Wrap-Up Questions

1. List the mechanisms that can be used to regulate gene expression in eukaryotes.

2. For each of the following lac operon genotypes, would β-galactosidase be expressed?

1. I⁺, O⁺, Z⁺, Y⁺ (no glucose, no lactose)
2. I⁺, O⁺, Z⁺, Y⁺ (no glucose, high lactose)
3. I⁺, O⁺, Z⁺, Y⁺ (high glucose, no lactose)
4. I⁺, O⁺, Z⁺, Y⁺ (high glucose, high lactose)
5. I⁺, O⁺, Z^–, Y⁺ (no glucose, no lactose)
6. I⁺, O⁺, Z^–, Y⁺ (high glucose, high lactose)
7. I⁺, O⁺, Z⁺, Y^– (high glucose, high lactose)
8. I⁺, O^c, Z⁺, Y⁺ (no glucose, no lactose)
9. I⁺, O^c,Z⁺, Y⁺ (no glucose, high lactose)
10. I⁺, O^c, Z⁺, Y⁺ (high glucose, no lactose)
11. I⁺, O^c, Z⁺, Y⁺ (high glucose, high lactose)
12. I^–, O⁺, Z⁺, Y⁺ (no glucose, no lactose)
13. I^–, O⁺, Z⁺, Y⁺ (no glucose, high lactose)
14. I^–, O⁺, Z⁺, Y⁺ (high glucose, no lactose)
15. I^–, O⁺, Z⁺, Y⁺ (high glucose, high lactose)
16. I^s, O⁺, Z⁺, Y⁺ (no glucose, no lactose)
17. I^s, O⁺, Z⁺, Y⁺ (no glucose, high lactose)
18. I^s, O⁺, Z⁺, Y⁺ (high glucose, no lactose)
19. I^s, O⁺, Z⁺, Y⁺ (high glucose, high lactose)

3. In the E. coli strains listed below, some genes are present on both the chromosome and the extrachromosomal F-factor episome. The genotypes of the chromosome and episome are separated by a slash. Would β-galactosidase be expressed in each of these strains?  All of the strains are grown in media that lack glucose.

1. I⁺, O⁺, Z⁺, Y⁺ / O^–, Z^–, Y^–   (high lactose)
2. I⁺, O⁺, Z⁺, Y⁺ / O^–, Z^–, Y^–   (no lactose)
3. I⁺, O⁺, Z^–, Y⁺ / O^–, Z⁺, Y⁺   (high lactose)
4. I⁺, O⁺, Z^–, Y⁺ / O^–, Z⁺, Y⁺ (no lactose)
5. I⁺, O⁺, Z^–, Y⁺ / I^–, O⁺, Z⁺, Y⁺   (high lactose)
6. I⁺, O⁺, Z^–, Y⁺ / I^–, O⁺, Z⁺, Y⁺   (no lactose)
7. I^–, O⁺, Z⁺, Y⁺ / I⁺, O⁺, Z^–, Y⁺   (high lactose)
8. I^–, O⁺, Z⁺, Y⁺ / I⁺, O⁺, Z^–, Y⁺   (no lactose)
9. I⁺, O^c, Z⁺, Y⁺ / I⁺, O⁺, Z^–, Y⁺   (high lactose)
10. I⁺, O^c, Z⁺, Y⁺ / I⁺, O⁺, Z^–, Y⁺   (no lactose)
11. I⁺, O⁺, Z^–, Y⁺ / I⁺, O^c, Z⁺, Y⁺   (high lactose)
12. I⁺, O⁺, Z^–, Y⁺ / I⁺, O^c, Z⁺, Y⁺   (no lactose)
13. I⁺, O⁺, Z^–, Y⁺ / I^s, O⁺, Z⁺, Y⁺   (high lactose)
14. I⁺, O⁺, Z^–, Y⁺ / I^s, O⁺, Z⁺, Y⁺   (no lactose)
15. I^s, O⁺, Z⁺, Y⁺ / I⁺, O⁺, Z^–, Y⁺   (high lactose)
16. I^s, O⁺, Z⁺, Y⁺ / I⁺, O⁺, Z^–, Y⁺   (no lactose)

4. What would be the effect of the following loss-of-function mutations on the expression of the lac operon?

1. loss-of-function of adenylate cyclase
2. loss of DNA binding ability of CAP
3. loss of cAMP binding ability of CAP
4. mutation of CAP binding site (CBS) cis-element so that CAP could not bind

5. How are eukaryotic and prokaryotic gene regulation systems similar? How are they different?

6. The trp operon leader has multiple tryptophan codons in a row.

1. What do you think would be the impact to transcription of the trp operon, if a mutation changed those codons from UGG to UGA?
2. What do you think would be the impact to transcription of the trp operon, if a mutation changed the tryptophan codons from UGG to UGC? Explain your reasoning.