Homework3Key.a12 - PLANT BIOLOGY 113 SPRING 2012 ANSWERS TO...

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P LANT B IOLOGY 113 A NSWERS TO H OMEWORK #3 - P AGE 1 S PRING 2012 ANSWERS TO HOMEWORK QUESTIONS #3 FOR THE SECOND MIDTERM (50,000 points) 1. List steps at which gene expression can be regulated. The processes that can be regulated to control gene expression include: transcription, mRNA stability, translational efficiency, and protein stability. 2. You would like to determine the level at which the expression of the gene encoding an auxin-induced protein is regulated. You do several experiments and obtain the following data about the expression of the gene in auxin-treated and untreated seedlings. Auxin-treated Untreated k PD (min-1) 1 x 10 -5 2 x 10 -5 k S (min-1) 3 x 10 -3 1 x 10 -3 mRNA level (molec/cell) 1,000 10 Based on this data, at what level(s) of expression is the auxin-induced gene regulated? Assuming steady-state conditions, calculate the level of protein encoded by the auxin- regulated gene in auxin-treated and untreated seedlings. Show your calculations. a. The data shows that the auxin-induced gene is regulated at the level of mRNA accumulation, translational efficiency, and protein turnover. mRNA from the auxin-induced gene is present at higher levels and is translated more efficiently in auxin-treated seedlings. Auxin-induced protein is turned over more rapidly in untreated seedlings. b. Auxin-induced protein levels i. dP/dt = k S M - k PD P ii. at steady state, dP/dt = 0 iii. P = (k S /k PD )M c. In auxin-treated seedlings: i. P = 3 x 10 5 molecules/cell d. In untreated seedlings: i. P = 500 molecules/cell 3. You are trying to identify DNA regulatory sequences that control the expression of an ethylene-inducible gene called EIG . The EIG gene is expressed at high levels in ethylene-treated seedlings but at very low levels in untreated seedlings. You make the
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  • Spring '12
  • Harada
  • DNA

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