Ch 18 Reading Guide- Answers

AP Biology Reading Guide Fred and Theresa Holtzclaw Copyright © 2010 Pearson EducationName___________________________________ Date___________________ Period_______ Chapter 18: Regulation of Gene Expression Overview The overview for Chapter 18 introduces the idea that while all cells of an organism have all genes in the genome, not all genes are expressed in every cell. What regulates gene expression? Gene expression in prokaryotic cells differs from that in eukaryotic cells. How do disruptions in gene regulation lead to cancer? This chapter gives you a look at how genes are expressed and modulated. Concept 18.1 Bacteria often respond to environmental change by regulating transcription 1. All genes are not “on” all the time. Using the metabolic needs of E. coli, explain why not. E. coli works by activating a metabolic pathway that makes tryptophan. This only happens when the human does not eat any meat. Once meat is eaten, E. coli stops to save its energy for when the meat is gone. 2. What are the two main ways of controlling metabolism in bacterial cells?  Cells can adjust the activity of enzymes already present with chemical cues through feedback inhibition  Cells can adjust the production level of the genes encoding the enzymes 3. Feedback inhibition is a recurring mechanism throughout biological systems. In the case of E. coli regulating tryptophan synthesis, is it positive or negative inhibition? Explain your choice. It is negative inhibition because the accumulation of the product stops the enzyme from catalyzing it. 4. What is a promoter? A promoter is a sequence of DNA nucleotides where RNA polymerase binds to in order to start transcription. 5. What is the operator? What does it do? An operator is a sequence of nucleotides near the start of an operon where an active repressor can attach. It prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon. 6. What is an operon? An operon is a unit of genetic function found in bacteria and phages. It includes a promoter, an operator, and the genes they control. 7. List the three components of an operon, and explain the role of each one.  Promoter- starts transcription  Operator- On/Off switch- synthesizes enzymes at once  Genes they control- determines whether or not a certain amino acid will be coded for 8. How does a repressor protein work? A repressor protein binds to the operator and blocks the attachment of RNA polymerase tot the promoter, which prevents transcription of a gene. 9. What are regulatory genes? Regulatory genes code for a protein that controls the transcription of another gene or group of genes. 10. Distinguish between inducible and repressible operons, and describe one example of each type.  Repressible operons are usually on but can be inhibited when a specific small molecule binds allosterically to a regulatory protein. (ex: tryptophan operon)  An inducible operon is usually off but can be stimulated when a specific small molecule interacts with regulatory proteins. (ex: lactose operon) 1 13. The trp operon is inactive by itself and requires tryptophan as a compressor.2 Eukaryotic gene expression can be regulated at any stage 18. Even though all cells of an organism have the same genes. Explain why CAP binding and stimulation of gene expression is positive regulation. What happens when a repressor is bound to the operator? The gene is not transcribed because the RNA polymerase cannot bind. Concept 18. which is a positive regulation because it is perpetually increasing. What percentage of the genes of a typical human cell is expressed at any given time? 20% 20. cAMP concentration lowers. Label this sketch of the lac operon with the terms at right. CAP detaches from the operon because there isn’t enough cAMP to hold it. 17. 19. (the operon is off) 14. there is differential gene expression. (Remember that compare means “to tell how they are similar. What is CAP? How does CAP work? CAP is Catabolic Activator Protein. making them negative regulators. The lac operon is active by itself.11. What is the common control point of gene expression for all organisms? Transcription 2 . How can both repressible and inducible operons be negative regulators? Their products inhibit the production of more products. cAMP. Operon genes Operon RNA polymerase mRNA Repressor protein Operator Repressor Regulatory gene Inducer 12. What does this mean? The expression of different genes by cells with the same genome are showing. When the amount of glucose in a cell increases. cAMP is attached to the regulatory protein. Describe the relationship between glucose supply. 15. 16.”) Both operons code for an allosteric repressor protein that can switch on and off. Compare and contrast the lac operon and the trp operon.” and contrast means “to tell how they are different. This is a regulatory protein that binds to DNA and stimulates transcription of a gene. CAP binding increases the rate of transcription (gene expression). and CAP. Know the function of each structure. enhancer. Operons have not been found in eukaryotic cells.21. Euchromatin (“true chromatin”) is lightly condensed and help regulate gene expression. The inactive mammalian X chromosome is heavily methylated. What is DNA methylation? What role may it play in gene expression? Addition of a methyl group on the DNA bases of eukaryotes makes cells heavier and turns off genes. promoter. 