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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 17 From Gene to Protein Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Overview: The Flow of Genetic Information • The information content of DNA is in the form of specific sequences of _____________________ • The DNA inherited by an organism leads to specific traits by dictating the synthesis of _____________________ • _______________ are the links between genotype and phenotype • _________________, the process by which DNA directs protein synthesis, includes two stages: _________________ and __________________ © 2011 Pearson Education, Inc. Concept 17.1: Genes specify proteins via transcription and translation • How was the fundamental relationship between genes and proteins discovered? © 2011 Pearson Education, Inc. Evidence from the Study of Metabolic Defects • In 1902, British physician Archibald _________ first suggested that _______ dictate ___________ through enzymes that catalyze specific chemical reactions • He thought symptoms of an inherited disease reflect an inability to synthesize a certain _______ • _____________________________ required understanding that cells synthesize and degrade molecules in a series of steps, a metabolic pathway © 2011 Pearson Education, Inc. Nutritional Mutants in Neurospora: Scientific Inquiry • George ___________ and Edward__________ exposed bread mold to X-rays, creating mutants that were unable to survive on minimal media • Using crosses, they and their coworkers identified three classes of ______________________, each lacking a different enzyme necessary for synthesizing arginine • They developed a _________________________, which states that each gene dictates production of a specific enzyme © 2011 Pearson Education, Inc. Figure 17.2a EXPERIMENT Growth: Wild-type cells growing and dividing No growth: Mutant cells cannot grow and divide Minimal medium Figure 17.2b RESULTS Classes of Neurospora crassa Wild type Minimal medium (MM) (control) Growth Class I mutants Class II mutants Class III mutants No growth Condition MM ornithine MM citrulline MM arginine (control) Summary of results Can grow with or without any supplements Can grow on ornithine, citrulline, or arginine Can grow only on citrulline or arginine Require arginine to grow Figure 17.2c CONCLUSION Gene (codes for enzyme) Gene A Gene B Gene C Class II mutants Class III mutants (mutation in (mutation in gene B) gene C) Wild type Class I mutants (mutation in gene A) Precursor Precursor Precursor Precursor Enzyme A Enzyme A Enzyme A Enzyme A Ornithine Ornithine Ornithine Ornithine Enzyme B Enzyme B Enzyme B Enzyme B Citrulline Citrulline Citrulline Citrulline Enzyme C Enzyme C Enzyme C Enzyme C Arginine Arginine Arginine Arginine The Products of Gene Expression: A Developing Story • Some proteins aren’t enzymes, so researchers later revised the hypothesis: ______________ _____________________ • Many proteins are composed of several polypeptides, each of which has ____________ • Therefore, Beadle and Tatum’s hypothesis is now restated as the _____________________ ___________________ • Note that it is common to refer to gene products as ___________ rather than _______________ © 2011 Pearson Education, Inc. Basic Principles of Transcription and Translation • ____________ is the bridge between genes and the proteins for which they code • ___________________ is the synthesis of RNA using information in DNA • Transcription produces __________________ ________________ • __________________ is the synthesis of a polypeptide, using information in the mRNA • ________________ are the sites of translation © 2011 Pearson Education, Inc. • In prokaryotes, translation of mRNA can begin _____________________________________ • In a eukaryotic cell, the _____________________ separates transcription from translation • Eukaryotic RNA transcripts are modified through _________________ to yield the finished mRNA © 2011 Pearson Education, Inc. • A ____________________ is the initial RNA transcript from any gene prior to processing • The central dogma is the concept that cells are governed by a cellular chain of command: __________________________ © 2011 Pearson Education, Inc. Figure 17.UN01 DNA RNA Protein Figure 17.3a-2 TRANSCRIPTION DNA mRNA Ribosome TRANSLATION Polypeptide (a) Bacterial cell Figure 17.3b-3 Nuclear envelope TRANSCRIPTION RNA PROCESSING DNA Pre-mRNA mRNA TRANSLATION Ribosome Polypeptide (b) Eukaryotic cell The Genetic Code • How are the instructions for assembling