Name ___________________________________
Chapter 15: Regulation of Gene Expression
Section 15.1: Prokaryotic Transcription Control This is a long one, sorry!
1. What happens when E. coli runs out of tryptophan in a human’s colon? And then what happens when
tryptophan is then added back in?
2. Label the diagram below showing regulation of the tryptophan metabolic pathway. Discuss how the
accumulation of tryptophan inhibits its production two ways
3. How many genes make up the tryptophan operon in E.coli? _____ How many promoters would be
present on mRNA to transcribe the tryptophan operon? ______ How many polypeptides will be
produced from the tryptophan operon? _____
4. How can there be one gene but it produces multiple polypeptides involving the tryptophan operon?
5. What is the advantage of grouping genes of related functions?
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6. Discuss what an operator is and how it controls the expression of a gene grouping.
7. What exactly is an operon?
8. Label the diagram below of Tryptophan operon regulation. Indicate when it is turned on and when it is
off.
9. Now discuss the process shown in the diagram below in your own words so that you can understand it.
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10. What is a regulator, what does it bind to and what does it do to the trp operon?
11. Why is the trp operon not switched off permanently?
12. What is an allosteric protein?
13. How does the tryptophan act as a corepressor in the trp operon?
14. Discuss why the trp operon is a repressible operon.
15. How is the lac operon an inducible operon?
16. What happens to the milk sugar, lactose when intestinal E. coli metabolize it? What enzyme is
necessary?
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17. Identify the 3 genes that are part of the lac operon.
18. Discuss the regulatory gene that controls the lac operon, where is it located and its action?
19. Label the diagram below of the lac operon. Indicate when the gene is turned on and when it is off.
20. How is the regulation of the lac operon different from that of the trp operon?
21. What is the inducer for the lac operon which is an isomer of what compound?
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Videos to watch:
http://highered.mcgraw-hill.com/sites/0072995246/student_view0/chapter7/the_trp_operon.html
Bozeman Science: Operons
Bozmen Science: Gene Regulation
Virtual Cell: Operons
22. Discuss which type of pathways an inducible and a repressible enzyme would be produced in. What is
the advantage of each in energy conservation?
23. How are the lac and trp operons considered to be under negative control?
24. Discuss positive control of genes.
25. Which sugar wins in a war of sugars when both are present in E.coli’s environment AND why?
26. How does E.coli sense the glucose concentration and relay this information to the genome?
27. What is Cyclic AMP (cAMP)?
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28. If glucose levels are low and lactose is present, discuss how cAMP plays a positive control role in the
breakdown of lactose. Label the diagram below in addition to your explanation.
29. If glucose is present along with lactose, what happens to cAMP and the rate of lactose breakdown?
How is this negative control? Label the diagram below in addition to your explanation.
30. Differentiate between the function of the lac repressor and the state of CAP.
31. Discuss the role of CAP other than its involvement with the lac operon
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Section 15.2: Eukaryotic Gene Expression Another long one!
Good video to watch for this next section: http://www.youtube.com/watch?v=kqFa5xgg9wc
1. What fractions of protein coded genes are typically expressed in a human cell at a time? _______
2. What about muscle and nerve cells?
3. Label the diagram below which highlights key stages in the regulation of gene expression in eukaryotes.
Note that the colors of the boxes indicate the key components of the Central Dogma
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4. Explain differential gene expression.
5.
What is the common control point for gene expression and what signals this to occur?
6. Identify the three ways in which the structural organization of chromatin can regulate gene expression.
7. Label the diagram below of a histone, identifying its N-terminus or histone tail. What is the importance
of the histone tails?
8. Discuss histone acetylation and methylation (addition of a methyl group) and their influence on
transcription and the chromatin. Watch the first ½ of this video http://www.youtube.com/watch?v=0jCOGuDcUXg
9. Label the diagram below of histone acetylation and then discuss the influence of acetylation on the
transcription of DNA.
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10. How does DNA methylation of the histone tails or cytosine influence transcription? Give a specific
example.
11. What do multiple cell divisions do to the methylated genes?
12. Discuss epigenetic inheritance and what is being altered
13. Summarize (yes you can list here) the events in eukaryotic transcription.
14. Now add in control elements. What are they and where are they found?
15. Label the diagram below showing gene transcription in eukaryotes.
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16. Where are the control elements for transcription located on a DNA strand? Identify the two different
ones.
17. How do activators influence transcription?
18. Label the diagram below showing the action of enhancers and transcription activators and then
summarize each step in your own words. Watch this Virtual Cell animation http://www.youtube.com/watch?v=vi-zWoobt_Q
19. How do repressors inhibit transcription?
20. Discuss how activators and repressors can alter chromatin structure and thus influence transcription.
21. Discuss how the combination of control elements in the enhancer within a gene is actually regulating
transcription of the various genes making up a genome.
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22. Use the example of the albumin and the crystallin gene to support your answer to #52.
23. Now label the diagram below to further support #53. Discuss what is occurring.
24. Going back to Section 5.6 where cell signaling was covered, give examples of how coordinate control of
dispersed genes in a eukaryotic cell is controlled by chemical signals outside of the cell.
25. Though there are only ~25,000 genes making up the human genome, how do we explain that there are
more than that many proteins produced?
26. Discuss DNA degradation in prokaryotes and eukaryotes.
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27. Identify two ways that translation during the initiation phase can be altered.
28. Discuss ways in which polypeptides are processed following translation.
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