1. © 2010 Pearson Education, Inc. Lectures by Chris C. Romero, updated by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Chapter 10 The Structure and Function of DNA

2. Biology and Society: Tracking a Killer The influenza virus is one of the deadliest pathogens in the world. Each year in the United States, over 20,000 people die from influenza infection. In the flu of 1918–1919, about 40 million people died worldwide. © 2010 Pearson Education, Inc.

3. Figure 10.00a

4. Figure 10.00b

5. © 2010 Pearson Education, Inc. Vaccines against the flu are the best way to protect public health. Because flu viruses mutate quickly, new vaccines must be created every year.

6. © 2010 Pearson Education, Inc. DNA: STRUCTURE AND REPLICATION DNA: –Was known to be a chemical in cells by the end of the nineteenth century –Has the capacity to store genetic information –Can be copied and passed from generation to generation

7. © 2010 Pearson Education, Inc. DNA and RNA Structure DNA and RNA are nucleic acids. –They consist of chemical units called nucleotides. –The nucleotides are joined by a sugar-phosphate backbone.

8. Sugar-phosphate backbone Phosphate group Nitrogenous base DNA nucleotide Nucleotide Thymine (T) Sugar Polynucleotide DNA double helix Sugar (deoxyribose) Phosphate group Nitrogenous base (can be A, G, C, or T) Figure 10.1

9. © 2010 Pearson Education, Inc. The four nucleotides found in DNA differ in their nitrogenous bases. These bases are: –Thymine (T) –Cytosine (C) –Adenine (A) –Guanine (G) RNA has uracil (U) in place of thymine.

10. © 2010 Pearson Education, Inc. Watson and Crick’s Discovery of the Double Helix James Watson and Francis Crick determined that DNA is a double helix.

11. James Watson (left) and Francis Crick Figure 10.3a

12. © 2010 Pearson Education, Inc. Watson and Crick used X-ray crystallography data to reveal the basic shape of DNA. –Rosalind Franklin collected the X-ray crystallography data.

13. X-ray image of DNA Rosalind Franklin Figure 10.3b

14. © 2010 Pearson Education, Inc. The model of DNA is like a rope ladder twisted into a spiral. –The ropes at the sides represent the sugar-phosphate backbones. –Each wooden rung represents a pair of bases connected by hydrogen bonds.

15. Twist Figure 10.4

16. © 2010 Pearson Education, Inc. DNA bases pair in a complementary fashion: –Adenine (A) pairs with thymine (T) –Cytosine (C) pairs with guanine (G)

17. (c) Computer model (b) Atomic model (a) Ribbon model Hydrogen bond Figure 10.5

18. © 2010 Pearson Education, Inc. DNA Replication When a cell reproduces, a complete copy of the DNA must pass from one generation to the next. Watson and Crick’s model for DNA suggested that DNA replicates by a template mechanism.

19. Parental (old) DNA molecule Daughter (new) strand Daughter DNA molecules (double helices) Figure 10.6

20. © 2010 Pearson Education, Inc. DNA can be damaged by ultraviolet light. DNA polymerases: –Are enzymes –Make the covalent bonds between the nucleotides of a new DNA strand –Are involved in repairing damaged DNA

21. © 2010 Pearson Education, Inc. DNA replication in eukaryotes: –Begins at specific sites on a double helix –Proceeds in both directions

22. Origin of replication Origin of replication Origin of replication Parental strands Parental strand Daughter strand Two daughter DNA molecules Bubble Figure 10.7

23. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN DNA functions as the inherited directions for a cell or organism. How are these directions carried out? © 2010 Pearson Education, Inc.

24. How an Organism’s Genotype Determines Its Phenotype An organism’s genotype is its genetic makeup, the sequence of nucleotide bases in DNA. The phenotype is the organism’s physical traits, which arise from the actions of a wide variety of proteins. © 2010 Pearson Education, Inc.

25. DNA specifies the synthesis of proteins in two stages: –Transcription, the transfer of genetic information from DNA into an RNA molecule –Translation, the transfer of information from RNA into a protein

26. TRANSLATION Protein RNA TRANSCRIPTION DNA Cytoplasm Nucleus Figure 10.8-3

27. © 2010 Pearson Education, Inc. The function of a gene is to dictate the production of a polypeptide. A protein may consist of two or more different polypeptides.

28. © 2010 Pearson Education, Inc. From Nucleotides to Amino Acids: An Overview Genetic information in DNA is: –Transcribed into RNA, then –Translated into polypeptides

29. © 2010 Pearson Education, Inc. What is the language of nucleic acids? –In DNA, it is the linear sequence of nucleotide bases. –A typical gene consists of thousands of nucleotides. –A single DNA molecule may contain thousands of genes.