23. Then place your explanation to the right of the figure. Use the sketch below to explain how enhancers and activators interact with transcription factors to affect gene expression. What occurs in histone acetylation? How does it affect gene expression? Acetyl groups are attached to lysines in histone tails. functionally related genes are usually clustered in a single operon. RNA polymerase II. Explain what is meant by epigenetic inheritance. 26. Distinguish between heterochromatin and euchromatin as to their structure and activity. This promotes transcription initiation by giving proteins easier access to the genes. What has been found to be the case in eukaryotes? 29. In prokaryotes. What is genomic imprinting. activators. 27. and the genes coding for the enzymes of a particular metabolic pathway are often scattered over different chromosomes. 22. 24. and give an example of epigenetic changes discussed in the text or in class. gene. and DNA. transcription initiation complex. Heterochromatin is highly condensed and rarely expressed. and how is it maintained? Give an example discussed earlier in human genetics. EXPLANATION 28. What is the result of this methylation? 25. Gene expression can be regulated by modifications of the chromatin. transcription factors. What is a plausible mechanism for the coordination of gene expression? 3 . Label the following elements: TATA box. An article in Scientific American about proteasomes was entitled “Little Chamber of Horrors. these RNAs are called noncoding RNAs. One of the noncoding RNAs that regulate gene expression is microRNA. Explain the two modes of action of microRNAs. and give a specific example of when this might occur. How can proteins be activated. What is this role? 36. How can alternative RNA splicing result in different proteins derived from the same initial RNA transcript? 31. Posttranscriptional control includes regulation of mRNA degradation. Explain how this affects translation. processed. On the sketch below. Concept 18. Then explain their role in regulation of gene expression. called a “hairpin. 33. 34. Be sure to label the location of hydrogen bonds and Dicer.30. follow an RNA loop.3 Noncoding RNAs play multiple roles in controlling gene expression 35. 4 .” Explain how proteins are targeted for degradation. 32. It is now known that much of the RNA that is transcribed is not translated into protein. Read carefully to discern a crucial role played by these RNAs. and degraded? Give an example or describe each process. How do these “little chambers of horrors” function? Annotate the sketch below to describe their action.” from its creation. 4 A program of differential gene expression leads to the different cell types in a multicellular organism This concept deals with the regulation of gene expression in development. Animal development is also discussed in Chapter 47.Concept 18. distribution of cytoplasmic determinants b. 41. What mechanism is involved in the beginning of tumor growth? Discuss oncogenes and protooncogenes. What is controlled by homeotic genes? Concept 18. What three processes lead to the transformation of a zygote into the organism? 38. Differential gene expression results from different activators in different cells. 44. What is meant by determination? Explain what this means within an embryonic cell. 39.5 Cancer results from genetic changes that affect cell cycle control 43. Explain what occurs in cell differentiation and morphogenesis. different inductive signals 40. What are three mechanisms for converting a proto-oncogene to an oncogene? 5 . 37. What process ensures that all the tissues and organs of an organism are in their characteristic places? Where do the molecular cues that control this process arise? 42. How do different sets of activators come to be present in two cells? Explain how each of these occurs: a. Tumor-suppressor genes help prevent uncontrolled cell growth.________ 5.________ 6.________ 9. Explain the multistep model of cancer development by using the specific example of colorectal cancer.” Describe the double whammy that results from mutation of p53. which codes for a G protein and is an oncogene. 47. The figure below may be labeled to help in your explanation._______ 2.________ 4. Label the sketch below to explain how a ras mutation leads to cancer. which code for proteins to regulate cell growth. Place your answers here: 1. Testing Your Understanding: Self-Quiz Answers Now you should be ready to test your knowledge. and should not be stuck “on. 46. So important is the p53 gene that it is sometimes called the “guardian angel of the genome.________ 6 .________ 7.________ 8._______ 3. and tumorsuppressor genes. which work like the brakes on a car and must function! Let’s begin with a look at the ras gene.” much like the accelerator in a car.________ 10.45. There seem to be two categories of genes involved in cancer: oncogenes. One that is found mutated (and therefore nonfunctional) in more than 50% of human cancer is p53.