24.5. Lesson 24.5 Nucleic Acids. Overview. In this lesson, you will cover the topics of DNA replication, gene mutation, and DNA technologies.

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1 24.5 Lesson 24.5 Nucleic Acids Objectives Identify the functions of DNA and RNA Identify the number of bases of DNA required to specify one amino acid in a peptide chain Explain gene mutations Identify two examples of DNA technology used today. Lesson Links Ch. 24 Core TR: Section 5 Review Chapter 24 Online Student Edition 24.5 Lesson Overview (PowerPoint file) Study WB Chapter 24 Lesson 5 Overview/Materials Overview In this lesson, you will cover the topics of DNA replication, gene mutation, and DNA technologies. Standard 1 Block 0.5 Standard There are no items. Chemistry & You Engage Point out that some physical traits are inherited, while others are acquired during life. Ask What are some inherited traits? (hair color, eye color, blood type) Ask What are some acquired traits? ( muscle mass, hair length, skills) Activate Prior Knowledge page 1 of 7

2 Engage Have students call out all possible threeletter arrangements of A, B, and C (allow double and triple letters as in AAA, AAB, and so on), and list the arrangements on the board. (There should be 27 possible arrangements.) Tell students that the body uses nucleic acids in a similar fashion to code for amino acid sequences in proteins. DNA and RNA Explain Survey the class to see what they may know about DNA and RNA. Supplement as needed. Have them answer the following prompt in their notebooks. Figure 24.17_part1 Figure 24.17_part2 Figure 24.18_part1 Ask What are the basic characteristics of nucleic acids? (There are five naturally occurring nucleic acids, each with a phosphate, a sugar, and a nitrogen base. The sugar in RNA is ribose; the sugar in DNA is deoxyribose. The five bases are adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). Both RNA and DNA contain adenine, guanine, and cytosine. DNA also contains thymine; RNA contains uracil in place of thymine. The DNA helix is formed from two complementary strands of DNA, in which A bonds with T and C bonds with G.) Have students examine Figure 24.17_part1 and Figure 24.17_part2. Point out the sequence complementarity between strands. Ask How does the experimental data that moles A = moles T, and moles G = moles C support the concept of base pairing? (A and G are always hydrogen-bonded to T and C, respectively, in the opposite strand. Thus there is a one-to-one mole correspondence.) Then direct students' attention to the molecular structures in Figure 24.18_part1. Ask What features of the structure of the bases make this arrangement the best fit? ( Two hydrogen bonds in the T-A connection, three for C-G, and length of bonds.) page 2 of 7

3 Quick Lab Purpose To construct a model of double-stranded DNA Materials cardboard tube from paper-towel roll, two colors of markers, metric ruler, thumbtack, 10 toothpicks Prep Time 10 minutes Class Time 20 minutes Expected Outcome Models should have an orderly column of bases on the inside, with phosphate and sugar groups on the outside. Ask What forces hold the two strands of DNA together? (Primarily hydrogen bonding; dispersion forces also act between stacked bases.) Ask What forces the two strands apart? ( Repulsion of negative charges on phosphate groups; two strands have greater entropy than a single helical structure.) For Enrichment Ask What must occur to replicate base pairs of DNA? (The two strands must separate.) Instruct students to alter their model so that it can be used to demonstrate DNA replication. The Genetic Code Explain Table 24.2 Describe how a gene is a segment of DNA that carries the instructions for making one peptide chain. Display a copy of the Morse code. Point page 3 of 7

