5.1 Two classes of polar mutations can be isolated in the lac operon. One class

Question

5.1 Two classes of polar mutations can be isolated in the lac operon. One class of pola r mutations maps upstream of the lacZ gene and no nonsense mutations are found includes nonsense mutations. (3 points/question. 15 points in t in this class. A second class of polar mutations that maps within the lacZ gene a. What is polarity? (Give an example using the lac operon.) shich Polarity a.fesh moleales unth detach. Testers nher.-f b. What is the most likely cause of each of the two classes of mutations.? How would you determine if a mutation was a nonsense mutation without directly sequencing the DNA? c. d. Why are no nonsense mutations found among the first class of mutations? What causes the polarity of the two different classes of mutations? e.

Explanation / Answer

c).

Nonsense mutations are defined as mutation in a sense codon of gene or DNA, leads to a stop codon. This is the main reason one cannot sequence the DNA to identify the nonsense mutation. This nonsense mutation results into incomplete or non-functional protein is formed. Prior to that we know how many amino acids it contains, So that we can use the nonsense suppressors to continue the process of translation. ( these suppressors work on t-RNA, and insert different amino acid instead of termination).

D). If any nonsense mutation found above the sequence it will not affect the mRNA or Protein sequence because it is not transcribed into mRNA. Upstream means that the nucleotides present above that the first nucleotide of the gene (starting nucleotide to be transcribed)

E).

1. First class directly prevents the transcription.

2. 2nd class cause translation termination because Rho binds to the untranslated sequences, so these two result into polarity.

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