A.  Daily Blog

Chapter 14 Summary

     Chapter 14 starts off by describing the different kinds of mutations. A mutation is defined as a change in the DNA sequence. Mutations are generally considered agents of disease and other bad things, however mutation is the driving force behind evolution. Without some-what mutation, life would not progress, because some organisms improve via mutation and increases their chances of surviving longer. A mutagen is an agent, chemical or physical, that increases the mutation rate above basal. Examples of physical mutagens include UV rays, an example of a chemical mutagen is radioactive decay. Okay, so back to the different types of mutations. The "first" kind is a non-sense mutation, which is when a normal codon is replaced with a stop codon. This can be very bad because depending on the placement of the new stop codon, the protein will be significantly shorter than it is supposed to be, and this can cause a lot of damage to the cell. Another type of mutation is a type of point mutation (point mutation meaning a change in a single nucleotide) called a missense mutation, where a single nucleotide is changed resulting a completely different codon. The danger of this all depends on context. For example, if a non-polar amino acid is replaced with another non-polar amino acid, it will almost certainly cause no discernible difference in protein function. However, this type of mutation does have potential to be extremely dangerous and is the cause of disease such as sickle-cell anemia. Another type of mutation is a frame shift mutation, where the addition or deletion of a nucleotide causes the cell's reading frame to be erroneous. This is often times very detrimental to the protein, because every codon after the affected site will be wrong. Another type of mutation is the silent mutation, where a nucleotide is changed but the amino acid stays the same, this type of mutation is unnoticeable. In addition, there can be mutations to chromosomes, such as chromosomal trans location and chromosomal amplification. 

     So I just described all of the different mutations that can happen to a cell. But the cell regulates these mutations, and they do their best to help fix these mutations and make sure that they are kept at a minimum. Cells have an infrastructure set up, but when it fails and mutations build upon themselves it often results in cancer. For example, the cell has the ability to repair DNA after it has been damaged. One type of DNA repair is direct repair, where an enzyme completely removes the modification, however this is rare. The most common type is where the altered DNA strand is removed, and a completely new segment is synthesized.

     Another focus in this chapter is oncogenes. Cell division is regulated by growth factors, and these hormones bind to the cell surface bind to the cell surface and initiate the protein cascade that begins the process of cell replication. A mutation in a gene producing cell growth signaling proteins is known as an oncogene, and these oncogenes can often cause abnormally high protein activity. An oncogene may promote cancer by keeping the cell division signaling pathway in a permanent "on" position, which would be very, very bad. A proto-oncogene is a normal gene, that when mutated, becomes an oncogene. 

     Cells also have tumor-suppressor genes which are responsible for preventing cancerous growths. The proteins coded by these genes are usually classified into two functional groups, either proteins that maintain the integrity of the genome or proteins that are negative regulators or inhibitors of cell division. Checkpoint proteins are vital for regulating cell division. Proteins called cyclin and cyclind dependent kinases are responsible for advancing a cell through the four phases of the cell cycle. The p53 gene is one of the most cited examples when explaining the function of checkpoint proteins. p53 is a G1 checkpoint protein. Expression of the p53 gene is induced when DNA is damaged. This prevents a cell from passing through the G1 to the S phase unless it has the DNA is in proper working condition. In addition, if the DNA damage is too severe, the p53 protein will also activate other genes that promote apoptosis. When checkpoint proteins are labeled inactive, bad stuffs happens. 

B.  Useful Materials

Human Mutation- Mermaid Syndrome	This youtube video, which refuses to embed, is about a little girl who has suffered sever mutations, and has "Mermaid Syndrome", and her legs are fused together. I thought that this video was interesting because it shows how tightly regulated the cell cycle needs to be and how errors in mutation can compound upon themselves and create very bad deformities.
	I chose this picture because it shows how truly complicated the regulation of the cell cycle with cyclins and such is. There is a lot going in the picture, and it is important to fully understand all of it to appreciate what the cell has to go through to regulate the cell cycle.
Natural Transformation, Recombination, and Repair.	This article discusses mutation in bacteria.