1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 17 From Gene to Protein

2. Overview: The Flow of Genetic Information The information content of DNA is in the form of specific sequences of nucleotides The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins Proteins are the links between genotype and phenotype Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

3. Fig. 17-1

4. Concept 17.1: Genes specify proteins via transcription and translation How was the fundamental relationship between genes and proteins discovered? Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

5. Evidence from the Study of Metabolic Defects In 1909, British physician Archibald Garrod first suggested that genes dictate phenotypes through enzymes that catalyze specific chemical reactions He thought symptoms of an inherited disease reflect an inability to synthesize a certain enzyme Linking genes to enzymes required understanding that cells synthesize and degrade molecules in a series of steps, a metabolic pathway Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

6. Nutritional Mutants in Neurospora: Scientific Inquiry George Beadle and Edward Tatum exposed bread mold to X-rays, creating mutants that were unable to survive on minimal medium as a result of inability to synthesize certain molecules Using crosses, they identified three classes of arginine-deficient mutants, each lacking a different enzyme necessary for synthesizing arginine They developed a one gene–one enzyme hypothesis, which states that each gene dictates production of a specific enzyme Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

7. Fig. 17-2 RESULTS EXPERIMENT CONCLUSION Growth: Wild-type cells growing and dividing No growth: Mutant cells cannot grow and divide Minimal medium Classes of Neurospora crassa Wild type Class I mutants Class II mutants Class III mutants Minimal medium (MM) (control) MM + ornithine MM + citrulline Condition MM + arginine (control) Class I mutants (mutation in gene A) Wild type Class II mutants (mutation in gene B) Class III mutants (mutation in gene C) Gene A Gene B Gene C Precursor Enzyme A Enzyme B Ornithine Enzyme B Citrulline Enzyme C Arginine

8. Fig. 17-2a EXPERIMENT Growth: Wild-type cells growing and dividing No growth: Mutant cells cannot grow and divide Minimal medium

9. Fig. 17-2b RESULTS Classes of Neurospora crassa Wild type Class I mutantsClass II mutants Class III mutants Minimal medium (MM) (control) MM + ornithine MM + citrulline MM + arginine (control) Condition

10. Fig. 17-2c CONCLUSION Class I mutants (mutation in gene A) Class II mutants (mutation in gene B) Class III mutants (mutation in gene C) Wild type Precursor Enzyme A Ornithine Enzyme B Citrulline Enzyme C Arginine Gene A Gene B Gene C

11. The Products of Gene Expression: A Developing Story Some proteins aren’t enzymes, so researchers later revised the hypothesis: one gene–one protein Many proteins are composed of several polypeptides, each of which has its own gene Therefore, Beadle and Tatum’s hypothesis is now restated as the one gene–one polypeptide hypothesis Note that it is common to refer to gene products as proteins rather than polypeptides Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

12. Basic Principles of Transcription and Translation RNA is the intermediate between genes and the proteins for which they code Transcription is the synthesis of RNA under the direction of DNA Transcription produces messenger RNA (mRNA) Translation is the synthesis of a polypeptide, which occurs under the direction of mRNA Ribosomes are the sites of translation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

13. In prokaryotes, mRNA produced by transcription is immediately translated without more processing In a eukaryotic cell, the nuclear envelope separates transcription from translation Eukaryotic RNA transcripts are modified through RNA processing to yield finished mRNA Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

14. A primary transcript is the initial RNA transcript from any gene The central dogma is the concept that cells are governed by a cellular chain of command: DNA  RNA  protein Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

15. Fig. 17-3 TRANSCRIPTION TRANSLATION DNA mRNA Ribosome Polypeptide (a) Bacterial cell Nuclear envelope TRANSCRIPTION RNA PROCESSING Pre-mRNA DNA mRNA TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell

