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Chapter 9 • Gene Expression and Regulation Copyright © 2006 Pearson Prentice Hall, Inc. 9.1 How Is the Information in DNA Used in a Cell? • 9.1.1 Most Genes Contain Information for the Synthesis of a Single Protein • 9.1.2 RNA Intermediaries Carry the Genetic Information for Protein Synthesis – Table 9.1 A Comparison of DNA and RNA (p. 126) Copyright © 2006 Pearson Prentice Hall, Inc. Copyright © 2006 Pearson Prentice Hall, Inc. 9.1 How Is the Information in DNA Used in a Cell? • 9.1.3 Overview: Genetic Information Is Transcribed into RNA, Then Translated into Protein – Figure 9.1 Genetic information flows from DNA to RNA to protein (p. 126) Copyright © 2006 Pearson Prentice Hall, Inc. gene DNA (nucleus) (cytoplasm) (a) Transcription messenger RNA (b) Translation ribosome protein Copyright © 2006 Pearson Prentice Hall, Inc. 9.2 What Is the Genetic Code? • 9.2.1 A Sequence of Three Bases Codes for an Amino Acid – Table 9.2 The Genetic Code (Codons of mRNA) (p. 127) Copyright © 2006 Pearson Prentice Hall, Inc. Copyright © 2006 Pearson Prentice Hall, Inc. 9.3 How Is the Information in a Gene Transcribed into RNA? • 9.3.1 Transcription Begins When RNA Polymerase Binds to the Promoter of a Gene – Figure 9.2 Transcription is the synthesis of RNA from instructions in DNA (p. 128) Copyright © 2006 Pearson Prentice Hall, Inc. DNA gene 1 gene 2 gene 3 Initiation DNA RNA polymerase promote r RNA polymerase binds to the promoter region of DNA near the beginning of a gene, separating the double helix near the promoter. Elongation RNA DNA template strand RNA polymerase travels along the DNA template strand, catalyzing the addition of ribose nucleotides into an RNA molecule. The nucleotides in the RNA are complementary to the template strand of the DNA. Termination termination signal At the end of a gene, RNA polymerase encounters a sequence of DNA called a termination signal. RNA polymerase detaches from the DNA and releases the RNA molecule. Conclusion of transcription RNA After termination, the DNA completely rewinds into a double helix. The RNA molecule is free to move from the nucleus to the cytoplasm for translation, and RNA polymerase may move to another gene and begin transcription once again. Copyright © 2006 Pearson Prentice Hall, Inc. DNA gene 1 gene 2 gene 3 Initiation DNA RNA polymerase promoter RNA polymerase binds to the promoter region of DNA near the beginning of a gene, separating the double helix near the promoter. Copyright © 2006 Pearson Prentice Hall, Inc. Elongation RNA DNA template strand RNA polymerase travels along the DNA template strand, catalyzing the addition of ribose nucleotides into an RNA molecule. The nucleotides in the RNA are complementary to the template strand of the DNA. Copyright © 2006 Pearson Prentice Hall, Inc. Termination termination signal At the end of a gene, RNA polymerase encounters a sequence of DNA called a termination signal. RNA polymerase detaches from the DNA and releases the RNA molecule. Copyright © 2006 Pearson Prentice Hall, Inc. Conclusion of transcription RNA After termination, the DNA completely rewinds into a double helix. The RNA molecule is free to move from the nucleus to the cytoplasm for translation, and RNA polymerase may move to another gene and begin transcription once again. Copyright © 2006 Pearson Prentice Hall, Inc. 9.3 How Is the Information in a Gene Transcribed into RNA? • 9.3.2 Elongation Generates a Growing Strand of RNA – Figure 9.3 RNA transcription in action (p. 129) Copyright © 2006 Pearson Prentice Hall, Inc. RNA transcription gene RNA molecules DNA Copyright © 2006 Pearson Prentice Hall, Inc. 9.3 How Is the Information in a Gene Transcribed into RNA? • 9.3.3 Transcription Stops When RNA Polymerase Reaches the Termination Signal • 9.3.4 Transcription Is Selective Copyright © 2006 Pearson Prentice Hall, Inc. 9.4 What Are the Functions of RNA? • Figure 9.4 Cells synthesize three major types of RNA (p. 130) Copyright © 2006 Pearson Prentice Hall, Inc. Messenger RNA (mRNA) Ribosome: contains ribosomal RNA (rRNA) large subunit catalytic site tRNA/amino acid binding sites small subunit Transfer RNA (tRNA) tyr attached amino acid anticodon Copyright © 2006 Pearson Prentice Hall, Inc. Messenger RNA (mRNA) Copyright © 2006 Pearson Prentice Hall, Inc. Ribosome: contains ribosomal RNA (rRNA) large subunit small subunit Copyright © 2006 Pearson Prentice Hall, Inc. catalytic site tRNA/amino acid binding sites Transfer RNA (tRNA) tyr attached amino acid anticodon Copyright © 2006 Pearson Prentice Hall, Inc. 9.4 What Are the Functions of RNA? • 9.4.1 Messenger RNA Carries the Code for a Protein from the Nucleus to the Cytoplasm • 9.4.2 Ribosomal RNA and Proteins Form Ribosomes • 9.4.3 Transfer RNA Molecules Carry Amino Acids to the Ribosomes Copyright © 2006 Pearson Prentice Hall, Inc. 9.5 How Is the Information in Messenger RNA Translated into Protein? • 9.5.1 Translation Begins When tRNA and mRNA Bind to a Ribosome – Figure 9.5 Translation is the process of protein synthesis (p. 132) Copyright © 2006 Pearson Prentice Hall, Inc. Initiation: amino acid second tRNA binding site catalytic site met met tRNA initiation complex methionine tRNA mRNA large ribosomal subunit first tRNA binding site small ribosomal subunit