNA is used exclusively in viruses and perhaps even the earliest forms of life, but in most modern life RNA has another critical function. It translates genetic information to proteins, which help facilitate important functions of the cell.

Transcription

When a protein needs to be made, it begins with transcription. The first step occurs when an enzyme called RNA polymerase binds to what is known as a promoter in the DNA. When the DNA unwinds, the RNA polymerase then reads along the DNA and creates a single strand of RNA. Reading G will create C on the RNA and vice versa. T will also create A, but A will create U. In the end, it works just as well. RNA polymerase is controlled by start and stop codes in the DNA. When it is finished, RNA polymerase modifies the RNA strand to create a unique sequence with caps on them.

Translation

The new strand of RNA, now called messenger RNA, binds to a complex called a ribosome. Another type of RNA, called transfer RNA, then attempts to match up with every three nucleotide bases (a codon) of the mRNA. For instance, a codon of AUG will match up with UAC on the tRNA. Every tRNA is carrying a specific amino acid. There are 64 codons but only 20 amino acids, so some code for multiple amino acids. When the amino acids are lined up using the RNA code, they form a protein, which is shipped off to another part of the cell to do its function. Some proteins can be hundreds of amino acids long.

Other Types

DNA and RNA are not the only types of nucleic acids. Peptide nucleic acid, which exists artificially, has a simpler pseudo-peptide backbone and bases of purine and pyrimidine. There are other kinds of acids, such as glycol nucleic acid and threose nucleic acid. It has been hypothesized that one of these could have been a precursor to RNA in the first forms of life, but the evidence is not strong.

References

• Vision Learning: Nucleic Acids
• John Kyrk Animation: DNA Makes RNA
• John Kyrk Animation: RNA Makes Protein
• Horizon Press: PNA Peptide Nucleic Acid