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Ch 10 Notes for website
- 1. Chapter 10 Molecular Biologyof the Gene PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
- 2. Figure 10.0_1 Chapter 10:Big Ideas The Structure of the Genetic Material DNA Replication The Flow of Genetic Information from DNA to RNA to Protein The Genetics of Viruses and Bacteria
- 3. 10.1 SCIENTIFIC DISCOVERY:Experiments showed that DNA is the genetic material Until the 1940s, the case for proteins serving as the genetic material was stronger than the case for DNA. – Proteins are made from 20 different amino acids. – DNA was known to be made from just four kinds of nucleotides. Studies of bacteria and viruses – ushered in the field of molecular biology, the study of heredity at the molecular level, and – revealed the role of DNA in heredity. © 2012 Pearson Education, Inc.
- 4. 10.1 SCIENTIFIC DISCOVERY:Experiments showed that DNA is the genetic material In 1928, Frederick Griffith discovered that a “transforming factor” could be transferred into a bacterial cell. He found that – when he exposed heat-killed pathogenic bacteria to harmless bacteria, some harmless bacteria were converted to disease-causing bacteria and – the disease-causing characteristic was inherited by descendants of the transformed cells. © 2012 Pearson Education, Inc.
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- 6. 10.1 SCIENTIFIC DISCOVERY:Experiments showed that DNA is the genetic material In 1952, Alfred Hershey and Martha Chase used bacteriophages to show that DNA is the genetic material of T2, a virus that infects the bacterium Escherichia coli (E. coli). – Bacteriophages (or phages for short) are viruses that infect bacterial cells. – Phages were labeled with radioactive sulfur to detect proteins or radioactive phosphorus to detect DNA. – Bacteria were infected with either type of labeled phage to determine which substance was injected into cells and which remained outside the infected cell. © 2012 Pearson Education, Inc.
- 7. 10.1 SCIENTIFIC DISCOVERY:Experiments showed that DNA is the genetic material – The sulfur-labeled protein stayed with the phages outside the bacterial cell, while the phosphorus-labeled DNA was detected inside cells. – Cells with phosphorus-labeled DNA produced new bacteriophages with radioactivity in DNA but not in protein. Animation: Hershey-Chase Experiment © 2012 Pearson Education, Inc.
- 8.
- 9. Figure 10.1B Phage Empty protein shell Radioactive protein Bacterium Centrifuge Pellet 1 Batch2: Radioactive DNA labeled in green Phage DNA DNA Batch 1: Radioactive protein labeled in yellow The radioactivity is in the liquid. 2 3 4 Radioactive DNA Centrifuge Pellet The radioactivity is in the pellet.
- 10. 10.2 DNA andRNA are polymers of nucleotides DNA and RNA are nucleic acids. One of the two strands of DNA is a DNA polynucleotide, a nucleotide polymer (chain). A nucleotide is composed of a – nitrogenous base, – five-carbon sugar, and – phosphate group. The nucleotides are joined to one another by a sugar-phosphate backbone. © 2012 Pearson Education, Inc.
- 11. 10.2 DNA andRNA are polymers of nucleotides Each type of DNA nucleotide has a different nitrogen-containing base: – adenine (A), – cytosine (C), – thymine (T), and – guanine (G). © 2012 Pearson Education, Inc.
- 12. 10.2 DNA andRNA are Polymers of Nucleotides RNA (ribonucleic acid) is unlike DNA in that it – uses the sugar ribose (instead of deoxyribose in DNA) and – RNA has the nitrogenous base uracil (U) instead of thymine. © 2012 Pearson Education, Inc.
- 13. 10.3 SCIENTIFIC DISCOVERY:DNA is a double-stranded helix Watson and Crick reported that DNA consisted of two polynucleotide strands wrapped into a double helix. – The sugar-phosphate backbone is on the outside. – The nitrogenous bases are in the interior. – Specific pairs of bases give the helix a uniform shape. – A pairs with T, forming two hydrogen bonds, and – G pairs with C, forming three hydrogen bonds. © 2012 Pearson Education, Inc.