amino acids into proteins encoded into DNA? • There are ________________, but there are only _____________________ in DNA • How many nucleotides correspond to an amino acid? © 2011 Pearson Education, Inc. Codons: Triplets of Nucleotides • The flow of information from gene to protein is based on a ___________________: a series of nonoverlapping, three-nucleotide words • The words of a gene are ___________________ into complementary nonoverlapping threenucleotide words of mRNA • These words are then ______________ into a chain of amino acids, forming a ______________ © 2011 Pearson Education, Inc. Figure 17.4 DNA template strand 5 3 A C C A A A C T T T G G T C G A G G G C T T C A 3 5 DNA molecule Gene 1 TRANSCRIPTION Gene 2 U G G mRNA U U U G G C U C A 5 3 Codon TRANSLATION Protein Trp Phe Gly Ser Gene 3 Amino acid • During transcription, one of the two DNA strands, called the _______________________, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript • The template strand is always the ____________ _____________________________ • During translation, the mRNA base triplets, called ____________, are read in the _______ direction © 2011 Pearson Education, Inc. • Codons along an mRNA molecule are read by translation machinery in the _________ direction • Each ________ specifies the _____________ (one of 20) to be placed at the corresponding position along a polypeptide © 2011 Pearson Education, Inc. Cracking the Code • All ________were deciphered by the mid-1960s • Of the 64 triplets, 61 code for ______________; 3 triplets are “_______” signals to end translation • The genetic code is ______________(more than one codon may specify a particular amino acid) but not ambiguous; no codon specifies more than one amino acid • Codons must be read in the correct ______ ___________(correct groupings) in order for the specified polypeptide to be produced © 2011 Pearson Education, Inc. Figure 17.5 Second mRNA base UUU U UUC First mRNA base (5 end of codon) UUA C Phe Leu UAU UCC UAC UCA Ser Tyr UGU UGC Cys U C UAA Stop UGA Stop A UCG UAG Stop UGG Trp G CUU CCU CAU CUC CCC CAC Leu CCA Pro CAA CUG CCG CAG AUU ACU AAU ACC AAC AUC Ile AUA AUG G UCU G UUG CUA A A C ACA Met or start Thr AAA His Gln Asn Lys CGU U CGC C CGA Arg CGG AGU G Ser AGC AGA A Arg U C A ACG AAG AGG G GUU GCU GAU GGU U GUC GCC GAC GGC C GAA GGA GUA GUG Val GCA GCG Ala GAG Asp Glu GGG Gly A G Third mRNA base (3 end of codon) U Evolution of the Genetic Code • The genetic code is _______________, shared by the simplest bacteria to the most complex animals • Genes can be transcribed and translated _____ ___________________from one species to another © 2011 Pearson Education, Inc. Figure 17.6 (a) Tobacco plant expressing a firefly gene (b) Pig expressing a jellyfish gene Concept 17.2: Transcription is the DNAdirected synthesis of RNA: a closer look • ____________is the first stage of gene expression © 2011 Pearson Education, Inc. Molecular Components of Transcription • RNA synthesis is catalyzed by _______________, which pries the DNA strands apart and hooks together the RNA nucleotides • The RNA is ______________to the DNA template strand • RNA synthesis follows the same base-pairing rules as DNA, except that __________substitutes for _________________ © 2011 Pearson Education, Inc. • The DNA sequence where RNA polymerase attaches is called the _______________; in bacteria, the sequence signaling the end of transcription is called the _______________ • The stretch of DNA that is transcribed is called a _______________________ © 2011 Pearson Education, Inc. Figure 17.7-4 Promoter Transcription unit 5 3 Start point RNA polymerase 3 5 DNA 1 Initiation Nontemplate strand of DNA 3 5 5 3 Unwound DNA RNA transcript Template strand of DNA 2 Elongation Rewound DNA 5 3 3 5 3 5 RNA transcript 3 Termination 3 5 5 3 5 Completed RNA transcript 3 Direction of transcription (“downstream”) Synthesis of an RNA Transcript • The three stages of transcription – ____________________ – ____________________ – ____________________ © 2011 Pearson Education, Inc. RNA Polymerase Binding and Initiation of Transcription • _______________ signal the transcriptional ___________ and usually extend several dozen nucleotide pairs upstream of the start point • _____________________ mediate the binding of RNA polymerase and the initiation of transcription • The completed assembly of transcription factors and _________________bound to a promoter is called a _______________________ • A promoter called a ______________is crucial in forming the initiation complex