The Evidence-
As Lawrence Harper says in footnote 22, "Every cell
inherits a full nuclear complement of DNA. That is, all cells in the organism
have the same potential" (187). The only difference why one cell functions
differently than another cell of the same organism is that the "genes in
the cells that are "turned on" or "off" or show
distinctive rates of production of gene products" (187). If
every cell has the same DNA, could it be possible to induce one cell of an
organ to do the same functions as other cells of other organs? Would this be an
effective solution for curing people who have organs that do not function
properly? For example, could a gallbladder be used to produce and as well as
its original function to store bile if a liver was malfunctioning? Why could this idea fail and even be harmful
to an organism? Relate your answer to Gene Expression (Chapter 18) and why cell
differentiation is considered an advantage gained through evolution. Also relate this to the theme of relationship between Structure and
Function.
-Matthew Yang (matt.y.yang2013@gmail.com)
-Matthew Yang (matt.y.yang2013@gmail.com)
Yes, it is true that all cells have the same DNA and the only thing that makes them different is which genes are “turned on or off.” However, is the process of turning certain genes on or off in a cell really that easy? And if it were possible, is it really that practical? Probably not.
ReplyDeleteIn eukaryotes, gene regulation is very complex and multi-dimensional. Turning genes on and off is not as simple as flipping one switch inside the cell. The first layer of gene regulation in eukaryotes is how the DNA is packaged around the histones. Campbell talks about two different ways that genes are regulated via histone packaging: acetylation and methylation (358). Acetylation promotes gene expression and methylation inhibits gene expression. After this first layer there are multiple factors involved in transcription: transcription factors that recognize certain patterns on nucleotides that code to start transcription (359), and enhancers, that ease RNA polymerase in binding to the gene to transcribe RNA (359). After transcription, there are introns (are not expressed), exons (are expresses) and alternative splicing, which means that one RNA’s exon is another RNA’s inton et cetera (362-363). There is also different microRNA and dicers that block translation or cause RNA and proteins to be degraded (365). So when a gene is turned “off” that simply means that during one or more of the steps along this huge process, some factor(s) caused it to not be expressed. So turning certain genes on or off is very difficult. It does happen all the time in nature, but it is not likely to be done artificially.
While using gene regulation may not be practical, there are some alternative solutions to fixing organs that do not function properly. Instead of using cells that have already differentiated and are multiple layers into the whole gene regulation process that happens in eukaryotes, a better solution comes from the use of stem cells that have not yet differentiated. By exposing the stem cells to an environment like whatever organ you want the stem cells to mimic, they will start to express certain genes based on their environment and therefore start to differentiate. Scientists at the Proceedings of the National Academy of Sciences did an experiment in which they used differentiated stem cells that mimicked pancreatic beta cells in diabetic mice. The experiment showed that the mice maintained normal blood levels after getting injected with the differentiated cells to replace cells in their dysfunctional pancreas (Z. Alipio, W Liao, E.J. Roemer, M. Waner, D.C. Ward, and Y. Ma). By letting stem cells pick which genes are expressed based on their environmental demand instead of trying to individually pick which genes are expressed in an already differentiated cell, the results will be much better. Besides, trying to change the cells that already exist can be risky. If a gall bladder is changed to do the job of the liver as well, it may not be as good at doing its own job anymore, which could cause problems. Introducing new stem cells is much safer, and induced pluripotent stem cells can be made from anyone’s skin (stem cells don’t only have to come from embryos).
Brad Tiller (brad.tiller@comcast.net)