- 14. Figure 10.3D Hydrogen bond Basepair Ribbon model Partial chemical structure Computer model
- 15. 10.4 DNA replicationdepends on specific base pairing DNA replication follows a semiconservative model. – The two DNA strands separate. – Each strand is used as a pattern to produce a complementary strand, using specific base pairing. – Each new DNA helix has one old strand with one new strand. – DNA replication ensures that all the somatic cells in a multicellular organism carry the same genetic information. Animation: DNA Replication Overview © 2012 Pearson Education, Inc.
- 16. Figure 10.4A_s3 A T A C G C G C G A T A T A T A parental molecule ofDNA T A T A T A T C C A Free nucleotides The parental strands separate and serve as templates G C G C G C G G C G C T A T A T A T A T A Two identical daughter molecules of DNA are formed
- 17.
- 18. 10.5 DNA replicationproceeds in two directions at many sites simultaneously DNA replication begins at the origins of replication where – DNA unwinds at the origin to produce a “bubble,” – replication proceeds in both directions from the origin, and – replication ends when products from the bubbles merge with each other. © 2012 Pearson Education, Inc.
- 19.
- 20. 10.5 DNA replicationproceeds in two directions at many sites simultaneously DNA replication occurs in the 5′ to 3′ direction. – Replication is continuous on the 3′ to 5′ template. – Replication is discontinuous on the 5′ to 3′ template, forming short segments. © 2012 Pearson Education, Inc.
- 21. 10.5 DNA replicationproceeds in two directions at many sites simultaneously Two key proteins are involved in DNA replication. 1. DNA ligase joins small fragments into a continuous chain. 2. DNA polymerase – adds nucleotides to a growing chain and – proofreads and corrects improper base pairings. Animation: Origins of Replication Animation: Leading Strand Animation: Lagging Strand Animation: DNA Replication Review © 2012 Pearson Education, Inc.
- 22. Figure 10.5C DNA polymerase molecule 5′ 3′ ParentalDNA Replication fork 5′ 3′ DNA ligase Overall direction of replication 3′ 5′ This daughter strand is synthesized continuously This daughter strand is 3′ synthesized 5′ in pieces
- 23. 10.6 The DNAgenotype is expressed as proteins, which provide the molecular basis for phenotypic traits DNA specifies traits by dictating protein synthesis. The molecular chain of command is from – DNA in the nucleus to RNA and – RNA in the cytoplasm to protein. Transcription is the synthesis of RNA under the direction of DNA. Translation is the synthesis of proteins under the direction of RNA. © 2012 Pearson Education, Inc.
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- 25. 10.7 Genetic informationwritten in codons is translated into amino acid sequences The sequence of nucleotides in DNA provides a code for constructing a protein. – Protein construction requires a conversion of a nucleotide sequence to an amino acid sequence. – Transcription rewrites the DNA code into RNA, using the same nucleotide “language.” – Translation involves switching from the nucleotide “language” to the amino acid “language.” – Each amino acid is specified by a codon. – 64 codons are possible. – Some amino acids have more than one possible codon. © 2012 Pearson Education, Inc.
- 26. 10.9 Transcription producesgenetic messages in the form of RNA Overview of transcription – An RNA molecule is transcribed from a DNA template by a process that resembles the synthesis of a DNA strand during DNA replication. – RNA nucleotides are linked by the transcription enzyme RNA polymerase. – Specific sequences of nucleotides along the DNA mark where transcription begins and ends. – The “start transcribing” signal is a nucleotide sequence called a promoter. © 2012 Pearson Education, Inc.
- 27. Figure 10.8B_s3 DNA Strand tobe transcribed T A C T A T C T G A A G A A A A T C T T T T A G Transcription RNA A U G A A G U U U U A G Translation Start codon Polypeptide Met Stop codon Lys Phe
- 28. 10.9 Transcription producesgenetic messages in the form of RNA – Transcription begins with initiation, as the RNA polymerase attaches to the promoter. – During the second phase, elongation, the RNA grows longer. – As the RNA peels away, the DNA strands rejoin. – Finally, in the third phase, termination, the RNA polymerase reaches a sequence of bases in the DNA template called a terminator, which signals the end of the gene. – The polymerase molecule now detaches from the RNA molecule and the gene. Animation: Transcription © 2012 Pearson Education, Inc.