in eukaryotes © 2011 Pearson Education, Inc. Figure 17.8 1 A eukaryotic promoter Promoter Nontemplate strand DNA 5 3 3 5 T A T A A AA A T AT T T T TATA box Transcription factors Start point Template strand 2 Several transcription factors bind to DNA 5 3 3 5 3 Transcription initiation complex forms RNA polymerase II Transcription factors 5 3 5 3 RNA transcript Transcription initiation complex 3 5 Elongation of the RNA Strand • As __________________ moves along the DNA, it untwists the double helix, 10 to 20 bases at a time • Transcription progresses at a rate of ______ nucleotides per second in eukaryotes • A gene can be transcribed simultaneously by _______________________ • Nucleotides are added to the ________ of the growing RNA molecule © 2011 Pearson Education, Inc. Figure 17.9 Nontemplate strand of DNA RNA nucleotides RNA polymerase A 3 T C C A A 5 3 end C A U C C A T A G G T 5 5 C 3 T Direction of transcription Template strand of DNA Newly made RNA Termination of Transcription • The mechanisms of _________________ are different in bacteria and eukaryotes • In ________________, the polymerase stops transcription at the end of the _______________ and the mRNA can be translated without further modification • In ______________, RNA polymerase II transcribes the ___________________________; the RNA transcript is released ___________ nucleotides past this polyadenylation sequence © 2011 Pearson Education, Inc. Concept 17.3: Eukaryotic cells modify RNA after transcription • Enzymes in the eukaryotic nucleus modify premRNA (_______________) before the genetic messages are dispatched to the cytoplasm • During RNA processing, both ends of the primary transcript are usually ____________ • Also, usually some interior parts of the molecule are _______, and the other parts ____________ ____________________ © 2011 Pearson Education, Inc. Alteration of mRNA Ends • Each end of a pre-mRNA molecule is modified in a particular way – The 5 end receives a modified nucleotide _______ – The 3 end gets a _______________ • These modifications share several functions – They seem to facilitate the ________________ to the cytoplasm – They ______________from hydrolytic enzymes – They help ___________________to the 5 end © 2011 Pearson Education, Inc. Figure 17.10 5 G Protein-coding segment P P P 5 Cap 5 UTR Polyadenylation signal AAUAAA Start codon Stop codon 3 UTR 3 AAA … AAA Poly-A tail Split Genes and RNA Splicing • Most eukaryotic genes and their RNA transcripts have long ____________________of nucleotides that lie between coding regions • These noncoding regions are called intervening sequences, or ____________ • The other regions are called ____________ because they are eventually expressed, usually translated into amino acid sequences • _____________________removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence © 2011 Pearson Education, Inc. Figure 17.11 5 Exon Intron Exon Pre-mRNA 5 Cap Codon 130 31104 numbers Intron Exon 3 Poly-A tail 105 146 Introns cut out and exons spliced together mRNA 5 Cap Poly-A tail 1146 5 UTR Coding segment 3 UTR • In some cases, RNA splicing is carried out by ________________ • _________________ consist of a variety of proteins and several small _________________ _______________that recognize the splice sites © 2011 Pearson Education, Inc. Figure 17.12-3 RNA transcript (pre-mRNA) 5 Exon 1 Intron Protein snRNA Exon 2 Other proteins snRNPs Spliceosome 5 Spliceosome components 5 mRNA Exon 1 Exon 2 Cut-out intron Ribozymes • ______________ are catalytic RNA molecules that function as enzymes and can splice RNA • The discovery of ribozymes rendered ______________the belief that all biological catalysts were proteins © 2011 Pearson Education, Inc. • Three properties of RNA enable it to function as an enzyme – It can form a three-dimensional structure because of its ability to ___________________ – Some bases in RNA contain functional groups that may ________________________ – RNA may _______________________ with other nucleic acid molecules © 2011 Pearson Education, Inc. The Functional and Evolutionary Importance of Introns • Some introns contain sequences that may ________________________________ • Some genes can encode _________________ _________________, depending on which segments are treated as exons during splicing • This is called __________________________ • Consequently, the number of different proteins an organism can produce is ______________ than its number of genes © 2011 Pearson Education, Inc. • Proteins often have a modular architecture