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an Auxotrophic E

question 24

Multiple Choice

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An auxotrophic E. coli strain requires adenine to grow because of a mutation in a gene for an adenine synthesis enzyme. The following shows part of the wild-type and mutant alleles of the gene, including the start codon. The bottom strand is the template for transcription. $$\begin{array} { c c } \text { ade } 1 ^ { + } \text {wild-type allele } & \text { ade1 } ^ { - } \text {mutant allele } \\\text { 5'...TTATGGGCAAGATCCCA...3' } & \text { 5'....TTA TGGGCTAGATCCCA...3' } \\\text { 3'...AATACCCGTTCTAGGGT...5' } & \text { 3'...AATATGGGCTAGATCCCA...3' }\end{array}$$
-E. coli strains that have both the original ade1^- mutant allele shown above and a mutant allele for a gene that encodes a lysine tRNA are able to make some normal ade1 enzyme. The mutant lysine tRNA allele makes a tRNA that has one base that is different from the wild-type tRNA. Why might the mutant lysine tRNA allele affect overall cell growth?

• A) The mutant tRNA^lysine will occasionally cause translation to continue beyond the normal stop codon on mRNAs that normally use UAG as a stop codon.
• B) The premature stop codon from the ade1^- allele will always cause shortened proteins.
• C) The mutant tRNA will prevent the translational machinery from recognizing the normal stop codon on the mRNA and so will result in incorrect proteins.
• D) The mutant tRNA^lysine will recognize the stop codon on the mutant ade1^- allele and cause the protein to be terminated.
• E) The mutant tRNA^lysine will incorporate a lysine at every UAG stop codon.

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Definitions:

Word Root

The base part of a word, to which affixes (prefixes and suffixes) can be added to create related words.

Kidney

A pair of bean-shaped organs in the renal system that filter waste products from the blood and excrete them as urine.

Urinary System

The organs of the body involved in the production, storage, and excretion of urine.

Urine

A liquid waste product filtered from the blood by the kidneys, stored in the bladder, and expelled from the body through urination.