BIOL 1107 1nd Edition Lecture 22 Outline of Last Lecture I Central Dogma II Three Stages of Transcription III Prokaryote vs Eukaryote IV Mutants Outline of Current Lecture I Mis sense mutation II Non sense III Silent IV Frameshif V Deletion Current Lecture I Mis sense mutation substitution Substitutions that change one amino acid to another one May have little effect on protein new amino acid may have properties similar to those of amino acid it replaces or it may be in a region of protein where exact sequence of amino acids is not essential to protein s function These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II Non sense mutation truncation III point mutation can change a codon for an amino acid into a stop codon It causes translation to be terminated prematurely the resulting polypeptide will be shorter than the polypeptide encoded by the normal gene Nearly all nonsense mutations lead to nonfunctional proteins Silent Some substitutions have no effect on the encoded protein owing to the redundancy of the genetic code For example if 3 CCG 5 on the template strand mutated to 3 CCA 5 the mRNA codon that used to be GGC would be come GGU but a glycine would still be inserted at the proper location in the protein IV A change in a nucleotide pair may transform one codon into another that is translated into the same amino acid Such a change is an example of a silent mutation which has no observable effect on the phenotype Frameshif Will occur whenever the number of nucleotides inserted or deleted is not a multiple of three All the nucleotides that are downstream of the deletion or insertion will be improperly grouped into codons and the result will be extensive missense usually ending sooner or later in nonsense and premature termination Unless the frameshif is very near the end of the gene the pro tein is almost certain to be nonfunctional V Deletion Mutation a genetic aberration in which a part of a chromosome or a sequence of DNA is missing Deletion is the loss of genetic material Any number of nucleotides can be deleted from a single base to an entire piece of chromosome Deletions can be caused by errors in chromosomal crossover during meiosis This causes several serious genetic diseases Deletion also causes frameshif
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