16. Fig. 17-3a-1 TRANSCRIPTION DNA mRNA (a) Bacterial cell

17. Fig. 17-3a-2 (a) Bacterial cell TRANSCRIPTION DNA mRNA TRANSLATION Ribosome Polypeptide

18. Fig. 17-3b-1 (b) Eukaryotic cell TRANSCRIPTION Nuclear envelope DNA Pre-mRNA

19. Fig. 17-3b-2 (b) Eukaryotic cell TRANSCRIPTION Nuclear envelope DNA Pre-mRNA RNA PROCESSING mRNA

20. Fig. 17-3b-3 (b) Eukaryotic cell TRANSCRIPTION Nuclear envelope DNA Pre-mRNA RNA PROCESSING mRNA TRANSLATION Ribosome Polypeptide

21. The Genetic Code To make a protein, the gene that codes for it unwinds in the nucleus and exposes the DNA to transcription enzymes, particularly RNA Polymerase. The nucleotides are read by RNA Polymerase from 5’ to 3’. So, DNA is replaced by RNA in this first step. Uracil replaces Thymine in RNA. The RNA strand, called pre-mRNA, is first processed before it can leave the nucleus. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

22. Upon leaving the nucleus, mRNA attaches to a ribosome in the cytoplasm. During translation, mRNA is read by the ribosome, 3 nucleotides at a time in the 5’ to 3’ direction. These are codons. Each codon specifies a specific amino acid, brought by tRNA, to be placed along the growing polypeptide chain, coming off the ribosome. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

23. Example: AGT at a particular position on a DNA strand on a gene results in the corresponding mRNA strand to transcribe to UCA. On the ribosome, UCA translates to placement of the amino acid Serine. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

24. Codons: Triplets of Bases How many combinations of four RNA nucleotides (A, C, U, G) in groups of three (codons) are possible? Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

25. Fig. 17-4 DNA molecule Gene 1 Gene 2 Gene 3 DNA template strand TRANSCRIPTION TRANSLATION mRNA Protein Codon Amino acid

26. Cracking the Code Of the 64 codons, 61 code for amino acids, including Methionine, the “start” codon for every gene. 3 codons are “stop” signals that end translation The genetic code is nearly universal, shared by the simplest bacteria to the most complex animal. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

27. Fig. 17-5 Second mRNA base First mRNA base (5 end of codon) Third mRNA base (3 end of codon)

28. Evolution of the Genetic Code Genes can be transcribed and translated after being transplanted from one species to another Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

29. Fig. 17-6 (a) Tobacco plant expressing a firefly gene (b) Pig expressing a jellyfish gene

30. Fig. 17-6a (a) Tobacco plant expressing a firefly gene

31. Fig. 17-6b (b) Pig expressing a jellyfish gene

32. Concept 17.2: Transcription is the DNA-directed synthesis of RNA: a closer look Transcription, the first stage of gene expression, can be examined in more detail Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

33. Molecular Components of Transcription RNA synthesis, or Transcription, is catalyzed by RNA polymerase, which pries the DNA strands apart and hooks together the RNA nucleotides Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

34. The DNA sequence where RNA polymerase attaches is called the promoter; in bacteria, the sequence signaling the end of transcription is called the terminator The stretch of DNA that is transcribed is called a transcription unit Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: Transcription Animation: Transcription

35. Synthesis of an RNA Transcript The three stages of transcription: – Initiation – Elongation – Termination Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

36. Fig. 17-7a-1 Promoter Transcription unit DNA Start point RNA polymerase 5 5 3 3

37. Fig. 17-7a-2 Promoter Transcription unit DNA Start point RNA polymerase 5 5 3 3 Initiation 3 3 1 mRNA transcript 5 5 Unwound DNA Template strand of DNA

38. Fig. 17-7a-3 Promoter Transcription unit DNA Start point RNA polymerase 5 5 3 3 Initiation 3 3 1 mRNA transcript 5 5 Unwound DNA Template strand of DNA 2 Elongation Rewound DNA 5 5 5 3 3 3 mRNA transcript Note that an mRNA transcript is being produced in a 5’ to 3’ direction.

