回顧問題不定期更新 Study Questions are Made by Prof. Cruz & Prof. Moore from Oberlin College & Conservatory?

Lectures 23 & 24: Protein Synthesis/Gene Expression and Flowering Signal Cascades

1. In what organelle of the cell do transcription factors work? Why are transcription factors important for gene expression?

2. The template strand is given below for a portion of a gene. The first position in the sequence corresponds to the first position of the first codon in the coding region of the gene. Also, the nucleotides are numbered from 1 to 45, from left to right (the numbers are given in increments of 5 above the nucleotides; for example, see if you can find position 31—there should be an A at that position). Using this sequence, answer the questions below.

a) What would be the sequence of the mRNA made from this strand of DNA?

b) What would be the sequence of the coding strand of DNA, given this template strand?

c) What would be the primary structure of the polypeptide made from this coding sequence?

d) Circle the location of the stop codon in the mRNA sequence made from this template strand.

e) What kind of mutation results if we change the C in nucleotide position 24 to a T?

f) What kind of mutation results if we change the T in nucleotide position 13 to an A?

g) What kind of mutation results if we change the T in nucleotide position 10 to a G?

h) Which deletion would be worse: the deletion of nucleotide positions 7-9, or the deletion of nucleotide positions 18-19? Why? Predict the new amino acid sequence under each scenario.

3. Why are most mutations at the third codon position silent?

4. Could mutations in the regions of the gene outside of the coding region have deleterious effects on the organism? Explain your answer.

5. Which is more likely to be deleterious —a 3-nucleotide deletion in the gene sequence that corresponds to the active site of an enzyme, or a 3-nucleotide deletion located somewhere else in the gene for that enzyme? Explain.

6. Imagine that you observe the following homeotic mutants in an Arabidopsis flower. Predict the gene expression pattern in ABCE-class genes across all 4 whorls for these flowers (you can ignore the E-class genes for the purposes of this question).

a) petal:petal:petal:pistil

b) sepal:sepal:petal:petal

c) stamen:petal:petal:stamen

7. Imagine that we could selectively block transcription of the proteins involved the flowering Signal cascade (in other words, imagine that we could control gene expression of the individual genes involved in flowering at will). Under each of the following circumstances, predict whether the plant will flower and if so, predict what the flower will look like.

a) if we blocked LFY expression

b) if we blocked CO expression

c) if we blocked B-class gene expression (you can ignore the effects of the E-class genes)

d) if we blocked FD expression

8. Grafting is a process in which the stem of one plant is sliced off (very cleanly) and inserted into a notch that is excised out of another (very clean) slice of a separate plant of the same species (look this up online—it’s pretty cool). This allows the xylem and phloem of the two plants to grow together; i.e. the wound heals and the two stems are now permanently joined. In fact, this process is used in all apple and grape cultivation. The roots of commercial apple trees and commercial grapevines are always of a different individual than the stems; in this manner it is possible to cultivate the same breeds of apples or grapes without using seeds, which would mix up genetic variation. Hence, if one wants to have exactly the same apple characteristics but wants a new individual tree, the only way to do this is to take a cutting of a mature apple tree and graft it onto the rootstock of another young apple tree.

Imagine that you grafted a flowering stem from one apple tree directly into a young, non- flowering apple tree. When you do this, you notice that a week later, the non-flowering parts of the tree begin to flower. Why does grafting a plant with flowers onto a plant without flowers induce inflorescence production in the plant without flowers? In other words, how is this possible?

9. What do all of the proteins involved in the flowering Signal cascade (i.e. all of the proteins from CO to the proteins made by the ABCE-class genes) share in common?

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