- 29. Figure 10.9A Free RNA nucleotides RNA polymerase A TC C A A T Direction of transcription Newly made RNA A T A G U G T C C A U C C A G T A G G T U T A C C Template strand of DNA
- 30. Figure 10.9B RNA polymerase DNAof gene Terminator DNA Promoter DNA 1 Initiation 2 Elongation 3 Termination Completed RNA Area shown in Figure 10.9A Growing RNA RNA polymerase
- 31. 10.10 Eukaryotic RNAis processed before leaving the nucleus as mRNA Messenger RNA (mRNA) – conveys genetic messages from DNA to the translation machinery of the cell – Eukaryotic mRNA has – introns, interrupting sequences that separate – exons, the coding regions. © 2012 Pearson Education, Inc.
- 32. 10.10 Eukaryotic RNAis processed before leaving the nucleus as mRNA Eukaryotic mRNA undergoes processing before leaving the nucleus. – RNA splicing removes introns and joins exons to produce a continuous coding sequence. – A cap and tail of extra nucleotides are added to the ends of the mRNA © 2012 Pearson Education, Inc.
- 33. Figure 10.10 Exon Intron Exon Intron Exon DNA Cap RNA transcript withcap and tail Transcription Addition of cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence NUCLEUS CYTOPLASM
- 34. 10.8 The geneticcode dictates how codons are translated into amino acids Characteristics of the genetic code – Three nucleotides specify one amino acid. – 61 codons correspond to amino acids. – AUG codes for methionine and signals the start of transcription. – 3 “stop” codons signal the end of translation. © 2012 Pearson Education, Inc.
- 35. Figure 10.8A Third base Firstbase Second base
- 36. 10.11 Transfer RNAmolecules serve as interpreters during translation Transfer RNA (tRNA) – converts the genetic message of mRNA into the language of proteins. Transfer RNA molecules pick up the appropriate amino acid using a special triplet of bases, called an anticodon, recognize the appropriate codons in the mRNA. Translation occurs on the surface of the ribosome. © 2012 Pearson Education, Inc.
- 37. Figure 10.12B tRNA bindingsites Large subunit P A site site Small subunit mRNA binding site
- 38. Figure 10.12C The nextamino acid to be added to the polypeptide Growing polypeptide mRNA tRNA Codons
- 39. 10.13 An initiationcodon marks the start of an mRNA message Translation can be divided into the same three phases as transcription: 1. initiation, 2. elongation, and 3. termination. © 2012 Pearson Education, Inc.
- 40. 10.13 An initiationcodon marks the start of an mRNA message Initiation establishes where translation will begin. Initiation occurs in two steps. 1. An mRNA molecule binds to a small ribosomal subunit and the first tRNA binds to mRNA at the start codon. – The start codon reads AUG and codes for methionine. – The first tRNA has the anticodon UAC. © 2012 Pearson Education, Inc.
- 41. Figure 10.13B Met Met Large ribosomal subunit Initiator tRNA P site mRNA U AC A U G Start codon 1 Small ribosomal subunit 2 U A C A U G A site
- 42. 10.14 Elongation addsamino acids to the polypeptide chain until a stop codon terminates translation Each cycle of elongation has three steps. 1. Codon recognition: The anticodon of an incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A site of the ribosome. 2. Peptide bond formation: The new amino acid is joined to the chain. 3. Translocation: tRNA is released from the P site and the ribosome moves tRNA from the A site into the P site. © 2012 Pearson Education, Inc.
- 43. 10.14 Elongation addsamino acids to the polypeptide chain until a stop codon terminates translation Elongation continues until the termination stage of translation, when – the ribosome reaches a stop codon, – the completed polypeptide is freed from the last tRNA, Animation: Translation © 2012 Pearson Education, Inc.
- 44.