39. Fig. 17-7a-4 Promoter Transcription unit DNA Start point RNA polymerase 5 5 3 3 Initiation 3 3 1 mRNA transcript 5 5 Unwound DNA Template strand of DNA 2 Elongation Rewound DNA 5 5 5 3 3 3 mRNA transcript 3 Termination 5 5 5 3 3 3 Completed mRNA transcript

40. Fig. 17-7b Elongation RNA polymerase Nontemplate strand of DNA RNA nucleotides 3 end Direction of transcription (“downstream”) Template strand of DNA Newly made mRNA 3 5 5

41. Fig. 17-7 Promoter Transcription unit Start point DNA RNA polymerase 5 53 3 Initiation 1 2 3 5 5 3 3 Unwound DNA RNA transcript Template strand of DNA Elongation Rewound DNA 5 5 5 5 5 3 3 3 3 mRNA transcript Termination 5 5 3 3 3 5 Completed mRNA transcript Newly made mRNA Template strand of DNA Direction of transcription (“downstream”) 3 end RNA polymerase RNA nucleotides Nontemplate strand of DNA Elongation

42. RNA Polymerase Binding and Initiation of Transcription Let’s examine the very start of Transcription in a bit more detail… Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings 3

43. Fig. 17-8 A eukaryotic promoter includes a TATA box 3 2 3 Promoter TATA box Start point (TAC) Template 5 3 5 Transcription factors Several proteins, including histones, must bind to the DNA before RNA polymerase II can do so. 5 53 3 RNA polymerase II 5 5 5 3 3 mRNA transcript initiated Transcription initiation complex 3 3 3

44. Elongation of the RNA Strand mRNA is transcribed at a rate of 40 nucleotides per second in eukaryotes A gene can be transcribed into mRNA by multiple RNA polymerases simultaneously, creating many mRNA strands from one unwound gene. This is called “gene amplification”. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

45. Concept 17.3: Eukaryotic cells modify RNA after transcription Once formed, the mRNA molecule is not quite ready for Translation. Enzymes in the eukaryotic nucleus must modify the new mRNA strands (actually called pre-mRNA) before the genetic messages are dispatched to the cytoplasm This is called RNA Processing. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

46. Alteration of Pre-mRNA Pre-mRNA molecule is processed in three ways: – The 5 end is capped with GTP – The 3 end is tailed with lots of Adenines – “introns” (non-coding segments) are cut out These modifications help export mRNA and attach it to a ribosome. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

47. Fig. 17-10 Pre-mRNA mRNA Coding segment Introns cut out and exons spliced together 5 Cap Exon Intron 5 ExonIntron Exon 3 Poly-A tail 5 Cap GTPAAAAA….

48. Fig. 17-9 Protein-coding segment Polyadenylation signal 3 3 UTR5 UTR 5 5 Cap Start codon Stop codon Poly-A tail G PPPAAUAAA AAA …

49. Split Genes and RNA Splicing Intron sections are usually much longer than the sections of mRNA coded into protein Regions to be coded into protein are called exons, because they are eventually ex pressed into amino acid sequences RNA splicing removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

50. In some cases, RNA splicing is carried out by spliceosomes Spliceosomes consist of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

51. Fig. 17-11-1 RNA transcript (pre-mRNA) Exon 1Exon 2Intron Protein snRNA snRNPs Other proteins 5

52. Fig. 17-11-2 RNA transcript (pre-mRNA) Exon 1Exon 2Intron Protein snRNA snRNPs Other proteins 5 5 Spliceosome

53. Fig. 17-11-3 RNA transcript (pre-mRNA) Exon 1Exon 2Intron Protein snRNA snRNPs Other proteins 5 5 Spliceosome components Cut-out intron mRNA Exon 1 Exon 2 5

54. The Functional and Evolutionary Importance of Introns Many genes code for more than one kind of protein, depending on which segments are treated as exons during RNA processing! This is alternative RNA splicing, and the different proteins possible are called “domains” Therefore, the number of proteins an organism can produce is much greater than the number of its genes! Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

55. Abnormal domains are implicated in disease and cancer. However, new domains may also result in increased flexibility of the genome, and therefore may help further evolution of populations. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

