How Does a Plant Remember Winter Part 3

CASE STUDY WRAP-UP How does a plant remember The environment can exert long-term influences on gene expression by triggering epigenetic changes in DNA. Flowering in winter wheat is regulated by just such changes. Cancer cells (yellow) (SEM 2400x) Technology on the Case Epigenetics and Cancer Careers on the Case Work Toward a Solution The study of epigenetics is being applied in some unexpected ways, such as nutrition. Nutritionist To help people eat healthful diets, nutritionists study the nutrients in foods and the way they affect the body. Nutritionists may work in hospitals or doctor’s offices, or work for companies that manufacture foods.  VIDEO Watch this video to learn about other careers in biology. What causes cancer? For many years, scientists thought that the main cause was damage to DNA. Chemicals in tobacco cause this type of damage, which is why tobacco users have a high risk for cancer. However, new research shows that epigenetic mechanisms can also play a role in causing cancer. For example, some genes act to regulate the growth of the cell. If an epigenetic change “turns off” these genes, then cell growth will keep going unchecked and lead to a cancerous tumor. Another example involves the genes that help repair DNA. If these genes become deactivated, then cancer could be theresult. The good news is that epigenetic changes sometimes can be reversed. Researchers are investigating several epigenetic treatments for cancer, and the results have been encouraging. The goal of epigenetic therapy is not to kill the cancer cells, which is the goal of conventional treatments for cancer. Instead, epigenetic therapy works by reactivating the genes that help the body fight cancer naturally. Scientists are also applying epigenetics to help explain some cancer statistics. For example, research shows that people who regularly take aspirin are less likely to get certain types of cancer. The reason might be that aspirin reduces inflammation within cells. If the inflammation affects DNA in the cell nucleus, then epigenetic changes could be the result. CHAPTER 14 STUDY GUIDE Lesson Review Go to your Biology Foundations Workbook for longer versions of these lesson summaries. 14.1 RNA Unlike DNA, RNA uses the sugar ribose instead of deoxyribose, RNA is generally single stranded, and RNA contains uracil in place of thymine. There are three main types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). In transcription, segments of DNA serve as templates to produce complementary RNA molecules. • RNA • messenger RNA • ribosomal RNA • transfer RNA • transcription RNA Ribonucleic Acid • RNA polymerase • promoter • intron • exon DNA Deoxyribonucleic Acid 14.2 Ribosomes and Protein Synthesis The genetic code is a language composed of the four different bases of RNA: adenine, cytosine, guanine, and uracil. The code is read three letters at a time to carry instructions for the 20 different amino acids commonly found in polypeptides. Each threeletter combination in mRNA is a codon. Because there are four different bases, there are 64 possible three-base codons in the genetic code. The order in which amino acids are joined together in a peptide determines the shape, the chemical properties, and ultimately the function of the protein. In the cell, ribosomes use the sequence of codons in mRNA to assemble amino acids into polypeptide chains in a process called translation. All three major forms of RNA are involved in the process of translation. After the genetic code was discovered, the new field of molecular biology was established. Molecular biologists seek to understand the links between genes and the characteristics they influence. ine U U e rin Se UC A G  Compare and Contrast What are the differences between RNA and DNA? • translation • anticodon Leuc Phenylalanine • polypeptide • genetic code • codon U C C A e in os r Ty G U C A G p Sto A G eine U Cyst C Stop A G Tryptophan  Interpret Diagrams Which amino acid is specified by the codon UAC? 14.3 Gene Regulation and Expression DNA-binding proteins in prokaryotes regulate genes by controlling transcription. By binding DNA sequences in the regulatory regions of eukaryotic genes, transcription factors control gene expression. Master control genes are like switches that trigger particular patterns of development and differentiation in cells and tissues. • operon • operator • differentiation • homeotic gene • homeobox gene • Hox gene 14.4 Mutations Mutations can involve changes in the sequence of nucleotides in DNA. They can also involve changes in the number or structure of chromosomes in an organism. A change in a single base pair is known as a point mutation. The insertion or deletion of one or many bases in DNA is called a frameshift mutation. These mutations shift the “reading frame” of the genetic message. Chromosomal mutations involve changes in the number or structure of chromosomes and include deletion, duplication, inversion, and translocation. Some mutations arise from mutagens, which interact with DNA to produce cell damage. The most harmful mutations dramatically change protein structure or gene activity, producing genetic disorders, such as cancer. • mutation • point mutation • frameshift mutation • mutagen • polyploidy Deletion  Apply Concepts What is a genetic explanation for the difference in these two Himalayan rabbits? G T A C C A T G G A A T .. A U G U U A .. Met G U A C C Val Pro ?  