- 45. Figure 10.15 Transcription DNA 1 mRNA Transcription RNA polymerase CYTOPLASM Translation Amino acid Aminoacid attachment 2 Enzyme tRNA ATP Anticodon Initiator tRNA Large ribosomal subunit Start Codon mRNA Initiation of polypeptide synthesis 3 Small ribosomal subunit New peptide bond forming Growing polypeptide 4 Elongation Codons mRNA Polypeptide 5 Stop codon Termination
- 46. 10.16 Mutations canchange the meaning of genes A mutation is any change in the nucleotide sequence of DNA. Mutations can involve – large chromosomal regions or – just a single nucleotide pair. © 2012 Pearson Education, Inc.
- 47. 10.16 Mutations canchange the meaning of genes Mutations within a gene can be divided into two general categories. 1. Base substitutions involve the replacement of one nucleotide with another. Base substitutions may – have no effect at all, producing a silent mutation, – change the amino acid coding, producing a missense mutation, which produces a different amino acid, – lead to a base substitution that produces an improved protein that enhances the success of the mutant organism and its descendant, or – change an amino acid into a stop codon, producing a nonsense mutation. © 2012 Pearson Education, Inc.
- 48. Figure 10.16A Normal hemoglobinDNA C T Mutant hemoglobin DNA C A T T mRNA mRNA G A A Normal hemoglobin Glu G U A Sickle-cell hemoglobin Val
- 49. 10.16 Mutations canchange the meaning of genes 2. Mutations can result in deletions or insertions that may – alter the reading frame (triplet grouping) of the mRNA, so that nucleotides are grouped into different codons, – lead to significant changes in amino acid sequence downstream of the mutation, and – produce a nonfunctional polypeptide. © 2012 Pearson Education, Inc.
- 50. 10.16 Mutations canchange the meaning of genes Mutations can be caused by – spontaneous errors that occur during DNA replication or recombination or – mutagens, which include – high-energy radiation such as X-rays and ultraviolet light and – chemicals. © 2012 Pearson Education, Inc.
- 51. Figure 10.16B Normal gene mRNA Protein Nucleotide substitution A U GA A G U Met A U G A Met U G G C G C Phe Lys U Gly Ala U A G C A G U U Lys Phe Ser G C A A Ala U Deleted Nucleotide deletion A U G A A G Met U U G G C G Ala Leu Lys C A U His Inserted Nucleotide insertion A U G A A G Met Lys U U G Leu U G G C G C Ala His
- 52. Viruses Viruses arenot generally considered alive because they – are not cellular and – cannot reproduce on their own. © 2012 Pearson Education, Inc.
- 53. 10.17 Viral DNAmay become part of the host chromosome A virus is essentially “genes in a box,” an infectious particle consisting of – a bit of nucleic acid, – wrapped in a protein coat called a capsid – Viruses have two types of reproductive cycles. 1. In the lytic cycle, – viral particles are produced using host cell components, – the host cell lyses, and – viruses are released. © 2012 Pearson Education, Inc.
- 54. 10.17 Viral DNAmay become part of the host chromosome 2. In the Lysogenic cycle – Viral DNA is inserted into the host chromosome by recombination. – Viral DNA is duplicated along with the host chromosome during each cell division. Animation: Phage Lambda Lysogenic and Lytic Cycles © 2012 Pearson Education, Inc.
- 55. Figure 10.17_1 Phage Attaches to cell PhageDNA cell lyses, releasing phages Bacterial chromosome 4 The 1 The phage injects its DNA Lytic cycle Phages assemble 2 3 New phage DNA and proteins are synthesized The phage DNA circularizes
- 56. Figure 10.17_2 Phage Attaches to cell PhageDNA Bacterial chromosome 1 The phage injects its DNA 7 Environmental stress Many cell divisions Lysogenic cycle 2 The phage DNA circularizes Prophage 6The lysogenic bacterium replicates normally, copying the prophage at each cell division 5 Phage DNA inserts into the bacterial chromosome by recombination
- 57. 10.19 EVOLUTION CONNECTION:Emerging viruses threaten human health Viruses that appear suddenly or are new to medical scientists are called emerging viruses. These include the – AIDS virus, – Ebola virus, – West Nile virus, and – SARS virus. © 2012 Pearson Education, Inc.
