How Does Nature Protect Our Genetic Code?

What Is The Genetic Code?

The genetic code has three important characteristics.

1. The genetic code is redundant. This means that more than one codon can code for the same amino acid. There are only three coons that do not code for any amino acid. These codons serve as “stop” signals to end protein synthesis.
2. The genetic code is continuous. This means that it reads as a series of three-letter codons without spaces, punctuation, or overlap. Therefore, knowing exactly where to start and stop protein synthesis is essential. A shift of one or two nucleotides in either direction can alter the codon groupings and result in an incorrect amino acid sequence. (1)
3. The genetic code is nearly universal. The universality of the genetic code means that a codon in the fruit fly codes for the same amino acid as in a human. This has important implications for genetic techniques, such as cloning. A gene that is taken from one kind of organism and inserted into another organism will produce the same protein. (1)

Cells utilize numerous repair processes to safeguard their DNA from damage.

1. As DNA replication proceeds, the replication complex through which DNA is threaded simultaneously builds a new strand of DNA and proofreads the work. Proofreading involves many of the enzymes of the replication complex, but DNA polymerase III plays perhaps the most important role. When DNA polymerase III inserts an incorrect nucleotide in a growing strand of DNA, it usually recognizes their mistake immediately, removes the nucleotide, and replaces it with the correct nucleotide. This proofreading mechanism alone greatly reduces to error rate of DNA replication. (2)
2. After DNA replication is completed, a second mechanism similar to the proofreading mechanism scans the new strand of DNA for errors missed by proofreading. When errors are found, incorrect nucleotides are removed and replaced by DNA polymerase III. This mechanism is called mismatch repair. (2)
3. During the life of a cell, there is always the potential for damage to the cell’s DNA, which in turn could result in the production of non-functional proteins. The DNA may be exposed to different mutagens which can chemically alter nucleotides, for example ultraviolet light. To guard against this type of damage, specialized enzymes continuously scan the cell’s DNA for any damage such as mismatched base pairs or even extra nucleotides. When damage is encountered, short stretches of DNA may be removed. These stretches are then replaced with the proper nucleotides through the activity of DNA polymerase and DNA ligase. This type of repair is called excision repair. (2)

References

1. The genetic code. (2010, April 22). Retrieved from http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Codons.html
2. Dna proofreading and repair. (n.d.). Retrieved from http://www.sci.uidaho.edu/bionet/biol115/t6_cell_growth/PDF/T6L2M2_DNA_proofreading_and_repair_transcript.pdf