On pages 44-46 of
Your Inner Fish, Shubin begins to discuss "handy genes." Give an in-depth explanation of DNA and gene expression. Include in your discussion the important role that "genetic switches" play in the biological assembly and make-up of humans and other organisms.
Matt Kim
(matthewkim0803@gmail.com)
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ReplyDeleteThere are two basic steps in gene expression of DNA. The first is transcription, which is "the synthesis of RNA under thd direction of DNA" (Campbell 328). A DNA strand serves as a template for assembling a complementary sequence of RNA nucleotides. Thu, the resulting RNA molecule is a "faithful transcript of the gene's protein-building instructions" (Campbell 328). This new RNA molecule is called a messenger RNA because it takes genetic information from the DNA to the protein-synthesizing part of the cell (ribosome). In eukaryotic cells, since the mRNA must travel outside of the nucleus, RNA processing must take place in order to protect the mRNA and facilitate its movement out of the nucelus. Also, large portions calls introns can be spliced out of the RNA molecule that will not be expressed later. Once the mRNA is ready and leaves the nucleus, it will attach to a ribosome. Codons are then translated into amino acids, one by one. The interpresters are tRNA molecules, each type with a specific anticodon at one end and a corresponding amino acid at the other. A tRNA adds its amino acid to a growing polypeptide chain, which eventually leaves the ribosome and folds into its final conformation as a protein after being processed in the ER and the Golgi apparatus.
ReplyDeleteThe genetic switches that Shubin discusses are individual genes that turn "on and off inside each cell during our development" (Shubin 46). Overall, these genes, through the processes of transcription and translation, are able to help assemble us as we develop, even from a single cell. Being able to identify specific genetic switches and understanding gene expression allows scientists to "compare the activity of different genes to assess what kinds of changes are involved in the origin of new organs" (Shubin 46). For example, we can compare the genes active in the development of a fish fin to those active in the development of a human hand, and find the genetic differences between fins and limbs. Thus, we can identify the genetic switches that may have changed during the origin of limbs. This type of information adds to our knowledge of evolution from species to species due to natural selection.
Genetic switches that are different in humans can also be studied to better understand the evolution of our own species. A study done at the Stanford University School of Medicine showed that a genetic variation of the hormone involved in the secretion of insulin occurs in some populations more than others. This "genetic switch" that affects diabetes may have occurred some 2,000 to 12,000 years ago, scientists say, when the population shifted from hunter-gatherers to a more agricultural-based society. These studies that examine genetic switches within the human population can be used to help treat diseases like diabetes, along with helping us understand our evolutionary history to a fuller extent.
http://med.stanford.edu/ism/2011/february/diabetes.html-Evolution led to genetic variation that may affect diabetes, scientist says
Hannah Kay (hgkay@aol.com)
Although Hannah gives a decent explanation on gene expression, she did not provide an in-depth explanation about the history of DNA, and what DNA actually is. DNA, short for deoxyribonucleic acid, are basically molecules which are responsible for the production of proteins, RNA molecules, and the production of more DNA molecules. The structure of DNA was a great mystery to scientists; Pauling and Corey had suggested that DNA molecules actually have “three intertwined chains, with the phosphates near the fibre axis, and the bases on the outside (http://www.pnas.org/site/misc/classics1.shtml). However, this model was unsatisfactory in various ways, and was not capable of answering every question there was about the structure of DNA. In April 1953, James Watson and Francis Crick suggested that the structure of a DNA is actually a double-helix, providing a radically different perspective to the idea of how they looked like (http://www.nature.com/nature/dna50/watsoncrick.pdf). Currently, Watson and Crick’s double-helix structure of the DNA is widely accepted. Their studies have allowed other scientists to discover how DNA replication and protein synthesis were accomplished.
ReplyDeleteGene expression is “the process by which DNA directs the synthesis of proteins” (Campbell, 325). As Hannah briefly mentions, the basic processes which accomplish gene expression are transcription and translation. Although she has covered the basic mechanisms of gene expression, I would like to provide a good analogy to explain gene expression- cooking. Imagine that a chef has a cookbook full of recipes. When a chef cooks, they first copy the recipe down on a piece of paper so the book does not become ruined in some way. He then brings it into the kitchen. From there, he follows the instructions that he wrote on the piece of paper to create a delicious dinner. In this analogy the cookbook would be the DNA molecules in the nucleus. The information that is written on the DNA are transcribed into RNA molecules (the piece of paper) by RNA polymerase, and then sent out of the nucleus and into the cytoplasm of the cell (the kitchen). From there, the RNA molecule is translated by tRNA and the ribosome, which read the codons on the mRNA to assemble a protein (the dinner) from amino acids (the ingredients).
Like Hannah, I believe that the “genetic switches” that Neil Shubin refers to are the genes that regulate gene expression in a developing embryo. An example of a genetic switch that Shubin directly refers to would be the Sonic Hedgehog gene. He describes the role of the hedgehog gene in embryos when he writes, “Whole batteries of genes are turned on and off during [embryonic] development, and this pattern of gene activity serves to demarcate the different regions of the [embryo]” (Shubin, 52). Another great example would be ZPA. When Gasseling, Saunders, and Zwilling created a wing bud with extra ZPA, the result was a mirror image duplication of the wing. In this manner, genes play a critical role in determining the body plan of the developing embryo.
Works Consulted:
Campbell Biology
Your Inner Fish
http://www.pnas.org/site/misc/classics1.shtml
http://www.nature.com/nature/dna50/watsoncrick.pdf
(Keigo Tanaka; tanakarus3@hotmail.com)