(Transcribed from Dr. Cadilla’s lecture, 28 Mar 2000 by Brian Buschman)
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Mitochondrial DNA has less then 40 genes and resembles prokaryotic DNA. They are maternally inherited since it comes from the organelles that come from the oocyte.
The common eukaryotic genes are made up of exons and introns. Introns are extraneous bases sequences located between the translatable exons. Part of the post-translational processing of mRNA is the removal of introns. mRNA molecules also receive a 5’ cap and a 3’ poly A tail to prevent degradation.
The introns are removed by spliceosomes. The mRNA has a 5’ donor and 3’ acceptor splice site. Small nuclear RNAs (snRNA) U1, U2, U3, U4, U5 and U6 bind to the introns and form it into a loop that brings the donor and acceptor close together. The spliceosome then cuts the introns. The final step is ligation which is carried out by lariat.
In a given mRNA sometimes certain exons are removed with the introns. This makes it possible for an individual mRNA to be able to code for more then one protein. Different proteins that are made by removing different exons with the introns will make similar proteins yet they will be unique. This process is also able to produce many different mutations including additions, deletions, nonsense and frame shifts.
There are various types of gene families which are sets of genes with a commonality of some sort.
Duplicated genes are simply what they sound like, a duplicated gene. They often are duplicated because they code for the more commonly transcribed proteins.
Pseudogenes are unexpressed DNA sequences that are very similar to a normal gene but had a number of mutations that make it different.
Processed pseudogenes are similar to a normal gene but they were created by reverse transcription. Such a gene will not have introns but will also not have the promoter so it cannon be transcribed.
Repetitive sequences can be interspersed one here one there or as a tandem sequence meaning that multiple copies are back to back. The repetitive sequences can come as short interspersed elements (SINEs) or as long interspersed elements (LINEs). SINEs are a few hundred bases and LINEs are up to thousands of bases long. Both can usually be found in 1000-500,000 copies in the genome.
There are also sequences called microsatellites and minisatellites that are tandem repeats useful in tracing gene inheritance. This information is useful in criminal and paternity cases. Microsatellites are only 2-4 bases and minisatellites are longer but less then 1000 bases.
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