56. Fig. 17-12 Gene DNA Exon 1Exon 2 Exon 3 Intron Transcription RNA processing Translation Domain 2 Domain 3 Domain 1 Polypeptide

57. Ribozymes Ribozymes are catalytic RNA molecules that function as enzymes and can splice RNA The discovery of ribozymes rendered obsolete the belief that all biological catalysts were proteins Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

58. Three properties of RNA enable it to function as an enzyme – It can form a three-dimensional structure because of its ability to base pair with itself – Some bases in RNA contain functional groups – RNA may hydrogen-bond with other nucleic acid molecules Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

59. Concept 17.4: Translation is the RNA-directed synthesis of a polypeptide: a closer look The translation of mRNA to protein can be examined in more detail Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

60. Molecular Components of Translation A cell translates an mRNA message into protein with the help of transfer RNA (tRNA) Molecules of tRNA are not identical: – Each carries a specific amino acid on one end – Each has an anticodon on the other end; the anticodon base-pairs with a complementary triplet codon on mRNA Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings BioFlix: Protein Synthesis BioFlix: Protein Synthesis

61. Fig. 17-13 Polypeptide Ribosome Amino acids tRNA with amino acid attached tRNA Anticodon Trp Phe Gly Codons 3 5 mRNA

62. The Structure and Function of Transfer RNA A C C A tRNA molecule consists of a single RNA strand that is only about 80 nucleotides long Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

63. Fig. 17-14a Amino acid attachment site (a) Two-dimensional structure Hydrogen bonds Anticodon 3 5

64. Fig. 17-14b Amino acid attachment site 3 3 5 5 Anticodon (b) Three-dimensional structure (c) Symbol used in this book How many different “anticodons” are possible???

65. Accurate translation requires two steps: – First: a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl- tRNA synthetase – Second: a correct match between the tRNA anticodon and an mRNA codon, done by a ribosome Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

66. Fig. 17-15-4 Amino acid Aminoacyl-tRNA synthetase (enzyme) ATP Adenosine PPP P P P i P P i i tRNA Aminoacyl-tRNA synthetase Computer model AMP Adenosine P Aminoacyl-tRNA (“charged tRNA”)

67. Ribosomes Ribosomes are composed of two subunits (“LSU” and “SSU”) are made of proteins and ribosomal RNA (rRNA) Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

68. A ribosome has three binding sites for tRNA: – The A site brings in the tRNA that carries the next amino acid to be added to the chain – The P site holds the tRNA that carries the growing polypeptide chain – The E site is the exit site, where discharged tRNAs leave the ribosome Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

69. Fig. 17-16a Growing polypeptide Exit tunnel tRNA molecules Large subunit Small subunit (a) Computer model of functioning ribosome mRNA E P A 5 3

70. Fig. 17-16b P site (Peptidyl-tRNA binding site) A site (Aminoacyl- tRNA binding site) E site (Exit site) mRNA binding site Large subunit Small subunit (b) Schematic model showing binding sites Next amino acid to be added to polypeptide chain Amino end Growing polypeptide mRNA tRNA EP A E Codons (c) Schematic model with mRNA and tRNA 5 3

71. Ribosome Association and Initiation of Translation The initiation stage of translation binds the small ribosomal subunit to the mRNA and a tRNA molecule Then the small subunit moves along the mRNA until it reaches the start codon (AUG) Secondly, the large ribosomal subunit attaches, and the protein can now be made. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

72. Fig. 17-17 3 3 5 5 U U A A C G Met GTP GDP Initiator tRNA mRNA 5 3 Start codon mRNA binding site Small ribosomal subunit 5 P site Translation initiation complex 3 EA Met Large ribosomal subunit

73. Elongation of the Polypeptide Chain During the elongation stage, amino acids, carried by tRNA molecules, are added one by one to the preceding amino acid Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

