Week_4_-_Introduction_to_Mutagenesis - Week 4 -...

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Week 4 - Introduction to Mutagenesis Genetic toxicology is the branch of toxicology that is concerned with the effects of chemical and physical agents on DNA and the genetic processes of living cells. Genetic toxicology broadly encompasses both genotoxicity and mutagenicity - and it is important to differentiate between the two. A mutation is a heritable change in the genotype of a cell and mutagenesis is a term used to describe those process leading to such heritable changes. Genotoxicity , on the other hand, is a term that covers a broad range of endpoints - much broader than mutagenicity. For example, genotoxicity includes such processes as unscheduled DNA synthesis, sister chromatid exchanges and DNA strand breaks. These are not mutagenic processes per se because they are not in themselves heritable (transmissible from cell to cell or generation to generation) but they result in damage to DNA which results in cellular alteration. The development and function of any organism is predominantly controlled by genes. Mutations can lead to changes in the structure or function of an encoded protein or to a decrease or complete loss of its expression. Because a change in the DNA sequence affects all copies of the encoded protein, mutations can be particularly damaging to a cell or organism. In contrast, any alterations in the sequences of RNA or protein molecules that occur during their synthesis are less serious because many copies of each RNA and protein are synthesized. Biologists (and toxicologists) often distinguish between the genotype and phenotype of an organism. Strictly speaking, the entire set of genes carried by an organism is its genotype, whereas the function and physical appearance of an organism is referred to as its phenotype . Genotype usually denotes whether an individual organism carries mutations in a single gene (or a small number of genes), and phenotype denotes the physical and functional consequences of that genotype. Gene mutations are considered to be DNA sequence changes that are limited to a single gene; larger genomic changes are generally referred to as "chromosomal alterations" because they affect more than one gene. Mutations Mutations can involve large or small alterations in DNA. A mutation involving a change in a single base pair (often called a point mutatation ) or a deletion of a few base pairs generally affects the function of a single gene. Changes in a single base pair may produce one of three types of mutation:
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1. missense mutation 2. nonsense mutation 3. frameshift mutation Each of these types of mutations is discussed below: 1. Missense mutation: This type of mutation is a change in one DNA base pair that results in the substitution of one amino acid for another in the protein made by a gene. In this example, the nucleotide adenine is replaced by cytosine in the genetic code,
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This note was uploaded on 02/10/2012 for the course PHY 495 taught by Professor Hess during the Summer '11 term at Alabama.

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Week_4_-_Introduction_to_Mutagenesis - Week 4 -...

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