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DNA & Mutations

DNA & Mutations. Review: Transfer of Information in Cells Errors in Stored Information. A. Review: Transfer of Information in Cells. On average, a cell spends two-thirds of its time in interphase . Interphase is sometimes known as the “resting stage.”

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DNA & Mutations

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  1. DNA & Mutations Review: Transfer of Information in Cells Errors in Stored Information Mr. Peters (c) 2005-06; Revised 2008-09

  2. A. Review: Transfer of Information in Cells • On average, a cell spends two-thirds of its time in interphase. • Interphase is sometimes known as the “resting stage.” • However, this term is misleading because protein synthesis and DNA replication take place during interphase. • The transfer of genetic information from one cell to the next takes place during mitosis or meiosis. Mr. Peters (c) 2005-06; Revised 2008-09

  3. 1. Conceptualization of Genetic Transfer The centromere is the region of the chromosome that is permanently constricted and consists of highly coiled DNA called heterochromatin. Chromosome Genes Centromere Mr. Peters (c) 2005-06; Revised 2008-09

  4. Nucleus Chromosome Cell Parent cells pass their genes to the offspring cells via the chromosome. DNA Mr. Peters (c) 2005-06; Revised 2008-09

  5. 2. Mitosis & Genetic Transfer • During prophase, the nucleolus usually disappears along with the nuclear membrane. • The centrioles replicate during interphase, so that at the beginning of mitosis a cell has two centrioles. • Each offspring receives a pair of centrioles from the parent cell. • Mitosis and meiosis refer to nuclear division. • Cytokinesis is the actual cell division (which takes place after telophase). • Like meiosis, crossing over can take place in mitosis, though it is a rarer occurrence. • Scientists speculate that regulator genes determine which genes are “turned on or off” during mitosis. • It is thought that this “switching on/off” of genes may help to explain the nature of cancer and other mutations. Mr. Peters (c) 2005-06; Revised 2008-09

  6. 3. Meiosis & Genetic Transfer • The first meiotic division separates the homologous chromatids in each tetrad, and the second division separates the two chromatids of each chromatid pair. • It is during these divisions that genetic transfer occurs in sex cells, and it is at these junctures that genetic mutation can occur due to nondisjunction. • It is through meiosis that the great variety within a species is produced. Mr. Peters (c) 2005-06; Revised 2008-09

  7. B. Errors in Stored Information • As you have learned, genetic mutations can occur through: • The deletion of genes in a chromosome. • The addition of genes in a chromosome. • The inversion of genes in a chromosome. • Nondisjunction. • Genetic mutations are rarely beneficial, and sometimes lethal. • Mutations do not occur only on chromosomes, they can also occur through changes in the arrangement of nitrogen bases on DNA. Mr. Peters (c) 2005-06; Revised 2008-09

  8. Point vs. Frameshift Mutation • Point mutation involves the substitution of one DNA nucleotide for another (an inversion). • Sickle cell anemia is an example of point mutation. • Sickle cell anemia results in a mis-shapen blood cell, where the double-concavity of a blood cell is compromised, thereby providing less oxygen absorption, and impairing other cellular functions. Mr. Peters (c) 2005-06; Revised 2008-09

  9. Point vs. Frameshift Mutation • Frameshift mutation involves the deletion or addition of nucleotides (nitrogen base, sugar, and phosphate group), so that every codon (three base code for an amino acid) beyond the point of insertion or deletion is read incorrectly during translation (the process by which proteins are synthesize using the DNA instructions encoded in the mRNA). • B-thalessemia is an example of a frameshift mutation. • Thalassemia is a genetic disorder in which there is decreased production of one of the globin chains found in hemoglobin. This can cause anemia. Anemia causes fatigue and stress on bodily organs. Mr. Peters (c) 2005-06; Revised 2008-09

  10. Changes in base pair arrangement are often due to the presence of mutagenic agents such as cosmic rays, X-rays, UV radiation, and chemicals. • Because the arrangement of base pairs code for certain amino acids, and amino acids in a certain order code for particular proteins, and proteins carry out specific cellular functions, cell function is impaired or completely destroyed as a result of the mutation. • Mutations can occur because: • There is a shortage of a particular nucleotide. • One nitrogen base is substituted for another. Mr. Peters (c) 2005-06; Revised 2008-09

  11. In the Apr. 25/06 Winnipeg Free Press, an article was written that studies link a common herbicide (2-4-D) used on lawns with cancer in humans. • If this evidence bears out, here is yet another example of how the everyday use of chemicals carries serious health and cancer risks. • When mutations occur, they are repeated each time the cell divides. • A mutation in an egg or sperm cell will lead to permanent change in the characteristics of offspring. • This is why mutagenic agents are particularly dangerous for pregnant women, especially during the first trimester of pregnancy. Mr. Peters (c) 2005-06; Revised 2008-09

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