TE Molecular Genetics: From DNA to Proteins

TE Molecular Genetics: From

DNA to Proteins

Jean Brainard, Ph.D. (JBrainard)

CK12 Editor

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AUTHORS

Jean Brainard, Ph.D. (JBrainard)

CK12 Editor

EDITOR

Douglas

(DWilkin)

Wilkin, Ph.D.

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Chapter 1. TE Molecular Genetics: From DNA to Proteins

C HAPTER

1

TE Molecular Genetics:

From DNA to Proteins

C

HAPTER

O

UTLINE

1.1

1.2

DNA and RNA

Protein Synthesis

1.3

1.4

1.5

Mutation

Regulation of Gene Expression

Worksheet Answer Keys

(Opening image copyright by 4designerart, 2010. Used under license from Shutterstock.com.)

Molecular Genetics: From DNA to Proteins

Outline

Lesson 7.1: DNA and RNA

7.1.1 Central Dogma of Molecular Biology

7.1.2 DNA

• Griffith Searches for the Genetic Material

• Avery’s Team Makes a Major Contribution

• Hershey and Chase Seal the Deal

• Chargaff Writes the Rules

• The Double Helix

• DNA Replication

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7.1.3 RNA

• RNA vs. DNA

• Types of RNA

Lesson 7.2: Protein Synthesis

7.2.1 Transcription

• Steps of Transcription

• Processing mRNA

7.2.2 The Genetic Code

• Reading the Genetic Code

• Characteristics of the Genetic Code

7.2.3 Translation

Lesson 7.3: Mutation

7.3.1 Causes of Mutation

7.3.2 Types of Mutations

• Chromosomal Alterations

• Point Mutations

• Frameshift Mutations

7.3.3 Effects of Mutations

• Beneficial Mutations

• Harmful Mutations

Lesson 7.4: Regulation of Gene Expression

7.4.1 How Gene Expression Is Regulated

7.4.2 Prokaryotic Gene Regulation

• The Role of Operons

• The Lac Operon

7.4.3 Eukaryotic Gene Regulation

• The TATA Box

• Regulation During Development

• Gene Regulation and Cancer

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Pacing the Lessons

Use the Class Periods per Lesson table below as a guide for the time required to teach the lessons of this chapter.

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Lesson

7.1

DNA and RNA

7.2

Protein Synthesis

7.3

Mutation

7.4

Regulation of Gene Expression

• Class periods are assumed to be 60 minutes long.

T ABLE 1.1:

Number of Class Periods

1.5

2.0

1.0

1.0

Online Resources

The following labs are suitable for this chapter and are available online:

1. Students can extract their own DNA (from cheek cells) and learn about DNA structure and replication. (Lesson

7.1)

• http://serendip.brynmawr.edu/sci_edu/waldron/#dna

2. Students will use simple paper models to simulate DNA transcription and translation. (Lesson 7.2)

• http://serendip.brynmawr.edu/sci_edu/waldron/#dna

3. Groups of students will investigate a hypothetical anthrax case by modeling DNA sequencing. They will focus on the role of mutations in the identification of DNA samples. The lab uses online videos and animations. (Lessons

7.1 and 7.3)

• http://www.pbs.org/wgbh/nova/teachers/activities/0401_02_nsn.html

4. Students will transcribe and translate a DNA sequence containing a mutation. Then they will perform a BLAST search to determine the protein that is encoded in the sequence. They will also infer which disease is caused by the protein. (Lessons 7.1, 7.2, 7.3)

• http://teacherknowledge.wikispaces.com/Quist+-+Connecting+DNA+to+Disease+Using+BLAST

5. In this wet lab, students will investigate how genes are regulated during development by observing differential gene expression in genetically modified plants. The Web site provides extensive pre- and post-lab materials, worksheets, links, and other resources. The lab is suitable for AP biology students. (Lesson 7.4)

• http://www.moreheadplanetarium.org/files/Same_Genes_Notebook.pdf

These Web sites may also be helpful:

1. This Web page provides many relevant links for activities, articles, online animations, quizzes, and other materials on molecular genetics.