Cause and Effect How does the deletion of a single base cause a frameshift mutation? Organize Information Complete the table to describe the molecules involved in protein synthesis. One entry is completed for you. Molecule Function mRNA 1. rRNA 2. tRNA Binds amino acids, brings them to the ribosomes, and reads the mRNA codons by base pairing Introns and exons 3. Transcription factors 4. PERFORMANCE-BASED ASSESSMENT A New Kind ofDrug: mRNA Evaluate a Solution STEM What happens when you take a conventional drug, such as aspirin or penicillin? The drug travels through the blood stream, and then is absorbed by body cells or (aswith penicillin) by the cells of bacteria or other invaders. The drug does its work, but eventually it goes away. Enzymes and other mechanisms break apart drugs and remove them from thebody. Today, researchers are trying to develop drugs in a very different way. The new drugs are a modified form of messenger RNA (mRNA). Instead of directly completing the tasks of the drug, the modified mRNA enters the cell and directs protein synthesis. Then the protein takes action as a drug or medicine. The protein might be a vaccine or antibody, or it might be an enzyme that the body cannot make or that it needs in an increased supply. To develop mRNA drugs, researchers had to find a way to make the molecules last longer in the body than they generally do. They also needed to “trick” the target cell into recognizing and accepting the drug. Otherwise, the cell might attack the drug as if it were a virus. Researchers met both challenges with the same solution. The drug is not quite the same as the natural mRNA found in cells. Instead, it uses a few nucleotides that are slightly different from the normal nucleotides found in RNA. The modifications make the mRNA both more stable and less viruslike. The process of RNA therapy can be summarized as follows: 1 Modified mRNA is synthesized in a laboratory cell culture. 2 The mRNA is delivered into the patient. Often it is injected with a vector, or carrier, such as a deactivated virus. 3 Inside cells, the mRNA attaches to ribosomes, as if it were the natural mRNA of the cell. 4 The mRNA directs protein synthesis. 5 The protein fills a positive role in the body, just like a conventional drug or medicine. SCIENCE PROJECT 1. Form a Hypothesis Would this therapy work if mRNA were replaced with other types of RNA, such as ribosomal RNA (rRNA) or transfer RNA (tRNA)? Use evidence to support your hypothesis. 2. Evaluate a Solution What are the advantages of using mRNA, rather than DNA, for directing the synthesis of the drug? (HINT: Remember the role of regulating gene expression in thecell.) 3. Develop Models Review the steps of administering an mRNA drug. Add illustrations to the figure to model the processes that are occuring inside the cell with the mRNA drug. Either draw the illustrations by hand or copy diagrams from thechapter. 4. Use Models Use your model to compare the administration of an mRNA drug to the protein synthesis that the cell normally performs. 5. Conduct Research Use an online search engine to research more information about mRNA drugs, their uses, and their development. Be sure to take notes and to cite your sources. 6. Communicate Information Share your findings about mRNA drugs in an oral report to the class, or in a written essay or computer presentation. Address these questions: • Why are companies investing in mRNA drugs? • What advances in technology have allowed mRNA drugs to be developed? • What kinds of proteins can mRNA drugs be used to synthesize? CHAPTER 14  ASSESSMENT KEY QUESTIONS AND TERMS 14.1 RNA HS-LS1-1, HS-LS3-1 10. What are the four bases of the genetic code? 11. What is the difference between translation and transcription? 12. How is molecular biology related to genetics? 1. RNA differs from DNA in that RNA has a. a double strand and contains uracil. b. a single strand and contains adenine. c. a double strand and contains thymine. d. a single strand and contains uracil. 