- 58. 10.19 EVOLUTION CONNECTION:Emerging viruses threaten human health Three processes contribute to the emergence of viral diseases: 1. mutation—RNA viruses mutate rapidly. 2. contact between species—viruses from other animals spread to humans. 3. spread from isolated human populations to larger human populations, often over great distances. © 2012 Pearson Education, Inc.
- 59. 10.22 Bacteria cantransfer DNA in three ways Bacteria are also valuable. – Bacterial DNA is found in a single, closed loop, chromosome. – Bacterial cells divide by replication of the bacterial chromosome and then by binary fission. – Because binary fission is an asexual process, bacteria in a colony are genetically identical to the parent cell. © 2012 Pearson Education, Inc.
- 60. Figure 10.22D Donated DNA Recipientcell’s chromosome Crossovers Degraded DNA Recombinant chromosome
- 61. You should nowbe able to 1. Describe the experiments of Griffith, Hershey, and Chase, which supported the idea that DNA was life’s genetic material. 2. Compare the structures of DNA and RNA. 3. Explain how the structure of DNA facilitates its replication. 4. Describe the process of DNA replication. 5. Describe the locations, reactants, and products of transcription and translation. 6. Explain how the “languages” of DNA and RNA are used to produce polypeptides. 7. Explain how mRNA is produced using DNA. 8. Explain how eukaryotic RNA is processed before leaving the nucleus. 9. Relate the structure of tRNA to its functions in the process of translation. 10. Describe the structure and function of ribosomes. 11. Describe the step-by-step process by which amino acids are added to a growing polypeptide chain. 12. Diagram the overall process of transcription and translation. 13. Describe the major types of mutations, causes of mutations, and potential consequences. 14. Compare the lytic and lysogenic reproductive cycles of a phage. 15. Describe three processes that contribute to the emergence of viral disease. 16. Define a plasmid © 2012 Pearson Education, Inc.
Editor's Notes
- #3 Figure 10.0_1 Chapter 10: Big Ideas
- #4 Student Misconceptions and Concerns 1. Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. 2. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10. Teaching Tips 1. A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. 2. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
- #5 Student Misconceptions and Concerns 1. Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. 2. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10. Teaching Tips 1. A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. 2. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
- #7 Student Misconceptions and Concerns 1. Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. 2. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10. Teaching Tips 1. A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. 2. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
- #8 Student Misconceptions and Concerns 1. Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. 2. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10. Teaching Tips 1. A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. 2. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
- #9 Figure 10.1A Phage T2
- #10 Figure 10.1B The Hershey-Chase experiment
- #11 Student Misconceptions and Concerns 1. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10. 2. Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips 1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). 2. Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars.
- #12 Student Misconceptions and Concerns 1. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10. 2. Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips 1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). 2. Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars.
- #13 Student Misconceptions and Concerns 1. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10. 2. Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips 1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). 2. Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars.
- #14 Student Misconceptions and Concerns Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips 1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). 2. The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to explain what the parts of the ladder represent. The wooden rungs represent pairs of nitrogenous bases joined by hydrogen bonds. Each rope represents a sugar-phosphate backbone.
- #15 Figure 10.3D Three representations of DNA
- #16 Student Misconceptions and Concerns The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips 1. Demonstrate the complementary base pairing within DNA. Present students with the base sequence to one side of a DNA molecule and have them work quickly at their seats to determine the sequence of the complimentary strand. For some students, these sorts of quick practice are necessary to reinforce a concept and break up a lecture. 2. The semiconservative model of DNA replication is like making a photo from a negative and then a new negative from the photo. In each new negative and photo pair, the new item was made from an old item.
- #17 Figure 10.4A-s3 A template model for DNA replication (step 3)
- #18 Figure 10.4B The untwisting and replication of DNA
- #19 Student Misconceptions and Concerns The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips 1. To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter. 2. There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one error in every 1 billion words.
- #20 Figure 10.5A Multiple bubbles in replicating DNA
- #21 Student Misconceptions and Concerns The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips 1. To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter. 2. There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one error in every 1 billion words.