• http://www.nclark.net/DNA_RNA

2. This Web site from the Cold Spring Harbor Laboratory provides animations, photographs, biographical sketches, problems, and links for students to learn about and explore the molecules of genetics.

• http://www.dnaftb.org/dnaftb/

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1.1

DNA and RNA


Key Concept

The central dogma of molecular biology can be summed up as DNA → RNA → Protein. Starting in the early 1900s, several researchers made important discoveries about DNA and how it codes for proteins. Three types of RNA are also involved in protein synthesis: mRNA, rRNA, and tRNA.

Standards

• CA.9–12.IE.1.d, k; CA.9–12.LS.1.d; CA.9–12.LS.4.a; CA.9–12.LS.5.a

• NSES.9–12.A.1.6; NSES.9–12.A.2.1, 2, 5; NSES.9–12.C.1.1, 3; NSES.9–12.C.2.1; NSES.9–12.G.1.1; NSES.9–12.G.3.2,

3, 4

• AAAS.9–12.1.A.2; AAAS.9–12.5.B.3; AAAS.9–12.5.C.4

• McREL.9–12.11.3.1, 2, 3; McREL.9–12.11.4.1, 2; McREL.9–12.12.5.2, 3, 4; McREL.9–12.12.6.3, 4; McREL.9–12.13.2.1,

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Lesson Objectives

• State the central dogma of molecular biology.

• Outline discoveries that led to knowledge of DNA’s structure and function.

• Describe the structure of RNA, and identify the three main types of RNA.

Lesson Vocabulary

• central dogma of molecular biology : doctrine that genetic instructions in DNA are copied by RNA, which carries them to a ribosome where they are used to synthesize a protein (DNA → RNA → protein)

• Chargaff’s rules : observations by Erwin Chargaff that concentrations of the four nucleotide bases differ among species; and that, within a species, the concentrations of adenine and thymine are always about the same and the concentrations of cytosine and guanine are always about the same

• messenger RNA (mRNA) : type of RNA that copies genetic instructions from DNA in the nucleus and carries them to the cytoplasm

• ribosomal RNA (rRNA) : type of RNA that helps form ribosomes and assemble proteins

• transfer RNA (tRNA) : type of RNA that brings amino acids to ribosomes where they are joined together to form proteins

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Teaching Strategies

Introducing the Lesson

By taking the Tour of the Basics at the URL below, students can review genes and chromosomes and get an introduction to the structure of DNA.

• http://learn.genetics.utah.edu/content/begin/tour/

Activity

Have students build an edible model of DNA. This will help them learn the structure of DNA and how DNA bases pair. The URL below provides everything you and your students need for the activity.

• http://www.nclark.net/Have_Your_DNA_and_Eat_It_Too.pdf

Differentiated Instruction

Pair less proficient readers with more proficient readers, and ask pairs to make a table comparing and contrasting the structure and function of DNA and RNA. A sample table is shown below ( Table

1.2

).

LPR

T ABLE 1.2: RNA vs. DNA

Structure:

Bases:

Sugar:

Size:

Location:

RNA single stranded

C, G, A, U ribose relatively small nucleus and cytoplasm

DNA double stranded

C, G, A, T deoxyribose very large nucleus only

Enrichment

Ask your advanced students to do the online genetics tutorial at the URL below. It uses multimedia to present principles of molecular genetics at a more sophisticated level than the text.

• http://morgan.rutgers.edu/MorganWebFrames/How_to_use/HTU_Frameset.html

Science Inquiry

Have small groups of students do the activity Where Do Genes Begin?

(see URL below). In the activity, students will build a simple model of DNA and use it to investigate Chargaff’s rules and DNA sequencing.

• http://www.nclark.net/Watson_Crick_Model.pdf

Overcoming Misconceptions

Common student misconceptions about DNA include:

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Chapter 1. TE Molecular Genetics: From DNA to Proteins a. DNA, genes, and chromosomes are interchangeable concepts.

b. DNA is the only genetic material in the genome.

c. Simple organisms such as bacteria do not have DNA.

d. All DNA sequences code for proteins.

Work with students to restate each misconception so it is true.

