Monday, March 30, 2009
Common ancestor
In chapter 3, Sean Carroll talks about Immortal genes that can be found in various organsims from different Kingdoms. What are some of examples of Immortal genes? Why are they so important that it never changes? From these immortal genes from different organsims, what can we conclude about LUCA( last universal common ancestor)?
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An immortal gene or an organism that does not age is called biologically immortal. Immortal genes are not limited by the Hayflick limit because the cells don't divide due to damage and shortened telomeres. Telomeres are caps at the end of the DNA strand and every time the DNA cell divides, the telomere becomes shorter and shorter causing aging. Some examples of immortal species are bacteria, Hydra, jellyfish, and Bristlecone Pines. Bacteria are considered immortal species because the cell divides and then the sister cell divides and then a colony is created which is essentially immortal. Hydra don't undergo aging, so therefore are considered to be immortal. Jellyfish transform back into the child or polyp stage so it therefore has an indefinite lifespan.
ReplyDeleteA stem cell that is immortal has been found called ESCs. ESCs can differentiate into many different cell types, and they can treat damaged cells or organs. The ESCs is called the "master gene" that can multiply forever while still being able to form into any type of cell. This cell type is called Nanog and makes ESCs immortal.
Also, the gene called MORF4 is considered an immortal gene because it makes a transcription factor that controls the activity of the gene.
Immortal genes are so important that they never change because they stop aging and the evolution of certain cells in the body of organisms. If those genes did start loosing their telomeres then they would no longer be immortal genes and would die off therefore creating a mutation in the DNA. If these genes are altered, then replication of these genes becomes jeopardized and when interacted with DNA, a mutation can occur. Also, immortal genes are vital for almost every life process in the human body.
The last universal common ancestor is the most recent organism from which all organisms today have descended from. Therefore, the genetic code from the LUCA is made up of all of the immortal genes that have been discovered. These immortal genes have lasted and have come from the first ancestor. Immortal genes are the only genes in the human DNA code today that have been passed down directly from the last universal common ancestor.
http://knol.google.com/k/eli-vieira-araujo-jnior/aging-and-immortality-in-biology/383nbl0kmwsgz/2#
http://www.newscientist.com/article/dn3786-stem-cell-immortality-gene-found.html
http://en.wikipedia.org/wiki/Immortality#Biological_immortality
http://www.sciencemag.org/cgi/content/summary/279/5348/177
http://en.wikipedia.org/wiki/Last_universal_ancestor
Jackie made many good points. I would like to add a few general thoughts to this question. As Carroll said, “More thought and attention has been directed to the ‘creative’ dimension of natural selection and how new traits evolve” (Carroll 72). Immortal genes serve to provide us with the preservative force of natural selection. Darwin called it getting rid of “injurious change”. This facet of evolution is often understated. So many biologists pay attention to the beneficial mutations; it is important to look at the mutations that go away as well. Immortal genes have another function to us: they give us clues about LUCA. All this will be explained in the following paragraphs.
ReplyDeleteOne important thing to remember is the redundancy of the genetic code. The sequence of bases can change without the final result (protein) changing. This occurs because more than one codon can code for each protein. An immortal gene might have a different base sequence in different organisms, but the final protein is the same. This feature of the genetic code is used to insulate DNA against injurious change. If a change in base sequence doesn’t change the protein being created, then there is no mutation, and there is no need for natural selection to kick in. This can save the organism from harm, because there is a good chance that if there was a mutation, the mutation would be harmful. Immortal genes remind us of the redundancy in the genetic code.
Immortal genes are not invulnerable to mutation; they mutate just like any other gene. Unlike other genes though, they stay intact as a unit for eternity, because they are essential. There is no mutation that could occur to them to improve them; they are perfect the way they are. Immortal genes have been mutated over and over again, and natural selection has time and time again reversed the mutations. Why is this important? It showcases the preservative side of natural selection instead of the creative side. The fact that there are genes that stay unchanged through millions of generations shows that natural selection works not only to improve but to preserve what already works.
As for LUCA, it shows that there really is a common ancestor. As Jackie stated, the genetic code from the LUCA is made up of all of the immortal genes that have been discovered. Immortal genes prove that there is a LUCA. What else would explain the thousand of immortal genes shared by organisms like humans, tomatoes, yeast, archaea, bacteria, etc? There had to have been a common ancestor that passed its genes down to future generations. The future generations separated from each other, but the immortal genes are still here to prove that we all once came from the same ancestor.
As the above comments have discussed, immortal genes are discussed by Carroll as a set of genes that are universal to all organisms. These most likely evolved from the LUCA that is known as our oldest common ancestor. It is theorized that all immortal genes were present in the LUCA and were thus spread to all organisms that descended from it.
ReplyDeleteThe proteins that are encoded from these immortal genes are composed of “letters” that put pressure on the amino acids to stay the same in a changing environment. Old research once hypothesized that, with all the mutations that occur, the human DNA would eventually completely rewrite itself. This was proved wrong because of immortal genes. Some coding is necessary for life. For example, one protein codes for the covalent bonding of atoms. Therefore, some genes have become permanent and necessary in the genetic code. These genes have more of an environmental pressure not to mutate.
For example, this is one reason why there is often more than one code for an amino acid. Sometimes there are three or four different groups of three letters to code for the same amino acid. This makes up for mutations when DNA is being copied. Therefore, the immortal genes have a lower chance of mutation.
Immortal genes are so important to a species that they stop the normal aging process of evolution. Many genes get filtered out or fossilized over time because they are no longer needed in a changing environment. However, immortal genes are important in every environment that the species could ever live in, and, most likely, evolved from the LUCA that needed these genes so long ago.
http://www.sciencemag.org/cgi/content/summary/279/5348/177
http://basketofpuppies-billy.blogspot.com/2009/03/book-club-chapter-3-immortal-genes.html
http://en.wikipedia.org/wiki/Last_universal_ancestor