- #22 Student Misconceptions and Concerns The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips 1. To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter. 2. There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one error in every 1 billion words.
- #23 Figure 10.5C How daughter DNA strands are synthesized
- #24 Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Consider placing the basic content from Figure 10.6A on the board, noting the sequence, products, and locations of transcription and translation in eukaryotic cells. This reminder can create a quick concept check for students as they learn additional detail. Teaching Tips 1. It has been said that everything about an organism is an interaction between the genome and the environment. You might wish to challenge your students to evaluate the validity of this statement. 2. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids.
- #25 Figure 10.6A_s3 The flow of genetic information in a eukaryotic cell (step 3)
- #26 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. The transcription of DNA into RNA is like a reporter’s transcription of a political speech. In both situations, the language remains the same, although in the case of the reporter, it changes its form from spoken to written language. 2. The sequential information in DNA and RNA is analogous to the sequential information in the letters of a sentence. This analogy is also helpful when explaining the impact of insertion or deletion mutations that cause a shift in the reading frame (see Module 10.16).
- #27 Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. As students learn about transcription, they might wonder which of the two strands of DNA is read. This uncertainty may add to the confusion about the details of the process, and students might not even think to ask. As noted in Module 10.9, the location of the promoter, a specific binding site for RNA polymerase, determines which strand is read. Teaching Tips Another advantage to the use of RNA to direct protein synthesis is that the original code (DNA) remains safely within the nucleus, away from the many potentially damaging chemicals in the cytoplasm. This is like making photocopies of important documents for study, keeping the originals safely stored away.
- #28 Figure 10.8B_s3 Deciphering the genetic information in DNA (step 3)
- #29 Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. As students learn about transcription, they might wonder which of the two strands of DNA is read. This uncertainty may add to the confusion about the details of the process, and students might not even think to ask. As noted in Module 10.9, the location of the promoter, a specific binding site for RNA polymerase, determines which strand is read. Teaching Tips Another advantage to the use of RNA to direct protein synthesis is that the original code (DNA) remains safely within the nucleus, away from the many potentially damaging chemicals in the cytoplasm. This is like making photocopies of important documents for study, keeping the originals safely stored away.
- #30 Figure 10.9A A close-up view of transcription
- #31 Figure 10.9B The transcription of a gene
- #32 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips Many analogies can be developed to represent the selective expression of a gene requiring the deletion of introns. Instructors that only assign some modules of a chapter are treating the chapters like sections of exons and introns, portions to be read and portions to be skipped. Alternately, students who highlight a chapter might be thought of as editing the book into exons, portions to be reviewed, and introns, nonhighlighted sections that will not be studied. Both analogies are imperfect, but may still convey the concept of selective reading.
- #33 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips Many analogies can be developed to represent the selective expression of a gene requiring the deletion of introns. Instructors that only assign some modules of a chapter are treating the chapters like sections of exons and introns, portions to be read and portions to be skipped. Alternately, students who highlight a chapter might be thought of as editing the book into exons, portions to be reviewed, and introns, nonhighlighted sections that will not be studied. Both analogies are imperfect, but may still convey the concept of selective reading.
- #34 Figure 10.10 The production of eukaryotic mRNA
- #35 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. You may want to note the parallel between the discovery in 1799 of the Rosetta stone, which provided the key that enabled scholars to crack the previously indecipherable hieroglyphic code, and the cracking of the genetic code in 1961. Consider challenging your students to explain what part of the genetic code is similar to the Rosetta stone. This could be a short in-class activity for small groups. 2. The authors note the universal use of the genetic code in all forms of life. The evolutionary significance of this fundamental, universal language is a reminder of the shared ancestry of all life. The universal genetic code is part of the overwhelming evidence for evolution.
- #36 Figure 10.8A Dictionary of the genetic code (RNA codons)
- #37 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips The unique structure of tRNA, with binding sites for an amino acid and its codon, permits the translation of the genetic code. Like an interpreter who speaks two languages, the tRNA molecules match codons to the specified amino acid.
