05 Mutations and DNA repair mechanism

05 Mutations and DNA repair mechanism - MUTATIONS AND DNA...

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Isidro C. Medina Jr. Page 1 of 7 Mutation & DNA Repair Mechanism MUTATIONS AND DNA REPAIR MECHANISM Mutations barb2right alterations in gene sequence barb2right can be heritable if the mutation is on the germline (mutations occurring on the DNA of cells that produce the egg and sperm) barb2right involves a change in the shape, structure or nucleotide sequence of the DNA Genetic disorders barb2right a result of alterations of DNA sequences DNA sequence barb2right amino acid sequence barb2right conformation barb2right function Mutations: 1. Spontaneous mutations 2. Induced mutations – caused by mutagens Effect: 1. Lethal 2. Branching in the evolutionary tree or specie diversity Type of mutations according to size: 1. Point Mutations - small or submicroscopic (only one or a small number of nucleotides or bases are affected) 2. Gross Chromosomal Mutations -large-scale chromosome abnormality (seen under the light microscope) POINT MUTATIONS A. SUBSTITUTION : single-base mutations, substitution of one or more nucleotides by the same number of different nucleotides (in most cases, only one) 2 types: TRANSITION : purine to purine TRANSVERSION : purine to pyrimidine pyrimidine to pyrimidine pyrimidine to purine A T A T A T G C G C G C Consequences: 1. Silent mutation - no effect on the amino acid sequence of the protein 2. Missense mutation - results in the incorporation of a different amino acid in the protein. The protein may be functional, partially functional or non-functional 3. Nonsense mutation - results in the premature appearance of a stop codon resulting in the shorter protein that is likely to be non-functional Isidro C. Medina Jr. Page 2 of 7 Mutation & DNA Repair Mechanism B. DELETION : removal of one or more nucleotides in the DNA *effect: frameshift mutation , a shift in the reading frame, which produces a non-functional protein C.
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