30. © 2010 Pearson Education, Inc. When DNA is transcribed, the result is an RNA molecule. RNA is then translated into a sequence of amino acids in a polypeptide.

31. Figure 10.9

32. © 2010 Pearson Education, Inc. What are the rules for translating the RNA message into a polypeptide? A codon is a triplet of bases, which codes for one amino acid.

33. © 2010 Pearson Education, Inc. The Genetic Code The genetic code is: –The set of rules relating nucleotide sequence to amino acid sequence –Shared by all organisms

34. © 2010 Pearson Education, Inc. Of the 64 triplets: –61 code for amino acids –3 are stop codons, indicating the end of a polypeptide

35. TRANSLATION Amino acid RNA TRANSCRIPTION DNA strand Polypeptide Codon Gene 1 Gene 3 Gene 2 DNA molecule Figure 10.10

36. Second base of RNA codon First base of RNA codon Phenylalanine (Phe) Leucine (Leu) Cysteine (Cys) Leucine (Leu) Isoleucine (Ile) Valine (Val) Met or start Serine (Ser) Proline (Pro) Threonine (Thr) Tyrosine (Tyr) Histidine (His) Glutamine (Gln) Asparagine (Asn) Alanine (Ala) Stop Glutamic acid (Glu) Aspartic acid (Asp) Lysine (Lys) Arginine (Arg) Tryptophan (Trp) Arginine (Arg) Serine (Ser) Glycine (Gly) Third base of RNA codon Figure 10.11

37. © 2010 Pearson Education, Inc. Transcription: From DNA to RNA Transcription: –Makes RNA from a DNA template –Uses a process that resembles DNA replication –Substitutes uracil (U) for thymine (T) RNA nucleotides are linked by RNA polymerase.

38. © 2010 Pearson Education, Inc. Initiation of Transcription The “start transcribing” signal is a nucleotide sequence called a promoter. The first phase of transcription is initiation, in which: –RNA polymerase attaches to the promoter –RNA synthesis begins

39. © 2010 Pearson Education, Inc. RNA Elongation During the second phase of transcription, called elongation: –The RNA grows longer –The RNA strand peels away from the DNA template

40. © 2010 Pearson Education, Inc. Termination of Transcription During the third phase of transcription, called termination: –RNA polymerase reaches a sequence of DNA bases called a terminator –Polymerase detaches from the RNA –The DNA strands rejoin

41. © 2010 Pearson Education, Inc. The Processing of Eukaryotic RNA After transcription: –Eukaryotic cells process RNA –Prokaryotic cells do not

42. © 2010 Pearson Education, Inc. RNA processing includes: –Adding a cap and tail –Removing introns –Splicing exons together to form messenger RNA (mRNA)

43. Newly made RNA RNA nucleotides RNA polymerase Template strand of DNA Direction of transcription (a) A close-up view of transcription (b) Transcription of a gene RNA polymerase Completed RNA Growing RNA Termination Elongation Initiation Terminator DNA Area shown in part (a) at left RNA Promoter DNA RNA polymerase DNA of gene Figure 10.13

44. © 2010 Pearson Education, Inc. Translation: The Players Translation is the conversion from the nucleic acid language to the protein language.

45. © 2010 Pearson Education, Inc. Messenger RNA (mRNA) Translation requires: –mRNA –ATP –Enzymes –Ribosomes –Transfer RNA (tRNA)

46. Transcription Addition of cap and tail Coding sequence mRNA DNA Cytoplasm Nucleus Exons spliced together Introns removed Tail Cap RNA transcript with cap and tail Exon Intron Figure 10.14

47. © 2010 Pearson Education, Inc. Transfer RNA (tRNA) Transfer RNA (tRNA): –Acts as a molecular interpreter –Carries amino acids –Matches amino acids with codons in mRNA using anticodons

48. tRNA polynucleotide (ribbon model) RNA polynucleotide chain Anticodon Hydrogen bond Amino acid attachment site tRNA (simplified representation) Figure 10.15

49. © 2010 Pearson Education, Inc. Ribosomes Ribosomes are organelles that: –Coordinate the functions of mRNA and tRNA –Are made of two protein subunits –Contain ribosomal RNA (rRNA)

50. © 2010 Pearson Education, Inc. A fully assembled ribosome holds tRNA and mRNA for use in translation.

51. Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNA tRNA binding sites Codons Ribosome (b) The “players” of translation (a) A simplified diagram of a ribosome Large subunit Small subunit P site mRNA binding site A site Figure 10.16

52. © 2010 Pearson Education, Inc. Translation: The Process Translation is divided into three phases: –Initiation –Elongation –Termination

53. © 2010 Pearson Education, Inc. Initiation Initiation brings together: –mRNA –The first amino acid, Met, with its attached tRNA –Two subunits of the ribosome The mRNA molecule has a cap and tail that help it bind to the ribosome.