- #38 Figure 10.12B A ribosome with empty binding sites
- #39 Figure 10.12C A ribosome with occupied binding sites
- #40 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. Ribosomal RNA is transcribed in the nucleolus of eukaryotic cells. The ribosomal subunits are assembled in the nucleus using proteins imported from the cytosol. These subunits are then exported to the cytosol, where they are only assembled into a functional ribosome when they attach to an mRNA molecule. Some of these details are not specifically noted in the text, but may be required to fill out your explanations. 2. If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them.
- #41 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. Ribosomal RNA is transcribed in the nucleolus of eukaryotic cells. The ribosomal subunits are assembled in the nucleus using proteins imported from the cytosol. These subunits are then exported to the cytosol, where they are only assembled into a functional ribosome when they attach to an mRNA molecule. Some of these details are not specifically noted in the text, but may be required to fill out your explanations. 2. If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them.
- #42 Figure 10.13B The initiation of translation
- #43 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. Students might want to think of the A and P sites as stages in an assembly line. The A site is where a new amino acid is brought in, according to the blueprint of the codon on the mRNA. The P site is where the growing product/polypeptide is anchored as it is being built. To help students better remember details of translation, they might think of the letters for the two sites as meaning A for addition, where an amino acid is added, and P for polypeptide, where the growing polypeptide is located. 2. If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them.
- #44 Student Misconceptions and Concerns Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips 1. Students might want to think of the A and P sites as stages in an assembly line. The A site is where a new amino acid is brought in, according to the blueprint of the codon on the mRNA. The P site is where the growing product/polypeptide is anchored as it is being built. To help students better remember details of translation, they might think of the letters for the two sites as meaning A for addition, where an amino acid is added, and P for polypeptide, where the growing polypeptide is located. 2. If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them.
- #45 Figure 10.14_s4 Polypeptide elongation (step 4)
- #46 Figure 10.15 A summary of transcription and translation
- #47 Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolutionary mechanisms. In this sense, mutations may be considered a part of a creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a random shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!”
- #48 Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolutionary mechanisms. In this sense, mutations may be considered a part of a creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a random shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!”
- #49 Figure 10.16A The molecular basis of sickle-cell disease
- #50 Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolutionary mechanisms. In this sense, mutations may be considered a part of a creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a random shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!”
- #51 Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolutionary mechanisms. In this sense, mutations may be considered a part of a creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a random shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!”
- #52 Figure 10.16B Types of mutations and their effects
- #54 Student Misconceptions and Concerns 1. Students and many parents with young children expect antibiotics to be used to treat many respiratory infections, even though such infections may result from a virus. Students will benefit from a thorough explanation of why antibiotics are inappropriate for viral infections as well as the rising numbers of antibiotic-resistant bacteria that have evolved as a result of the overuse of antibiotics. 2. The success of modern medicine has perhaps led to overconfidence in our ability to treat disease. Students often do not understand that there are few successful treatments for viral infections. Instead, the best defense against viruses is prevention, by reducing the chances of contacting the virus and through the use of vaccines. Teaching Tips Students (and instructors) might enjoy thinking of a prophage as a smudge mark on the master copy of a class handout. The smudge is replicated every time the original is copied!
- #55 Student Misconceptions and Concerns 1. Students and many parents with young children expect antibiotics to be used to treat many respiratory infections, even though such infections may result from a virus. Students will benefit from a thorough explanation of why antibiotics are inappropriate for viral infections as well as the rising numbers of antibiotic-resistant bacteria that have evolved as a result of the overuse of antibiotics. 2. The success of modern medicine has perhaps led to overconfidence in our ability to treat disease. Students often do not understand that there are few successful treatments for viral infections. Instead, the best defense against viruses is prevention, by reducing the chances of contacting the virus and through the use of vaccines. Teaching Tips Students (and instructors) might enjoy thinking of a prophage as a smudge mark on the master copy of a class handout. The smudge is replicated every time the original is copied!
