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Lecture 4

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York University
Natural Science
NATS 1610

NatsLecture4 Mutations In the living cell, DNA undergoes frequent chemical change, especially when it is being replicated. Most of these changes are quickly repaired. Those that are not result in a mutation. Thus mutation is a failure of DNA repair. A mutation is any change in an organism’s DNA sequence. Proteins, encoded by the genotype, produce the phenotype Hence, DNA mutations affect phenotype only when the mutation is expressed (DNA RNA protein) and the resulting protein functions abnormally. Not all mutations affect the protein’s ability to function and thus do not generate a phenotype. One of the most common types of mutation is the point mutation, a change in a single nucleotide. Point mutations can result from errors in DNA replication or from exposure to mutagenic toxins. Types Silent Mutations - mutations that do not change the amino acid sequence of the protein Missense Mutation - A point mutation that causes a change in the amino acid sequence of the protein Nonsense Mutation - A point mutation that creates a new stop codon Frameshift mutation - is a result of addition or deletion of one or two nucleotides (or multiple of them). - Likely to create a new triplets of nucleotides -New (useless) sequence of protein from the point of the mutation DNA Repair Mutations can result from the incorporation of incorrect bases during DNA replication. Most such spontaneous changes in DNA are temporary because they are immediately corrected by processes collectively called DNA repair. Most damage to DNA is repaired by removal of the damaged bases followed by resynthesis of the excised region. Cells Cell parts: -Cell Membrane -Vesicles -Mitochondria -The Mitochondria have many similarities to bacterial cell: double membrane like some bacteria circular DNA genes without introns (to be discussed) small ribosomes similar size to prokaryotic cells This has led many biologists to theorize that mitochondria are the descendants of some bacteria which was endocytosed by a larger cell billions of years a
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