A. Daily Blog
This chapter focused on what mutations are, how they occur, and what effects they can have; it also touched on the formation of cancers and on various ways the cell deals with mutations.
A mutation is, quite simply, a change in the genetic material. Mutations can arise from thermodynamically-inevitable natural errors in the cell's DNA replication mechanism. The likelihood of mutations can be increased by chemicals or environments that disrupt the normal effective functioning of the cell's DNA repair or replication processes. Mutations can also arise from direct damage to the DNA, i.e. UV photons causing Thymine-Thymine dimerization.
The types of mutations and how they relate to protein expression have been classified. A missense mutation is a mutation that changes an amino acid; a nonsense mutation introduces an early stop codon; a frameshift mutation inserts or deletes a non-multiple-of-3 number of bases, shifting the "reading frame" of the ribosome and breaking all the amino acids downstream from the mutation; silent mutation change a codon to an equivalent codon and are thus silent. (Although, they can still change the proteome by changing how DNA folds up as it exits the nucleus.)
Cells can identify and fix mutations; a large complex of genes works on this task. In E. coli, one group of genes dedicated to this is Urv{A..D}.
Unfixed mutations are obviously passed down to the cell's mitotic children. This is crucial in a germ cell, because this means that offspring of the organism may inherit the mutation; this is what creates new gene alleles and provides new evolutionary material. Somatic mutations don't get passed off to offspring; nonetheless, they can still cause phenotype changes in the organism.
Cancers commonly arise from mutations. A proto-oncogene may mutate into an oncogene, stimulating uncontrolled cell division. Likewise, a tumor-supressor gene may lose activity due to a mutation, decreasing the effectiveness of DNA preservation and drastically increasing the likelihood of cancer.
B. Useful Materials
www.sciencemag.org/content/291/5507/1284.full.pdf
Interesting article that summarizes much of what we know about human DNA repair genes. There's a very useful table of DNA repair gene functions. I wonder if any systems biologists have researched the interactions of these genes.
http://learn.genetics.utah.edu/archive/mutations/index.html
A cute way of explaining reading frames using English sentences. I'm going to show this to my little brother.
http://highered.mcgraw-hill.com/olc/dl/120082/micro18.swf
This explains how Thymine-Thymine dimerization happens and how it is fixed through a simple flash video with narration. The concept is simple, really; sunlight causes adjacent carbon rings to fuse.
Comments (1)
Derek Weber said
at 12:38 am on Feb 16, 2011
See comments for chapter 13 in regard to chapter summary.
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