- #56 Figure 10.17_1 Two types of phage replication cycles (part 1)
- #57 Figure 10.17_2 Two types of phage replication cycles (part 2)
- #58 Student Misconceptions and Concerns 1. Students and many parents with young children expect antibiotics to be used to treat many respiratory infections, even though such infections may result from a virus. Students will benefit from a thorough explanation of why antibiotics are inappropriate for viral infections as well as the rising numbers of antibiotic-resistant bacteria that have evolved as a result of the overuse of antibiotics. 2. The success of modern medicine has perhaps led to overconfidence in our ability to treat disease. Students often do not understand that there are few successful treatments for viral infections. Instead, the best defense against viruses is prevention, by reducing the chances of contacting the virus and through the use of vaccines. Teaching Tips 1. There is an interesting relationship between the speed at which a virus kills or debilitates a host and the extent to which it spreads from one organism to another. This is something to consider for a class discussion. Compare two viral infections. Infection A multiplies within the host, is spread by the host to other people through casual contact, but does not cause its lethal symptoms until 5–10 years after infection. Virus B kills the host within 1–2 days of infection, is easily transmitted, and causes severe symptoms within hours of contact. Which virus is likely to spread the fastest through the human population on Earth? Which might be considered the most dangerous to humans? 2. Students might wonder why a person needs to get a new seasonal flu vaccination every year. The annual mutations and variations in flu viruses require the production of a new flu vaccine annually. The Centers for Disease Control and Prevention monitors patterns of flu outbreaks, especially in Asia (where many variations of flu viruses originate). They must predict which strains are most likely to be dangerous in the coming year and then synthesize an appropriate vaccine.
- #59 Student Misconceptions and Concerns 1. Students and many parents with young children expect antibiotics to be used to treat many respiratory infections, even though such infections may result from a virus. Students will benefit from a thorough explanation of why antibiotics are inappropriate for viral infections as well as the rising numbers of antibiotic-resistant bacteria that have evolved as a result of the overuse of antibiotics. 2. The success of modern medicine has perhaps led to overconfidence in our ability to treat disease. Students often do not understand that there are few successful treatments for viral infections. Instead, the best defense against viruses is prevention, by reducing the chances of contacting the virus and through the use of vaccines. Teaching Tips 1. There is an interesting relationship between the speed at which a virus kills or debilitates a host and the extent to which it spreads from one organism to another. This is something to consider for a class discussion. Compare two viral infections. Infection A multiplies within the host, is spread by the host to other people through casual contact, but does not cause its lethal symptoms until 5–10 years after infection. Virus B kills the host within 1–2 days of infection, is easily transmitted, and causes severe symptoms within hours of contact. Which virus is likely to spread the fastest through the human population on Earth? Which might be considered the most dangerous to humans? 2. Students might wonder why a person needs to get a new seasonal flu vaccination every year. The annual mutations and variations in flu viruses require the production of a new flu vaccine annually. The Centers for Disease Control and Prevention monitors patterns of flu outbreaks, especially in Asia (where many variations of flu viruses originate). They must predict which strains are most likely to be dangerous in the coming year and then synthesize an appropriate vaccine.
- #60 Student Misconceptions and Concerns 1. Students and many parents with young children expect antibiotics to be used to treat many respiratory infections, even though such infections may result from a virus. Students will benefit from a thorough explanation of why antibiotics are inappropriate for viral infections as well as the rising numbers of antibiotic-resistant bacteria that have evolved as a result of the overuse of antibiotics. 2. The success of modern medicine has perhaps led to overconfidence in our ability to treat disease. Students often do not understand that there are few successful treatments for viral infections. Instead, the best defense against viruses is prevention, by reducing the chances of contacting the virus and through the use of vaccines. Teaching Tips 1. The authors note that the figures in Module 10.22 represent the size of the bacterial chromosome as much smaller than they actually are. They note that a bacterial chromosome is hundreds of times longer than the cell. These chromosomes use extensive folding to fit inside the cell. 2. You might challenge students to explain why conjugation is sometimes called bacterial sex. Students might note that two organisms cooperate to produce a new, genetically unique bacterium.
- #61 Figure 10.22D The integration of donated DNA into the recipient cell’s chromosome