14.3 Gene Regulation and Expression 2. From which molecules are mRNA molecules transcribed? a. tRNA c. DNA b. rRNA d. protein 13. Gene regulation in eukaryotic cells a. usually involves operons. b. is simpler than in prokaryotes. c. allows for cell specialization. d. includes the action of an operator region. HS-LS3-1 3. Which of the following are found in both DNA and RNA? a. ribose, phosphate groups, and adenine b. deoxyribose, phosphate groups, and guanine c. phosphate groups, guanine, and cytosine d. phosphate groups, guanine, and thymine 14. What is a promoter? a. a binding site for DNA polymerase b. a binding site for RNA polymerase c. a start signal for replication d. a stop signal for transcription 4. What is the function of RNA polymerase in the process of transcription? 15. What happens to lac repressors in E. coli when lactose is present? 5. Identify the three types of RNA and describe their functions. 16. Explain the function of homeotic genes and Hox genes. 6. What are introns and exons? 17. Describe how a TATA box helps position RNA polymerase in a eukaryotic cell. 14.2 Ribosomes and Protein Synthesis HS-LS1-1, HS-LS3-1 7. What happens during translation? a. Messenger RNA is made from a DNA code. b. The cell uses a messenger RNA code to make proteins. c. Transfer RNA is made from a messenger RNA code. d. Copies of DNA molecules are made. 8. The genetic code is always read a. 3 bases at a time in the same direction. b. 4 bases at a time in the same direction. c. 3 bases at a time and the direction varies. d. 4 bases at a time and the direction varies. 9. Ribosomes are tiny “factories” within cells that do all of the following EXCEPT a. decode an mRNA message into a protein. b. assemble amino acids into polypeptide chains. c. attach to mRNA molecules in the cytoplasm. d. translate DNA into RNA. 14.4 Mutations HS-LS3-1, HS-LS3-2 18. What is the name for a mutation that involves one nucleotide only? a. mutagen b. inversion c. point mutation d. translocation 19. When a chromosome undergoes a deletion mutation, information is a. repeated. c. reversed. b. lost. d. transferred. 20. A substance such as tobacco that can cause a genetic change is called a(n) a. polyploidy. c. mutagen. b. antigen. d. collagen. 21. Which kind of mutation is shown below? A B A C C D B E D F E F 22. How can a mutation be beneficial to an organism? CRITICAL THINKING HS-LS1-1, HS-LS3-1, HS-LS3-2 Valine Arginine e Serin ine Lys A C U e A p Sto ne Cystei Stop Tryptophan U GA C C U G Pr Leucin e oli ne e 4 ine tam din sti e Arginin Meth s ro Ty C A G U C A G U C A G U C A G A U G G A U CU GA C U Hi C ine A G Glu Th reo nin e A C A C A G UC G U G A C U G U A C A G UC A G Se rin C G U U ine rag pa As C e U G A C U G A C U G G A C U ionin ine Isoleucine an ne Glyci ic tam Glu id ac rtic pa As cid a Al Phenylalanine Leuci ne Refer to the genetic code diagram below to answer questions 23–25. 23. Analyze Data Suppose you start with the DNA strand ACCGTCACT. What three amino acids does the complementary mRNA strand code for? 24. Construct a Table Construct a two-column table that presents the possible mRNA codons for the following amino acids: alanine, valine, and leucine. 25. Analyze Data Analyze the information in the table you constructed for question 24. How would a substitution mutation in the third nucleotide position of the codons for alanine and valine affect the resulting protein? 26. Defend Your Claim During what stage of meiosis will a failure of chromosomes to separate lead to polyploidy? Use evidence from the text to defend your claim. 27. Construct an Explanation Nitrous acid is a mutagen. It can react chemically with cytosine to change it to uracil in a DNA strand. Using your knowledge of DNA replication and base pairing, explain the effect of this mutagen on a strand of DNA that undergoes replication. 28. Evaluate Evidence In eukaryotes, the number of promoter sequences and enhancer sites and the TATA box make gene regulation far more complex than regulation in prokaryotes. Why is regulation in eukaryotes so much more complex? 29. Evaluate Claims A chromosomal mutation that occurs during meiosis may or may not be expressed in an organism’s offspring. A similar mutation that only occurs during mitosis of a body cell will not be expressed in the organism’s offspring. Evaluate these claims. Determine whether or not they are true, and explain your reasoning. 30. Form a Hypothesis E. coli bacteria need the amino acid tryptophan to survive. When tryptophan is present in its growth medium, E. coli is able to ingest it. However, tryptophan is not always available in the E. coli’s environment. What are some questions you can ask regarding how E.coli might respond if tryptophan were not present in its growth medium? Form a hypothesis that you can test to answer one of your questions. 31. Construct an Argument A researcher identifies the nucleotide sequence AAC in a long strand of RNA inside a nucleus. In the genetic code, AAC codes for the amino acid asparagine. When that RNA becomes involved in protein synthesis, will asparagine necessarily appear in the protein? Use specific content to support your argument. 