Stop codon


Q.

The following DNA sequence occurs near the middle of the coding region of a gene.

DNA 5' A A T G A A T G G* G A G C C T G A A G G A 3'

There is a G to A base change at the position marked with an asterisk. Consequently, a codon normally encoding an amino acid becomes a stop codon.

1. How will this alteration influence DNA replication?

2. How will this alteration influence transcription?

3. How will this alteration influence translation?


Special Instructions

This is a 3 part question.  Responses to each part should be collected in a separate text box.

Background Information

This question was previously referred to as "Central Dogma".

This set of items have been converted from the Genetics Concept Assessment by Smith et al.

For the constructed respons version, students are given one set-up paragraph, then given three separate question prompts (one prompt about each central dogma process) and separate text boxes to input their response.

Original items:

#11:  The following DNA sequence (coding strand) occurs near the middle of the coding region of a gene.

DNA

    50
5'-A A T G A A T G G G A G C C T G A A G G A G -3'

The corresponding mRNA sequence is shown below. Note that the coding strand of DNA has the same sequence as the mRNA, except that there are U's in the mRNA where there are T's in the DNA. The first triplet of nucleotides AAU (underlined) is in frame for coding, and encodes Asparagine as the codon table indicates.

mRNA

   50
5'-A A U G A A U G G G A G C C U G A A G G A G -3'

Which of the following DNA mutations is almost certain to result in a shorter than normal mRNA?

a) A¨G at position 50
b) G¨A at position 53
c) C¨A at position 58
d) None of the above

#12  For the same DNA sequence, which of the following DNA mutations is almost certain to result in a shorter than normal protein?

a) T¨C at position 59
b) A¨G at position 61
c) Insertion of a G after the G at position 54
d) None of the above


Question Instructions

We recommend that you administer these questions as homework and preface the question with these instructions for students:

"For the following question, please respond to the best of your knowledge and using only the information in the question and what you know. Please do not refer to any outside sources (textbooks, notes, internet, etc.). Any reasonable attempt to answer the question will be awarded full credit."

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