consisting of discrete regions called ________ • In many cases, _______________code for the different domains in a protein • __________________may result in the evolution of new proteins © 2011 Pearson Education, Inc. Figure 17.13 Gene DNA Exon 1 Intron Exon 2 Intron Exon 3 Transcription RNA processing Translation Domain 3 Domain 2 Domain 1 Polypeptide Concept 17.4: Translation is the RNAdirected synthesis of a polypeptide: a closer look • Genetic information flows from mRNA to protein through the process of __________________ © 2011 Pearson Education, Inc. Molecular Components of Translation • A cell translates an mRNA message into protein with the help of _________________________ • _____________ transfer amino acids to the growing polypeptide in a ribosome • ___________________ is a complex process in terms of its biochemistry and mechanics © 2011 Pearson Education, Inc. Figure 17.14 Amino acids Polypeptide Ribosome tRNA with amino acid attached tRNA C G Anticodon U G G U U U G G C 5 Codons mRNA 3 The Structure and Function of Transfer RNA • Molecules of tRNA are ________________ – Each carries a _________________ on one end – Each has an _________________ on the other end; the anticodon base-pairs with a complementary codon on mRNA © 2011 Pearson Education, Inc. • A tRNA molecule consists of a single RNA strand that is only about ____nucleotides long • Flattened into one plane to reveal its base pairing, a tRNA molecule looks like a ____________ © 2011 Pearson Education, Inc. Figure 17.15a 3 Amino acid attachment site 5 Hydrogen bonds Anticodon (a) Two-dimensional structure • Because of _______________, tRNA actually twists and folds into a three-dimensional molecule • tRNA is roughly ________________ © 2011 Pearson Education, Inc. Figure 17.15b Amino acid attachment site 5 3 Hydrogen bonds A A G 3 Anticodon (b) Three-dimensional structure 5 Anticodon (c) Symbol used in this book • Accurate translation requires two steps – First: a correct match between a tRNA and an amino acid, done by the enzyme _____________ ______________________ – Second: a correct match between the _______ _______________and an _________________ • Flexible pairing at the third base of a codon is called ______________and allows some tRNAs to bind to more than one codon © 2011 Pearson Education, Inc. Figure 17.16-4 Aminoacyl-tRNA synthetase (enzyme) Amino acid P Adenosine P P P Adenosine P Pi ATP Pi Pi tRNA Aminoacyl-tRNA synthetase tRNA Amino acid P Adenosine AMP Computer model Aminoacyl tRNA (“charged tRNA”) Ribosomes • _______________facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis • The __________ ribosomal subunits (large and small) are made of proteins and ______________ _____________________ • Bacterial and eukaryotic ribosomes are somewhat similar but have significant differences: some __________________specifically target bacterial ribosomes without harming eukaryotic ribosomes © 2011 Pearson Education, Inc. Figure 17.17a tRNA molecules Growing polypeptide Exit tunnel Large subunit E P A Small subunit 5 mRNA 3 (a) Computer model of functioning ribosome Figure 17.17b P site (Peptidyl-tRNA binding site) Exit tunnel A site (AminoacyltRNA binding site) E site (Exit site) E mRNA binding site P A Large subunit Small subunit (b) Schematic model showing binding sites Figure 17.17c Growing polypeptide Amino end Next amino acid to be added to polypeptide chain E tRNA mRNA 5 3 Codons (c) Schematic model with mRNA and tRNA • A ribosome has three binding sites for tRNA – The ___________holds the tRNA that carries the growing polypeptide chain – The ___________holds the tRNA that carries the next amino acid to be added to the chain – The ___________is the exit site, where discharged tRNAs leave the ribosome © 2011 Pearson Education, Inc. Building a Polypeptide • The three stages of translation – _______________ – _______________ – _______________ • All three stages require protein “__________” that aid in the translation process © 2011 Pearson Education, Inc. Ribosome Association and Initiation of Translation • The _______________of translation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits • First, a ________________binds with mRNA and a special initiator tRNA • Then the small subunit moves along the mRNA until it reaches the ________________________ • Proteins called ________________bring in the large subunit that completes the translation initiation complex © 2011 Pearson Education, Inc. Figure 17.18 Large ribosomal subunit 3 U A C 5 5 A U G 3 P site Pi Initiator tRNA GTP GDP E mRNA 