54. Start of genetic message Tail End Cap Figure 10.17

55. © 2010 Pearson Education, Inc. Initiation occurs in two steps: –First, an mRNA molecule binds to a small ribosomal subunit, then an initiator tRNA binds to the start codon. –Second, a large ribosomal subunit binds, creating a functional ribosome.

56. Initiator tRNA mRNA Start codon Met P site Small ribosomal subunit A site Large ribosomal subunit Figure 10.18

57. © 2010 Pearson Education, Inc. Elongation Elongation occurs in three steps. –Step 1, codon recognition: –the anticodon of an incoming tRNA pairs with the mRNA codon at the A site of the ribosome.

58. © 2010 Pearson Education, Inc. –Step 2, peptide bond formation: –The polypeptide leaves the tRNA in the P site and attaches to the amino acid on the tRNA in the A site –The ribosome catalyzes the bond formation between the two amino acids

59. © 2010 Pearson Education, Inc. –Step 3, translocation: –The P site tRNA leaves the ribosome –The tRNA carrying the polypeptide moves from the A to the P site

60. New peptide bond Stop codon mRNA movement mRNA P site Translocation Peptide bond formation Polypeptide ELONGATION Codon recognition A site Codons Anticodon Amino acid Figure 10.19-4

61. © 2010 Pearson Education, Inc. Termination Elongation continues until: –The ribosome reaches a stop codon –The completed polypeptide is freed –The ribosome splits into its subunits

62. © 2010 Pearson Education, Inc. Review: DNA  RNA  Protein In a cell, genetic information flows from DNA to RNA in the nucleus and RNA to protein in the cytoplasm.

63. Transcription RNA polymerase mRNA DNA Intron Nucleus mRNA Intron Tail Cap RNA processing tRNA Amino acid attachment Enzyme ATP Initiation of translation Ribosomal subunits Elongation Anticodon Codon Termination Polypeptide Stop codon Figure 10.20-6

64. © 2010 Pearson Education, Inc. As it is made, a polypeptide: – Coils and folds –Assumes a three-dimensional shape, its tertiary structure Several polypeptides may come together, forming a protein with quaternary structure.

65. © 2010 Pearson Education, Inc. Transcription and translation are how genes control: –The structures –The activities of cells

66. © 2010 Pearson Education, Inc. Mutations A mutation is any change in the nucleotide sequence of DNA. Mutations can change the amino acids in a protein. Mutations can involve: –Large regions of a chromosome –Just a single nucleotide pair, as occurs in sickle cell anemia

67. © 2010 Pearson Education, Inc. Types of Mutations Mutations within a gene can occur as a result of: –Base substitution, the replacement of one base by another –Nucleotide deletion, the loss of a nucleotide –Nucleotide insertion, the addition of a nucleotide

68. Normal hemoglobin DNA mRNA Normal hemoglobin Mutant hemoglobin DNA mRNA Sickle-cell hemoglobin Figure 10.21

69. © 2010 Pearson Education, Inc. Insertions and deletions can: –Change the reading frame of the genetic message –Lead to disastrous effects

70. © 2010 Pearson Education, Inc. Mutagens Mutations may result from: –Errors in DNA replication –Physical or chemical agents called mutagens

71. © 2010 Pearson Education, Inc. Although mutations are often harmful, they are the source of genetic diversity, which is necessary for evolution by natural selection.

72. mRNA and protein from a normal gene Deleted (a) Base substitution Inserted (b) Nucleotide deletion (c) Nucleotide insertion Figure 10.22

73. © 2010 Pearson Education, Inc. VIRUSES AND OTHER NONCELLULAR INFECTIOUS AGENTS Viruses exhibit some, but not all, characteristics of living organisms. Viruses: –Possess genetic material in the form of nucleic acids –Are not cellular and cannot reproduce on their own.

74. © 2010 Pearson Education, Inc. Bacteriophages Bacteriophages, or phages, are viruses that attack bacteria.

75. Protein coat DNA Figure 10.24

77. © 2010 Pearson Education, Inc. Phages have two reproductive cycles. (1) In the lytic cycle: –Many copies of the phage are made within the bacterial cell, and then –The bacterium lyses (breaks open)

78. © 2010 Pearson Education, Inc. (2) In the lysogenic cycle: –The phage DNA inserts into the bacterial chromosome and –The bacterium reproduces normally, copying the phage at each cell division

79. Bacterial cell Head Tail fiber DNA of virus Bacteriophage (200 nm tall) Colorized TEM Figure 10.25

80. © 2010 Pearson Education, Inc. Plant Viruses Viruses that infect plants can: –Stunt growth –Diminish plant yields –Spread throughout the entire plant