Reinforce and Review

Lesson Worksheets

Copy and distribute the lesson worksheets in the CK-12 Biology Workbook . Ask students to complete the worksheets alone or in pairs as a review of lesson content.

Review Questions

Have students answer the Review Questions that are listed at the end of the lesson in their FlexBook.

• Sample answers to these questions will be provided upon request. Please send an email to teachersrequests@ck12.org to request sample answers.

Points to Consider

All three types of RNA are needed by cells to make proteins.

• Can you develop a model in which the three types of RNA interact to make a protein?

– (Try to elicit a range of responses.)

• How do you think mRNA copies the genetic instructions in DNA? How are these instructions encoded in the

DNA molecule?

– ( Sample answer: I think mRNA has a complementary sequence of bases to the DNA it copies and that the sequence of bases encodes the instructions.)

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1.2. Protein Synthesis

1.2

Protein Synthesis

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Key Concept

Transcription is the DNA → RNA part of the central dogma. It occurs in the nucleus. A copy of mRNA is made that is complementary to a strand of DNA. The sequence of bases in DNA or RNA makes up the genetic code, which is universal, unambiguous, and redundant. Translation is the RNA → protein part of the central dogma. It occurs at a ribosome. All three types of RNA are involved in translation.

Standards

• CA.9–12.IE.1.d; CA.9–12.LS.1.d; CA.9–12.LS.4.a, b, e; CA.9–12.LS.5.a, b

• NSES.9–12.A.1.6; NSES.9–12.C.1.1, 2, 3; NSES.9–12.C.2.1

• AAAS.9–12.5.B.3; AAAS.9–12.5.C.4


• Give an overview of transcription.

• Describe the genetic code.

• Explain how translation occurs.


• codon : group of three nitrogen bases in nucleic acids that makes up a code “word” of the genetic code and stands for an amino acid, start, or stop

• genetic code : universal code of three-base codons that encodes the genetic instructions for the amino acid sequence of proteins

• promoter : region of a gene where a RNA polymerase binds to initiate transcription of the gene

• protein synthesis : process in which cells make proteins that includes transcription of DNA and translation of mRNA

• transcription : process in which genetic instructions in DNA are copied to form a complementary strand of mRNA

• translation : process in which genetic instructions in mRNA are “read” to synthesize a protein

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Introduce protein synthesis by discussing the common meanings of transcription (copying words) and translation

(changing words from one language into another). Tell students they will read in this lesson how DNA is transcribed into RNA, which is then translated into a protein.

Activity

Divide the class into small groups and have each group do the activities RNA Transcription and RNA Translation , which can be accessed at the URL below. Students will develop a model that shows how the sequence of bases in

DNA determines the order of bases in mRNA. Then they will determine the amino acid sequence encoded in the mRNA.

• http://serendip.brynmawr.edu/sci_edu/waldron/pdf/DNATeachPrep.doc


Pair English language learners with native English speakers, and ask pairs to create a flow chart of protein synthesis, including both transcription and translation. Tell partners to sketch simple diagrams to illustrate the steps of the flow chart. Give them a chance to share their flow charts with the class.

ELL

Enrichment

Provide students with materials such as white yarn or string, colored markers, scissors, and clear tape. Then challenge the students to devise a way to use the materials to demonstrate RNA splicing. Set aside time for the students to present their demonstration to the class.

Science Inquiry

Assign the activity How Does DNA Determine the Traits of an Organism?

(see URL below). Students will analyze

DNA data for a fictitious organism named a snork. Then, based on the DNA base sequence, they will determine the organism’s traits. This fun activity can be done as a homework assignment.

• http://www.biologycorner.com/worksheets/snorks.html


A persistent misconception about protein synthesis is that amino acids are products, rather than reactants, of translation. Make sure students know that amino acids come from ingestion and biosynthesis, which are separate from translation.

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When DNA is replicated or transcribed, accidents can happen, leading to a change in the base sequence.

• What do you think could cause such accidents to occur?

– (Students might mention mutagens such as UV light.)

• How might the changes affect the reading frame? How might the encoded protein be affected?