74. Fig. 17-18-1 Amino end of polypeptide mRNA 5 3 E P site A site

75. Fig. 17-18-2 Amino end of polypeptide mRNA 5 3 E P site A site GTP GDP E P A

76. Fig. 17-18-3 Amino end of polypeptide mRNA 5 3 E P site A site GTP GDP E P A E PA

77. Fig. 17-18-4 Amino end of polypeptide mRNA 5 3 E P site A site GTP GDP E P A E PA GTP Ribosome ready for next aminoacyl tRNA E P A

78. Termination of Translation Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome A stop codon adds a water molecule and not an amino acid to the polypeptide This reaction releases the polypeptide, and the translation assembly then comes apart Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: Translation Animation: Translation

79. Fig. 17-19-1 Release factor 3 5 Stop codon (UAG, UAA, or UGA)

80. Fig. 17-19-2 Release factor 3 5 Stop codon (UAG, UAA, or UGA) 5 3 2 Free polypeptide 2 GDP GTP

81. Fig. 17-19-3 Release factor 3 5 Stop codon (UAG, UAA, or UGA) 5 3 2 Free polypeptide 2 GDP GTP 5 3

82. Polyribosomes A number of ribosomes can translate a single mRNA simultaneously, forming a polyribosome (or polysome) Polyribosomes enable a cell to make many copies of a polypeptide very quickly Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

83. Fig. 17-20 Growing polypeptides Completed polypeptide Incoming ribosomal subunits Start of mRNA (5 end) Polyribosome End of mRNA (3 end) (a) Ribosomes mRNA (b) 0.1 µm

84. Completing and Targeting the Functional Protein Often translation is not sufficient to make a functional protein Polypeptide chains are modified after translation Completed proteins are targeted to specific sites in the cell Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

85. Protein Folding and Post-Translational Modifications During and after synthesis, a polypeptide chain spontaneously coils and folds into its three- dimensional shape Proteins may also require post-translational modifications before doing their job Some polypeptides are activated by enzymes that cleave them Other polypeptides come together to form the subunits of a protein Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

86. Targeting Polypeptides to Specific Locations Two populations of ribosomes are evident in cells: free ribsomes (in the cytosol) and bound ribosomes (attached to the ER) Free ribosomes mostly synthesize proteins that function in the cytosol Bound ribosomes make proteins of the endomembrane system and proteins that are secreted from the cell Ribosomes are identical and can switch from free to bound Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

87. Polypeptide synthesis always begins in the cytosol Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the ER Polypeptides destined for the ER or for secretion are marked by a signal peptide Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

88. A signal-recognition particle (SRP) binds to the signal peptide The SRP brings the signal peptide and its ribosome to the ER Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

89. Fig. 17-21 Ribosome mRNA Signal peptide Signal- recognition particle (SRP) CYTOSOL Translocation complex SRP receptor protein ER LUMEN Signal peptide removed ER membrane Protein

90. Concept 17.5: Point mutations can affect protein structure and function Mutations are changes in the genetic material of a cell or virus Point mutations are chemical changes in just one base pair of a gene The change of a single nucleotide in a DNA template strand can lead to the production of an abnormal protein Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

91. Types of Point Mutations Point mutations within a gene can be divided into two general categories – substitutions – insertions / deletions Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

92. Substitutions Silent mutations have no effect on the amino acid produced by a codon because of redundancy in the genetic code Missense mutations still code for an amino acid, but not necessarily the right amino acid Nonsense mutations change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

93. Fig. 17-23a Wild type 3 DNA template strand 3 3 5 5 5 mRNA Protein Amino end Stop Carboxyl end A instead of G 3 3 3 U instead of C 5 5 5 Stop Silent (no effect on amino acid sequence)

94. Fig. 17-23b Wild type DNA template strand 3 5 mRNA Protein 5 Amino end Stop Carboxyl end 5 3 3 T instead of C A instead of G 3 3 3 5 5 5 Stop Missense

95. Fig. 17-22 Wild-type hemoglobin DNA mRNA Mutant hemoglobin DNA mRNA 3 3 3 3 3 3 5 5 5 5 5 5 CCTT T T G G A A A A AA A GG U Normal hemoglobinSickle-cell hemoglobin Glu Val