81. Phage Phage DNA Phage injects DNA Phage attaches to cell. Bacterial chromosome (DNA) Phage DNA circularizes. Phages assemble OR New phage DNA and proteins are synthesized. LYTIC CYCLE Cell lyses, releasing phages. LYSOGENIC CYCLE Phage DNA is inserted into the bacterial chromosome. Many cell divisions Prophage Occasionally a prophage may leave the bacterial chromosome. Lysogenic bacterium reproduces normally, replicating the prophage at each cell division. Figure 10.26-2

82. Phage lambda E. coli Figure 10.26c

83. © 2010 Pearson Education, Inc. Viral plant diseases: –Have no cure –Are best prevented by producing plants that resist viral infection

84. Tobacco mosaic virus RNA Protein Figure 10.27

85. Figure 10.27b

86. Tobacco mosaic virus RNA Protein Figure 10.27a

87. © 2010 Pearson Education, Inc. Animal Viruses Viruses that infect animals are: –Common causes of disease –May have RNA or DNA genomes Some animal viruses steal a bit of host cell membrane as a protective envelope.

88. Protein coat RNA Protein spike Membranous envelope Figure 10.28

89. © 2010 Pearson Education, Inc. The reproductive cycle of an enveloped RNA virus can be broken into seven steps.

90. Protein coat mRNA Protein spike Plasma membrane of host cell Envelope Template New viral genome New viral proteins Exit Virus Viral RNA (genome) Viral RNA (genome) Entry Uncoating Assembly RNA synthesis by viral enzyme RNA synthesis (other strand) Protein synthesis Figure 10.29

91. Protein spike Envelope Mumps virus Colorized TEM Figure 10.29c

92. The Process of Science: Do Flu Vaccines Protect the Elderly? Observation: Vaccination rates among the elderly rose from 15% in 1980 to 65% in 1996. Question: Do flu vaccines decrease the mortality rate among those elderly people who receive them? Hypothesis: Elderly people who were immunized would have fewer hospital stays and deaths during the winter after vaccination. © 2010 Pearson Education, Inc.

93. Experiment: Tens of thousands of people over the age of 65 were followed during the ten flu seasons of the 1990s. Results: People who were vaccinated had a: –27% less chance of being hospitalized during the next flu season and –48% less chance of dying

94. Deaths Hospitalizations Percent reduction in severe illness and death in vaccinated group Winter months (flu season) Summer months (non-flu season) 16 0 27 48 50 20 40 30 10 0 Figure 10.30a

95. Figure 10.30b

96. © 2010 Pearson Education, Inc. HIV, the AIDS Virus HIV is a retrovirus, an RNA virus that reproduces by means of a DNA molecule. Retroviruses use the enzyme reverse transcriptase to synthesize DNA on an RNA template. HIV steals a bit of host cell membrane as a protective envelope.

97. Envelope Reverse transcriptase Surface protein Protein coat RNA (two identical strands) Figure 10.31

98. © 2010 Pearson Education, Inc. The behavior of HIV nucleic acid in an infected cell can be broken into six steps.

99. Reverse transcriptase HIV (red dots) infecting a white blood cell DNA strand Chromosomal DNA Cytoplasm Nucleus Provirus RNA Viral RNA Double stranded DNA Viral RNA and proteins SEM Figure 10.32

100. © 2010 Pearson Education, Inc. AIDS (acquired immune deficiency syndrome) is: –Caused by HIV infection and –Treated with drugs that interfere with the reproduction of the virus

101. HIV (red dots) infecting a white blood cell SEM Figure 10.32b

102. Part of a T nucleotide Thymine (T) AZT Figure 10.33

103. © 2010 Pearson Education, Inc. Viroids and Prions Two classes of pathogens are smaller than viruses: –Viroids are small circular RNA molecules that do not encode proteins –Prions are misfolded proteins that somehow convert normal proteins to the misfolded prion version

104. © 2010 Pearson Education, Inc. Prions are responsible for neurodegenerative diseases including: –Mad cow disease –Scrapie in sheep and goats –Chronic wasting disease in deer and elk –Creutzfeldt-Jakob disease in humans

105. Figure 10.34

106. Evolution Connection: Emerging Viruses Emerging viruses are viruses that have: –Appeared suddenly or –Have only recently come to the attention of science © 2010 Pearson Education, Inc.

107. Avian flu: –Infects birds –Infected 18 people in 1997 –Since has spread to Europe and Africa infecting 300 people and killing 200 of them

108. © 2010 Pearson Education, Inc. If avian flu mutates to a form that can easily spread between people, the potential for a major human outbreak is significant.

109. Figure 10.35

110. © 2010 Pearson Education, Inc. New viruses can arise by: –Mutation of existing viruses –Spread to new host species