– ( Sample answer: It might interrupt the reading frame. If that happened, the protein might be drastically affected.)

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1.3

Mutation


Key Concept

Mutations are caused by environmental factors known as mutagens. Examples of mutagens include radiation and certain chemicals. Germline mutations occur in gametes, and somatic mutations occur in other body cells. Mutations may alter entire chromosomes or change a single nucleotide. Their effects may be neutral, beneficial, or harmful.

Mutations are essential for evolution because they are the ultimate source of genetic variation in a species.

Standards

• CA.9–12.IE.4.c; CA.9–12.LS.7.c

• NSES.9–12.C.2.3; NSES.9–12.C.3.1; NSES.9–12.F.1.1

• AAAS.9–12.5.A.1; AAAS.9–12.5.B.4, 5; AAAS.9–12.5.C.6; AAAS.9–12.5.F.3, 5; AAAS.9–12.6.E.2


• Identify causes of mutation.

• Compare and contrast types of mutations.

• Explain how mutations may affect the organisms in which they occur.


• chromosomal alteration : mutation that changes chromosome structure

• frameshift mutation : deletion or insertion of one or more nucleotides that changes the reading frame of the genetic material

• genetic disorder : disease caused by a mutation in one or a few genes

• germline mutation : mutation that occur in gametes

• mutagen : environmental factor that causes mutations

• mutation : change in the sequence of bases in DNA or RNA

• point mutation : change in a single nucleotide base in the genetic material

• somatic mutation : mutation that occurs in cells of the body other than gametes

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Call on volunteers to describe drastic mutations they have read about or seen in science fiction stories or movies, or describe examples yourself. Explain that real mutations rarely have such drastic effects, but they are extremely important. Without them, evolution could not occur. Tell students they will learn more about mutations in this lesson.

Activity

Assign the activities at the URLs below. Students will investigate the effects of different mutations on the encoded proteins.

• http://serendip.brynmawr.edu/sci_edu/waldron/pdf/DNATeachPrep.doc

• http://molo.concord.org/database/activities/102.html


Pair less proficient readers with more proficient readers, and ask partners to make a table comparing and contrasting the following types of mutations: deletions, insertions, duplications, inversions, translocations, and point mutations.

LPR

Enrichment

Ask a group of students to create a public service announcement identifying common mutagens that may cause cancer and ways that people can reduce their exposure to them. Have students make a video of their announcement and present it to the class or, if possible, the entire school.

Science Inquiry

Have students do the online activity Test Neurofibromin Activity in a Cell (see URL below). After reading about the protein neurofibromin and its role in normal cell division, students will predict how mutations in the gene for this protein might affect cell division. Then they will use an interactive animation to test their prediction. They will observe the simulated effects of different mutations on cells as though seen through a microscope.

• http://learn.genetics.utah.edu/content/begin/dna/neurofibromin/


Misconceptions about mutations are common. Discuss the examples below and give students the correct facts as well as examples of mutations that illustrate why the misconceptions are false.

1. All mutations are harmful.

• Fact: Most mutations are neutral and some may even be beneficial. For several examples of beneficial mutations in yeast and bacteria, go to this link:

– http://www.gate.net/ rwms/EvoMutations.html

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2. All mutations change the protein products of genes.

• Fact: Some mutations have no effect on protein products. For example, mutations may occur in noncoding sections of DNA, or they may result in synonymous codons that code for the same amino acids.

3. All mutations have phenotypic effects.

• Fact: Many mutations are recessive and do not affect phenotypes. Having one copy of the normal allele is sufficient for a normal phenotype. For example, the mutations that cause PKU and cystic fibrosis are recessive.

Two copies of the recessive alleles must be present for the diseases to appear in the phenotype.








Sometimes even drastic mutations do not affect the proteins produced by a particular type of cell. The reason? The genes affected by the mutations are not normally used to make proteins in that type of cell. In all cells, some genes are turned off — they are not transcribed — while other genes are turned on.

• How do cells control which genes are turned on and used to make proteins?

– (Students might say cells have special genes that control which other genes are turned on.)

• Can you think of a mechanism that might prevent transcription of a gene?

