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Chapter 14 Blog: Mutation, DNA Repair, and Cancer (Ambika)

Page history last edited by Ambika Sharma 12 years, 10 months ago

In the first section of this page, you will write a daily summary of that day's class.  For example in  your chapter 2 blog, your first entry should be titled 9/3/10.  You should then write a one or two paragraph summary of that day's lecture, outlining the major points.  In the second section, you are required to add two items (link to a website, video, animation, student-created slide show, student-created PowerPoint presentation) and one journal article pertaining to a topic in this chapter.  A one-paragraph summary must accompany each item describing the main idea and how it applies to the lecture topic.  Please see the PBWorks help guide for assistance embedding video and other items directly in the page.  I will also produce a how-to video on using tables to wrap text around items and other useful tips.  Please see the syllabus for organization and grading details.


A.  Daily Blog


     As we have learned in previous chapters, well, we should all remember, that DNA structure can ultimately affect DNA function. Chapter 14 focuses on the different types mutations that can occur which affect DNA structure, which ultimately, affects DNA function. So what are gene mutations? Gene mutations are exactly what they sound like! They are relatively small changes in DNA structure that alter a particular gene. Many people believe that mutations are a bad thing. Well, let me get one thing straight... THOSE PEOPLE ARE WACK, MAN. Mutations help evolution!! Without mutations, we would technically, well pretty much, not be alive. These mutations can cause two basic types of changes to a gene. They can either a) change the base sequence of the gene, or b) add or remove one or more nucleotides from the gene.

     I'm sure you all are DYING to hear some types of mutations so let's do just that! The first type of mutation, a point mutation, affects only a single base pair within the DNA. For example, the unaltered DNA sequence could read 'CCGTA' but after a base substitution, it could read 'CCGAA'. In this case, the thymine was replaced with adenine. Point mutations can also involve the addition or deletion of a single base pair. Another type of mutation is the silent mutation. These mutations are exactly what they sound like: they change the nucleotide sequence but they do NOT alter the amino acid sequence of the polypeptide. So pretty much, they cause no change. The next mutation, the missense mutation, changes one amino acid in a polypeptide sequence. However, this may not necessarily alter protein function. One particular missense mutation we focused on was sickle-cell disease. This disease involves a missense mutation in the β-globin gene, which encodes for a subunit of hemoglobin, changes the sixth amino acid in the β-globin polypeptide from a glutamic acid to a valine. Another mutation we learned about is a nonsense mutation. This mutation involves a change from a normal codon to a stop/termination codon. This causes the production of a truncated polypeptide. What does that mean? A truncated polypeptide is just a fancy way of saying that the polypeptide is less likely to function properly. Finally, the last mutation we learned about is the frameshift mutation. The frameshift mutation involves the addition of deletion of nucleotides that are not in multiples of three nucleotides. This means that a nucleotide could add or delete one, two, four or five nucleotides. This tends to shift the reading frame. 

     The next topic covered in Chapter 14 was DNA repair. There are three different types of DNA repair. These three types are: Direct repair, Base excision and nucleotide excision repair (BER and NER), and Methyl-directed mismatch repair. Direct repair occurs when an enzyme recognizes an incorrect structure and directly converts it to the correct structure. NER occurs when an abnormal base is recognized and then a portion of DNA that contains the mistake is removed while the other strand of DNA is used to synthesize a new portion. Methyl-directed mismatch repair is similar to NER, but it repairs mismatched pairs of nucleotides, rather than abnormal ones. However, it removes a portion of DNA and then uses the other strand to synthesize a new one.

     The last topic that was covered in Chapter 14 was a disease that is deadly... cancer. Cancer is a disease of multicellular organisms characterized by uncontrolled cell division. Cancer cells have a gene that is a mutant gene.  This type of mutant gene is called an oncogene. However, when a gene is normal and is trying to prevent cancer it is called a tumor-suppressor gene. So, when a mutation occurs and eliminates the function of the gene, cancer occurs. Cancer occurs in a few steps and what I just mentioned happens to be the first step (a mutation occurs in a DNA repair gene). The next genes to become mutated are the proto-oncogenes. These genes tend to encode for proteins that are involved in cell growth, thus their name. These genes become oncogenes if mutated. This eventually causes a benign tumor to arise. A benign tumor is a tumor that does not spread throughout the body. Unfortunately, this tumor will eventually become malignant tumors after mutations occur and cause the cells in the tumor to lose their normal growth regulation. At this point, the individual has cancer :o( These cancerous tissues will invade healthy tissues through a process called metastasis. This is deadly!


B.  Useful Materials


 Useful Video
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This video talks about the mismatch repair. As we discussed in class, this

repairs mismatched pairs of nucleotides. I think this video is pretty helpful

however, the animations could be better!


Another Useful Video
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A huge part of chapter 14 deals with cancer and cancerous cells. I feel like

this video is a great video because instead just giving facts about cancer,

it goes into great depth about what cancer REALLY is. The animations being

shown really make it a lot easier to understand the information being told as

well. I think everyone should take the time to watch this video! It is of great help.


Useful Article

Molecular Analysis of Fanconi Anemia and Mismatch Repair Genes in Patients with Colorectal Carcinoma.


This is an interesting article. It focuses on a study that was conducted on 206 consecutively-collected patients with colorectal carcinoma. There were screened for germline mutations in the principal DNA mismatch repair genes (we talked about this!) Mutation analysis performed on these patients by denaturing high-performance liquid chromatography. Paraffin-embedded tumor tissues were evaluated for gene expression by immunohistochemistry. The results indicate that the mismatch DNA repair remains the main mechanism to be altered at both germline and somatic levels. The results also indicate that functional impairments of mismatch DNA repair and FA-related repair may represent two different pathogenetic alterations which are concurring in colorectal cancer progression.




Comments (1)

Derek Weber said

at 12:41 am on Feb 16, 2011

I like the use of bold in the summary. Please see comments for chapter 13.

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