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Genetics 301 Quiz #8
Spring 2003br> Class week 10

Chemical Z is a newly developed chemical which is being considered as a food additive. What is your interpretation about the mode of action of the chemical and its safety, based on the following results using the Ames test? (5 pts).

Treatment Mean number of his+ colonies detected per million cells plated on minimal medium

His- mutant alone 5

His- mutant +

Chemical Z 2,000

His- mutant +

Chemical Z +

Rat liver extract 2,000

The chemical induces mutations even without activation by the rat liver extract. It is dangerous and should not be used as a food additive. It would probably cause cancer in tests with animals.

Draw a simple diagram (labeling only introns, exons and poly A tail) of the appearance of a mature, processed eukaryotic messnger RNA hybridized to the DNA from which it was transcribed. Assume that there are three introns located within the gene, the four coding regions are each 300 bases in length, the first intron appears after the first coding region, the introns are each 3 kilobases in length, the 5’ and 3’ untranslated regions (which are, however, transcribed) are each 200 bases in length and the polyA tail is 300 bases long. (3 pts.).

DNA- has all of the elements in the RNA except the poly A tail, plus it has three 3 kb introns

Additional 3 kb loops at X sites

-------------------- X --------- X ---------- X ------------------- (no poly A tail)

______________________________________________________

200 1200 bases coding 200 5’ UTR 300 poly A tail

5’UTR

Processed RNA

How many amino acids would be coded for in the corresponding protein? (2 pts.)

Four coding regions X 300 bases each = 1200 bases. 1200 bases/ 3 bases per codon = 400 amino acids.