5 Start codon mRNA binding site 3 Small ribosomal subunit 5 A 3 Translation initiation complex Elongation of the Polypeptide Chain • During the ______________, amino acids are added one by one to the preceding amino acid at the _______________of the growing chain • Each addition involves proteins called ______________________and occurs in three steps: _________________________________ _______________________________________ • Translation proceeds along the mRNA in a _____ __________ direction © 2011 Pearson Education, Inc. Figure 17.19-4 Amino end of polypeptide E 3 mRNA Ribosome ready for next aminoacyl tRNA P A site site 5 GTP GDP P i E E P A P A GDP P i GTP E P A Termination of Translation • Termination occurs when a ___________in the mRNA reaches the ___________of the ribosome • The A site accepts a protein called a _________ _______________ • The release factor causes the addition of a ___________molecule instead of an amino acid • This reaction releases the ______________, and the translation assembly then ____________ © 2011 Pearson Education, Inc. Figure 17.20-3 Release factor Free polypeptide 5 3 3 5 5 Stop codon (UAG, UAA, or UGA) 2 GTP 2 GDP 2 P i 3 Polyribosomes • A number of ribosomes can translate a single mRNA simultaneously, forming a _____________ (or _______________) • Polyribosomes enable a cell to make ___________ ______________of a polypeptide very quickly © 2011 Pearson Education, Inc. Figure 17.21 Growing polypeptides Completed polypeptide Incoming ribosomal subunits Start of mRNA (5 end) (a) End of mRNA (3 end) Ribosomes mRNA (b) 0.1 m Completing and Targeting the Functional Protein • Often translation is ___________________to make a functional protein • Polypeptide chains are ___________________or targeted to specific sites in the cell © 2011 Pearson Education, Inc. Protein Folding and Post-Translational Modifications • During and after synthesis, a polypeptide chain spontaneously ________________into its threedimensional shape • Proteins may also require ______________ ________________before doing their job • Some polypeptides are activated by _________ that cleave them • Other polypeptides come together to form the ______________of a protein © 2011 Pearson Education, Inc. Targeting Polypeptides to Specific Locations • Two populations of ribosomes are evident in cells: _____________ (in the cytosol) and ________ __________________(attached to the ER) • Free ribosomes mostly synthesize proteins that function in the ____________ • Bound ribosomes make proteins of the endomembrane system and proteins that are ________________________ • Ribosomes are ___________and can ___________ from free to bound © 2011 Pearson Education, Inc. • Polypeptide synthesis always begins in the ________________ • Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to ___________ _____________ • Polypeptides destined for the ER or for secretion are marked by a ________________ © 2011 Pearson Education, Inc. • A ________________binds to the signal peptide • The SRP brings the signal peptide and its ribosome to the _______ © 2011 Pearson Education, Inc. Figure 17.22 1 Ribosome 5 4 mRNA Signal peptide 3 SRP 2 ER LUMEN SRP receptor protein Translocation complex Signal peptide removed ER membrane Protein 6 CYTOSOL Concept 17.5: Mutations of one or a few nucleotides can affect protein structure and function • ________________ are changes in the genetic material of a cell or virus • ________________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 ____________________ © 2011 Pearson Education, Inc. Figure 17.23 Wild-type hemoglobin Sickle-cell hemoglobin Wild-type hemoglobin DNA C T T 3 5 G A A 5 3 Mutant hemoglobin DNA C A T 3 G T A 5 mRNA 5 5 3 mRNA G A A Normal hemoglobin Glu 3 5 G U A Sickle-cell hemoglobin Val 3 Types of Small-Scale Mutations • _______________within a gene can be divided into two general categories – ___________________ – One or more nucleotide-pair _______________ _______________ © 2011 Pearson Education, Inc. Substitutions • A _______________________replaces one nucleotide and its partner with another pair of nucleotides • __________________ have no effect on the amino acid produced by a codon because of redundancy in the genetic code • __________________ still code for an amino acid, but not the correct amino acid • __________________ change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein © 2011 Pearson Education, Inc. Figure 17.24a Wild type DNA template strand 3 T A C T T C A A A C C G A T T 5 5 A T G A A G T T G G C T T A A 3 mRNA5 A U