4 out that Morse code is a relatively simple human invention that uses arbitrary combinations of dots and dashes to represent letters of the alphabet. Tell students that the millions of possible sequences from the combination of only four nucleotides can be compared to the very large number of words that are formed from only two symbols the dot and dash of Morse code. Moreover, both systems use patterns to communicate information. The genetic code is a complex natural communication system that directs and controls all life processes. Make clear to students that while Morse code combinations vary from one to five symbols, all the base sequences in the genetic code are exactly three bases in length. Direct students' attention to Table Ask How many three-letter codes are there? (64) Ask Are all possible combinations of bases used? (yes) Ask Why are there more codes than amino acids? (Some amino acids have more than one code.) Ask Is there an advantage to redundant codes? (Redundancy might protect against harmful mutations.) Gene Mutations Explore Table 24.2 Have students practice reading the genetic code. Write a number of short DNA sequences on the board and ask students to use Table 24.2 to translate the genetic information into an amino-acid sequence. ( Example: A-C-G-G-C-A-A-G-A-G-A-A-T-G- G-A-C-T Cys-Arg-Ser-Leu-Thr-End) Then, ask students to predict the effects of substitutions, additions, and deletions on the translation of the DNA sequence. Emphasize that the mutation could be harmful or beneficial, but that it will lead to a different end product than was initially determined. Ask How might this sequence be affected if a thymine were substituted for the first guanine? (This mutation would insert a stop code. The protein synthesis would prematurely terminate and there would most likely be no biological activity.) page 4 of 7

5 Gene Mutations Extend Have students research two common gene mutations and two rare gene mutations and the effects of each in humans or animals. Encourage students to determine if the mutations resulted from a substitution, addition, or deletion of one or more nucleotides. DNA Technologies Explain Describe how DNA typing is used to identify a person from samples of their personal DNA because DNA sequences are unique for each individual. Tell students that DNA fingerprinting has been controversial in terms of its reliability. Explain to the class that the closer the match between two samples of DNA, the more likely that the two samples are from one individual. Tell students that one of the reasons people are nervous about the reliability of DNA results is that the expense of scanning evidence increases with each region of DNA that is scanned. Explain that the reliability of DNA fingerprinting varies, depending on the number of regions scanned and the level of expertise of the interpreter. Ask What current events or past criminal trials have you read about that involve the reliability of DNA fingerprinting? (Answers will vary.) Ask Do you think that proven scientific discoveries should be allowed to exonerate people in jail for crimes that were judged using evidence examination techniques from the past? (Generate a class discussion using a well-known criminal trial.) Ask If you were on a jury, which would you think is more reliable: an eyewitness or the results of DNA fingerprinting? (Answers may vary, but inform students that the reliability of an eyewitness is 50:50) page 5 of 7

6 Describe recombinant DNA technology and how it is used to insert a new piece of DNA into a pre-existing strand. Explain that it can be used in medicine and agriculture and describe several specific applications. Point out that the treatment of human diseases with recombinant proteins, though effective, is a replacement therapy. Explain that patients must have a continuous supply of the protein to remain asymptomatic. Ultimately, genetic engineers would like to develop methods for treating the cause of a genetically linked disorder by enabling the patient's own cells to produce a missing or faulty protein, an area of research referred to as gene therapy. Assess and Remediate Evaluate Have students write a short paragraph comparing and contrasting DNA and RNA and explaining their roles in the production of proteins. Chapter 24 Online Student Edition Figure 24.17_part1 Figure 24.17_part2 Then, have the students complete the 24.5 Lesson Check. Remediate Display Figure 24.17_part1 and Figure 24.17_part2. Use it to review the chemical and functional differences between DNA and RNA. Have students identify a complementary RNA strand for one of the strands of DNA shown in the figure. Differentiated Instruction Struggling Students Review the difference between hydrogen bonding and chemical bonding. Reinforce the concept that DNA strands are held together by hydrogen bonds rather than as a result of chemical reactions. Less Proficient Readers Table 24.1 Table 24.2 Ch. 24 Core TR: Section 5 Review Study WB Chapter 24 Lesson 5 Provide students with a copy of Table 24.1 so they can know what amino acids the page 6 of 7

7 abbreviations in Table 24.2 represent. Help students interpret the information present in both tables. Advanced Students Challenge students to write a computer program that converts any sequence of DNA bases into an amino-acid sequence by using the three-letter codes in Table Focus on ELL Frontload the Lesson As a class, discuss the shortcuts students use when texting, instant messaging, or ing, such as LOL, BRB, and BBS. Then tell students that, just as they use these three-letter codes to convey specific meanings in electronic conversation, DNA uses nucleic acids grouped in threes to code for specific amino acids. Ch. 24 Core TR: Section 5 Review Study WB Chapter 24 Lesson 5 My Notes Homework page 7 of 7