32. Analyze A mutation in the DNA of an organism changes one base sequence in a protein-coding region from CAC to CAT. What is the effect of the mutation on the final protein? CHAPTER 14  ASSESSMENT CROSSCUTTING CONCEPTS LANGUAGE ARTS CONNECTION 33. Patterns The word transcribe means “to write out.” The word translate means “to express in another language.” Review the meanings of transcription and translation in genetics. Look for patterns in the meanings of these words. How do the technical meanings of these words relate to the everyday meanings of the words? Write About Science 34. Structure and Function Describe how the sequence of nucleotides in mRNA codes for the amino acids of a protein. How can the insertion or deletion of even one nucleotide in mRNA cause significant changes to the protein that results? 38. Write Arguments A classmate tells you that comic books are full of superheroes with powers caused by mutations. Therefore, all mutations must be beneficial. Decide whether or not you agree. Write a paragraph to argue your position regarding the benefits or harm caused by mutations. 39. Use Information Explain what Hox genes are and what they control. Incorporate paraphrasing from the text into your explanation. Read About Science MATH CONNECTIONS Analyze and Interpret Data CCSS.MATH.CONTENT.MP2 RNA is the genetic material of many viruses. Scientists analyzed RNA from four different types of viruses. The content of the four nitrogenous bases is shown below. Base Percentages in Four Viruses Virus A U C G A 26.3 29.3 20.6 23.8 B × × C 21.9 12.8 34.3 31.1 D 29.8 26.3 18.5 25.3 17.6 17.5 Use the data table to answer questions 35–37. 35. Interpret Tables Which of the four types of viruses is most likely to use double-stranded RNA as its genetic material? Explain how you reached your conclusion. 36. Calculate Based on the data, calculate the values in the two boxes labeled with an ×. 37. Reason Quantitatively How would the percentages of the four nitrogenous bases shown in the table compare to the percentages of the nitrogenous bases found in strands of DNA? 40. Corroborate Research several different examples of epigenetics. Based on your understanding of epigenetics, explain how the patterns of expression are similar and how they are different. CHAPTER 14 END-OF-COURSE TEST PRACTICE e Serin i Lys ne ine G C U A C ine e Se r in U C GA C U G Pr oli ne ne tam ine e Meth in os idi on r Ty p C Sto A G e U Cystein C Stop A G Tryptophan U C Leucine A G U C A G Glu G A U CU G AC U A A U G e G st Hi CU Arginin Th re A C A C ine G UC G U U g ara sp A G U C A A G U C AG e Arginine C U G A C U G A C U G A UC A ionin Valine G A U AG Isoleucine ine C ne an Leuc Glyci c r ti pa As acid ic tam Glu acid Al Phenylalanine Questions 1–2 refer to the following diagram. 1. What is the significance of this genetic code? A. It describes how DNA is transcribed to RNA. B. It describes how RNA is translated to amino acids. C. It describes how RNA is translated to genes. D. It describes how proteins are translated to RNA. E. It describes how RNA is translated to DNA. 2. Two scientists are both studying RNA. One scientist is studying RNA in mice, and the other is studying RNA in E. coli bacteria. Which of the following best describes how each scientist would use a genetic code? A. Both scientists would use the same genetic code because all organisms have RNA. B. Both scientists would use the same genetic code because in all organisms the code is read three bases at a time and in the same direction. C. The scientists would use different genetic codes because different genes are expressed in mice and E. coli. D. The scientist studying mice would use the genetic code for mice and the scientist studying E. coli would use the genetic code for E.coli because mice are more complex multicellular organisms. E. The scientist studying mice would use the genetic code for eukaryotes and the scientist studying E. coli would use the genetic code for prokaryotes because they each have different types of chromosomes. 3. Human nerve cells and muscle cells have many structural and functional differences. What role does DNA play in these differences? A. Nerve cells and muscle cells contain different DNA. B. Nerve cells contain more DNA than muscle cells. C. DNA in muscle cells is condensed into chromatids. D. Muscle cells are more likely to have DNA mutations than nerve cells. E. Transcription factors and gene expression is different in nerve cells and muscle cells.  ASSESSMENT For additional assessment practice, go online to access your digital course. If You Have Trouble With... Question 1 2 See Lesson Performance Expectation 14.2 14.2 HS-LS1-1 HS-LS1-1 3 14.3 HS-LS3-1