G A A G U U U G G C U A A 3 Protein Met Lys Phe Gly Stop Amino end Carboxyl end (a) Nucleotide-pair substitution: silent A instead of G 3 T A C T T C A A A C C A A T T 5 5 A T G A A G T T T G G T T A A 3 U instead of C 5 A U G A A G U U U G G U U A A 3 Met Lys Phe Gly Stop Figure 17.24b Wild type DNA template strand 3 T A C T T C A A A C C G A T T 5 5 A T G A A G T T T G G C T A A 3 mRNA5 A U G A A G U U U G G C U A A 3 Protein Met Lys Phe Gly Stop Amino end Carboxyl end (a) Nucleotide-pair substitution: missense T instead of C 3 T A C T T C A A A T C G A T T 5 5 A T G A A G T T T A G C T A A 3 A instead of G 5 A U G A A G U U U A G C U A A 3 Met Lys Phe Ser Stop Figure 17.24c Wild type DNA template strand 3 T A C T T C A A A C C G A T T 5 5 A T G A A G T T T G G C T A A 3 mRNA5 A U G A A G U U U G G C U A A 3 Protein Met Lys Phe Gly Stop Amino end Carboxyl end (a) Nucleotide-pair substitution: nonsense A instead of T T instead of C 3 T A C A T C A A A C C G A T T 5 5 A T G T A G T T T G G C T A A 3 U instead of A 5 A U G U A G U U U G G C U A A 3 Met Stop Insertions and Deletions • ______________and ______________are additions or losses of nucleotide pairs in a gene • These mutations have a __________________on the resulting protein more often than substitutions do • Insertion or deletion of nucleotides may alter the reading frame, producing a __________________ © 2011 Pearson Education, Inc. Figure 17.24d Wild type DNA template strand 3 T A C T T C A A A C C G A T T 5 5 A T G A A G T T T G G C T A A 3 mRNA5 A U G A A G U U U G G C U A A 3 Protein Met Amino end Lys Phe Gly Stop Carboxyl end (b) Nucleotide-pair insertion or deletion: frameshift causing immediate nonsense Extra A 3 T A C A T T C A A A C G G A T T 5 5 A T G T A A G T T T G G C T A A 3 Extra U 5 A U G U A A G U U U G G C U A A 3 Met Stop 1 nucleotide-pair insertion Figure 17.24e Wild type DNA template strand 3 T A C T T C A A A C C G A T T 5 5 A T G A A G T T G G C T T A A 3 mRNA5 A U G A A G U U U G G C U A A 3 Protein Met Lys Phe Gly Amino end Stop Carboxyl end (b) Nucleotide-pair insertion or deletion: frameshift causing extensive missense A missing 3 T A C T T C A A C C G A T T 5 5 A T G A A G T T G G C T A A 3 U missing 5 A U G A A G U U G G C U A A Met Lys 1 nucleotide-pair deletion Leu Ala 3 Figure 17.24f Wild type DNA template strand 3 T A C T T C A A A C C G A T T 5 5 A T G A A G T T T G G C T A A 3 mRNA5 A U G A A G U U U G G C U A A 3 Protein Met Gly Lys Phe Stop Carboxyl end Amino end (b) Nucleotide-pair insertion or deletion: no frameshift, but one amino acid missing T T C missing 3 T A C 5 A T G A A A C C G A T T 5 T T T G G C T A A 3 A A G missing 5 A U G Met U U U G G C U A A 3 Phe 3 nucleotide-pair deletion Gly Stop Mutagens • ________________ can occur during DNA replication, recombination, or repair • _________________are physical or chemical agents that can cause mutations © 2011 Pearson Education, Inc. Concept 17.6: While gene expression differs among the domains of life, the concept of a gene is universal • _____________________, but share many features of gene expression with eukaryotes © 2011 Pearson Education, Inc. Comparing Gene Expression in Bacteria, Archaea, and Eukarya • Bacteria and eukarya differ in their RNA polymerases, termination of transcription, and ribosomes; ____________ tend to resemble eukarya in these respects • Bacteria can ________________transcribe and translate the same gene • In eukarya, transcription and translation are separated by the _________________ • In archaea, transcription and translation are likely ______________ © 2011 Pearson Education, Inc. Figure 17.25 RNA polymerase DNA mRNA Polyribosome RNA polymerase Direction of transcription 0.25 m DNA Polyribosome Polypeptide (amino end) Ribosome mRNA (5 end) What Is a Gene? Revisiting the Question • The idea of the gene has ______________ through the history of genetics • We have considered a gene as – A discrete unit of __________________ – A region of _________________in a chromosome – A DNA sequence that codes for a ___________________________________ © 2011 Pearson Education, Inc. Figure 17.26 DNA TRANSCRIPTION 3 5 RNA polymerase RNA transcript Exon RNA PROCESSING RNA transcript (pre-mRNA) AminoacyltRNA synthetase Intron NUCLEUS Amino acid AMINO ACID ACTIVATION tRNA CYTOPLASM mRNA Growing polypeptide 3 A Aminoacyl (charged) tRNA P E Ribosomal subunits TRANSLATION E A Anticodon Codon Ribosome • In summary, a ___________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 © 2011 Pearson Education, Inc.