Essential Elements of Biochemistry BCHM 3050 Dr Srikripa Chandrasekaran Lecture 3 25 15 Notes Regulation of Transcription continued I Trp operon A The trp operon is the reverse of the lac operon B The trp operon is turned on when you do not have any tryptophan because the trp operon synthesizes or makes tryptophan C Trp operon is off when you have tryptophan D Trp operon is on when you do not have tryptophan E The trp operon is a repressor 1 DNA Mutations I Mutations A Mutation occurs when the replication machinery puts an incorrect base into the sequence B Sometimes you can have a mistake and it is never corrected C D 5 types of point mutations In humans every 24 hours we replicate our DNA once 1 Missense 2 Silent 3 Nonsense 4 Insertion 5 Deletion E Substitution is substituting one base for another base completely F Missense mutation a change in a base causes one amino acid to change into another G Silent mutation a change in a base that does not change the amino acid that is coded no changes in amino acids so this type of mutation is difficult to detect does not affect the protein H Nonsense mutation a change in a base that causes the coding of a premature or early STOP codon Insertion and deletion are frameshift mutations I J Missense silent and nonsense mutations are substitution mutations K The best mutation to have is silent then missense Silent mutation does not change any amino acids and missense mutation changes only one amino acid A nonsense mutation completely cuts part of the DNA off since it stops the process early Frameshift mutations change multiple amino acids Chromosome level mutations A A lot of inversions and translocations happen during cancer B Down Syndrome is an example of aneuploidy Transition and transversion mutations A Transition mutation a purine replaced by a purine or a pyrimidine replaced by a pyrimidine B 80 of mutations are transition mutations C Transversion mutation a purine replaced by a pyrimidine or a pyrimidine replaced by a purine II III 2
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