96. Fig. 17-23c Wild type DNA template strand 3 5 mRNA Protein 5 Amino end Stop Carboxyl end 5 3 3 A instead of T U instead of A 3 3 3 5 5 5 Stop Nonsense

97. Insertions and Deletions Insertions and deletions have a disastrous effect on the resulting protein much more often than substitutions. Insertion or deletion of nucleotides may alter the reading frame, producing a frameshift mutation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

98. Fig. 17-23d Wild type DNA template strand 3 5 mRNA Protein 5 Amino end Stop Carboxyl end 5 3 3 Extra A Extra U 3 3 3 5 5 5 Stop Frameshift causing immediate nonsense (1 base-pair insertion)

99. Fig. 17-23e Wild type DNA template strand 3 5 mRNA Protein 5 Amino end Stop Carboxyl end 5 3 3 missing 3 3 3 5 5 5 Frameshift causing extensive missense (1 base-pair deletion)

100. Fig. 17-23f Wild type DNA template strand 3 5 mRNA Protein 5 Amino end Stop Carboxyl end 5 3 3 missing 3 3 3 5 5 5 No frameshift, but one amino acid missing (3 base-pair deletion) Stop

101. Mutagens Spontaneous mutations can occur during DNA replication, recombination, or repair Mutagens are physical or chemical agents that can cause mutations Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

102. Concept 17.6: While gene expression differs among the domains of life, the concept of a gene is universal Archaea are prokaryotes, but share many features of gene expression with eukaryotes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

103. Comparing Gene Expression in Bacteria, Archaea, and Eukarya Bacteria and eukarya differ in their RNA polymerases, termination of transcription and ribosomes; archaea tend to resemble eukarya in these respects Bacteria can simultaneously transcribe and translate the same gene In eukarya, transcription and translation are separated by the nuclear envelope In archaea, transcription and translation are likely coupled Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

104. Fig. 17-24 RNA polymerase DNA Polyribosome mRNA 0.25 µm Direction of transcription DNA RNA polymerase Polyribosome Polypeptide (amino end) Ribosome mRNA (5 end)

105. What Is a Gene? Revisiting the Question The idea of the gene itself is a unifying concept of life We have considered a gene as: – A discrete unit of inheritance – A region of specific nucleotide sequence in a chromosome – A DNA sequence that codes for a specific polypeptide chain Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

106. Fig. 17-25 TRANSCRIPTION RNA PROCESSING DNA RNA transcript 3 5 RNA polymerase Poly-A RNA transcript (pre-mRNA) Intron Exon NUCLEUS Aminoacyl-tRNA synthetase AMINO ACID ACTIVATION Amino acid tRNA CYTOPLASM Poly-A Growing polypeptide 3 Activated amino acid mRNA TRANSLATION Cap Ribosomal subunits Cap 5 E P A A Anticodon Ribosome Codon E

107. In summary, a gene can be defined as a region of DNA that can be expressed to produce a final functional product, either a polypeptide or an RNA molecule Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

108. Fig. 17-UN1 Transcription unit Promoter RNA transcript RNA polymerase Template strand of DNA 5 5 53 3 3

109. Fig. 17-UN2 Pre-mRNA Cap mRNA Poly-A tail

110. Fig. 17-UN3 mRNA Ribosome Polypeptide

111. Fig. 17-UN4

112. Fig. 17-UN5

113. Fig. 17-UN6

114. Fig. 17-UN7

115. Fig. 17-UN8

116. You should now be able to: 1.Describe the contributions made by Garrod, Beadle, and Tatum to our understanding of the relationship between genes and enzymes 2.Briefly explain how information flows from gene to protein 3.Compare transcription and translation in bacteria and eukaryotes 4.Explain what it means to say that the genetic code is redundant and unambiguous Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

117. 5.Include the following terms in a description of transcription: mRNA, RNA polymerase, the promoter, the terminator, the transcription unit, initiation, elongation, termination, and introns 6.Include the following terms in a description of translation: tRNA, wobble, ribosomes, initiation, elongation, and termination Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings