On this page 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.
Chapter 14 discusses mutation in DNA and how it can be repaired or result in cancer. A mutation is a change in the structure of DNA, possibly affecting the function of DNA. Gene mutations are changes in DNA structure that affect a gene. Mutations can cause two basic changes: the base sequence of a gene is changed or nucleotides are added or deleted. Point mutation affects a single base pair within a sequence. A base pair is either added or removed from the sequence, creating a frameshift. A frameshift causes all the nucleotides, after the mutation point, to be shifted causing the production of a different amino acid sequence. A base mutation is when a single base is substituted by another. These mutations change the structure of that gene and may also affect the amino acid sequence the genes code for. A silent mutation is when the substitution causes no change in the sequence of the resulting amino acid. A nonsense mutation substitutes a base causing the codon to become a stop codon. A missense mutation changes the resulting amino acid of the codon. Mutations can occur in either the somatic cells or the gametes. A mutation in the gametes can be passed on to the offspring. 50% of the gametes carry the mutation. When a mutation occurs in the somatic cells, the offspring does not inherit it. Gene mutations are either spontaneous or induced. Spontaneous mutations occur due to abnormal biological processes, such as error in DNA replication, toxic metabolic products, or changes in nucleotide structure. Induced mutations are caused by environmental agents, either physical or chemical, that alter DNA structure.
Mutations in DNA structure can be repaired, by the means of DNA repair. There are two common repair systems: direct repair and nucleotide excision repair. Direct repair is when an enzyme repairs the single incorrect structure. Nucleotide excision repair removes a segment of DNA, containing the incorrect structure, its removed and a new correct segment is made in its place. If the mutations are not repaired, they can lead to cancer. Cancer is uncontrollable cell division, caused by a mutation in cell development gene. Cancer starts in a single cell. The cell divides undergoing several mutations that cause abnormal cell growth. Those cells then form a tumor. The tumor starts off benign and does not effect surrounding tissue. When mutations cause the tumor to lose growth regulation, it becomes malignant, or cancerous. The cancer spreads when the cells break through into the bloodstream. Some genes, if mutated, promote cancer. A tumor-suppressor gene prevents cancer. If it is mutated, its function is eliminated. A proto-oncogene is a gene, that, if mutated will become an oncogene. Oncogenes, when overactive, contribute to uncontrollable cell growth. Mutations in proto-oncogenes occur if there has been a missense mutation, gene amplification, chromosomal translocation, or insertion of virus genome. To make sure these mutations are not present, there are several checkpoints throughout the cell cycle. At these checkpoints, the DNA is checked for mutations. If the DNA is correct, the cell can proceed with cell division.
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This video explains what the different types of mutations are. It explains the effects of each mutation as well. It describes point mutation and base substitution. It also shows how the mutation affects the structure of DNA. |
| This video shows the direct repair system for DNA repair. The damaged base is removed. The nondamaged strand is used as a template for the new base. |
This video explains the nucleotide excision repair system. When the damage is found, that section of DNA is removed from the strand. That section is remade, now, correctly. |