– (Encourage creative but reasonable responses.)

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1.4. Regulation of Gene Expression

1.4

Regulation of Gene Expression

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Key Concept

Gene transcription is controlled by regulatory elements on DNA that either activate or repress transcription. In prokaryotes, this typically involves an operon, such as the lac operon in E. coli . In eukaryotes, regulation of transcription is more complex. It generally includes regulatory elements such as the TATA box and homeobox genes that switch other regulatory genes on or off.

Standards

• CA.9–12.IE.1.d; CA.9–12.LS.4.d

• NSES.9–12.A.1.6; NSES.9–12.C.1.4, 6

• AAAS.9–12.5.B.6; AAAS.9–12.5.C.6; AAAS.9–12.6.B.1


• Identify general mechanisms that regulate gene expression.

• Describe how gene regulation occurs in prokaryotes.

• Give an overview of gene regulation in eukaryotes.


• gene expression : use of a gene to make a protein

• homeobox gene : gene that codes for regulatory proteins that control gene expression during development

• operator : a region of an operon where regulatory proteins bind

• operon : region of prokaryotic DNA that consists of a promoter, an operator, and one or more genes that encode proteins needed for a specific function

• regulatory element : region of DNA where a regulatory protein binds

• regulatory protein : protein that regulates gene expression

• TATA box : regulatory element that is part of the promoter of most eukaryotic genes

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Introduce gene regulation with an analogy. Tell students that the genes we inherit are like the hard drive of a computer, but each type of cell has its own separate “software.” The “software” turns on or off a particular set of genes through the mechanisms of gene regulation. Tell students they will learn how genes are regulated in this lesson.

Demonstration

Suggest that students watch the online animation below. It demonstrates the lac operon mechanism for gene regulation.

• http://www.dnatube.com/video/22/Lac-operon-mechanism


Pair less proficient readers with more proficient readers, and ask pairs to work together to make a main ideas/details chart for the lesson. Suggest that they try to write a main idea for each heading and subheading in the lesson and include at least one detail per main idea.

LPR

Enrichment

This lesson focuses on transcriptional regulation of gene expression. Have interested students research translational regulation. Ask them to summarize at least one translational regulation mechanism, such as microRNA-mediated regulation, and present their summary to the class. Encourage them to make a diagram to help explain the mechanism.

Science Inquiry

Challenge groups of students to formulate a hypothesis for how the lac operon evolved. They should consider why it might be advantageous for an organism to be able to control the production of proteins that it needs only in certain situations, rather than produce the proteins all the time. Give groups a chance to share and discuss their hypotheses.

Health Connection

Elaborate on the connection between gene regulation and cancer that is presented in the lesson. Explain that tumorsuppressor genes normally act like “brakes” to inhibit cell growth and division, whereas proto-oncogenes normally act like “gas pedals” to accelerate cell growth and division. When mutations occur in these genes, it’s similar to the cells to losing their brakes and hitting the gas pedal. The cells grow and divide uncontrollably. Students can learn more by watching the video at the URL below.

• http://www.youtube.com/watch?v=ZCy7gCPWEcM

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Scientists know more about human chromosomes and genes than they know about the genetic material of most other species. In fact, scientists have identified all of the approximately 20,000-25,000 genes in human DNA.

• What do you know about human chromosomes and genes? For example, do you know how many chromosomes humans normally have?

– (Humans normally have 23 pairs, or 46 chromosomes in each cell.)

• Do you know how human characteristics are inherited? Can you identify characteristics that are controlled by a single gene?

– ( Sample answers: Human characteristics are inherited according to Mendel’s laws. ABO blood type is a characteristic controlled by a single gene.)

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1.5

Worksheet Answer Keys

• The worksheet answer keys are available upon request. Please send an email to teachers-requests@ck12.org

to request the worksheet answer keys.

17

TE Molecular Genetics: From DNA to Proteins

TE Molecular Genetics: From

DNA to Proteins

Jean Brainard, Ph.D. (JBrainard)

CK12 Editor

Say Thanks to the Authors

Click http://www.ck12.org/saythanks

(No sign in required)

C HAPTER