A tRNA with an attached methionine amino acid binds to a small ribosomal subunit, forming an initiation complex. The initiation complex binds to an mRNA molecule. The methionine (met) tRNA anticodon (UAC) basepairs with the start codon (AUG) of the mRNA. The large ribosomal subunit binds to the small subunit. The methionine tRNA binds to the first tRNA site on the large subunit. Elongation: catalytic site The second codon of mRNA (GUU) base-pairs with the anticodon (CAA) of a second tRNA carrying the amino acid valine (val). This tRNA binds to the second tRNA site on the large subunit. catalytic site initiator peptide tRNA detaches bond The catalytic site on the large subunit catalyzes the formation of a peptide bond linking the amino acids methionine and valine. The two amino acids are now attached to the tRNA in the second binding position. ribosome moves one codon to right The "empty" tRNA is released and the ribosome moves down the mRNA, one codon to the right. The tRNA that is attached to the two amino acids is now in the first tRNA binding site and the second tRNA binding site is empty. Termination: catalytic site completed peptide stop codon The third codon of mRNA (CAU) base-pairs with the anticodon (GUA) of a tRNA carrying the amino acid histidine (his). This tRNA enters the second tRNA binding site on the large subunit. The catalytic site forms a new peptide bond between valine and histidine. A three-aminoacid chain is now attached to the tRNA in the second binding site. The tRNA in the first site leaves, and the ribosome moves one codon over on the mRNA. Copyright © 2006 Pearson Prentice Hall, Inc. This process repeats until a stop codon is reached; the mRNA and the completed peptide are released from the ribosome, and the subunits separate. Initiation: amino acid met met catalytic site second tRNA binding site tRNA initiation complex methionine tRNA mRNA first tRNA binding site large ribosomal subunit small ribosomal subunit A tRNA with an attached methionine amino acid binds to a small ribosomal subunit, forming an initiation complex. The initiation complex binds to an mRNA molecule. The methionine (met) tRNA anticodon (UAC) basepairs with the start codon (AUG) of the mRNA. Copyright © 2006 Pearson Prentice Hall, Inc. The large ribosomal subunit binds to the small subunit. The methionine tRNA binds to the first tRNA site on the large subunit. amino acid met methionine tRNA initiation complex small ribosomal subunit A tRNA with an attached methionine amino acid binds to a small ribosomal subunit, forming an initiation complex. Copyright © 2006 Pearson Prentice Hall, Inc. met tRNA mRNA The initiation complex binds to an mRNA molecule. The methionine (met) tRNA anticodon (UAC) basepairs with the start codon (AUG) of the mRNA. Copyright © 2006 Pearson Prentice Hall, Inc. catalytic site first tRNA binding site second tRNA binding site large ribosomal subunit The large ribosomal subunit binds to the small subunit. The methionine tRNA binds to the first tRNA site on the large subunit. Copyright © 2006 Pearson Prentice Hall, Inc. Elongation: catalytic site catalytic site peptide bond initiator tRNA detaches ribosome moves one codon to right The second codon of mRNA (GUU) base-pairs with the anticodon (CAA) of a second tRNA carrying the amino acid valine (val). This tRNA binds to the second tRNA site on the large subunit. The catalytic site on the large subunit catalyzes the formation of a peptide bond linking the amino acids methionine and valine. The two amino acids are now attached to the tRNA in the second binding position. Copyright © 2006 Pearson Prentice Hall, Inc. The "empty" tRNA is released and the ribosome moves down the mRNA, one codon to the right. The tRNA that is attached to the two amino acids is now in the first tRNA binding site and the second tRNA binding site is empty. catalytic site The second codon of mRNA (GUU) base-pairs with the anticodon (CAA) of a second tRNA carrying the amino acid valine (val). This tRNA binds to the second tRNA site on the large subunit. Copyright © 2006 Pearson Prentice Hall, Inc. peptide bond The catalytic site on the large subunit catalyzes the formation of a peptide bond linking the amino acids methionine and valine. The two amino acids are now attached to the tRNA in the second binding position. Copyright © 2006 Pearson Prentice Hall, Inc. catalytic site initiator tRNA detaches ribosome moves one codon to right The "empty" tRNA is released and the ribosome moves down the mRNA, one codon to the right. The tRNA that is attached to the two amino acids is now in the first tRNA binding site and the second tRNA binding site is empty. Copyright © 2006 Pearson Prentice Hall, Inc. Termination: catalytic site completed peptide stop codon The third codon of mRNA (CAU) base-pairs with the anticodon (GUA) of a tRNA carrying the amino acid histidine (his). This tRNA enters the second tRNA binding site on the large subunit. The catalytic site forms a new peptide bond between valine and histidine. A three-aminoacid chain is now attached to the tRNA in the second binding site. The tRNA in the first site leaves, and the ribosome moves one codon over on the mRNA. Copyright © 2006 Pearson Prentice Hall, Inc. This process repeats until a stop codon is reached; the mRNA and the completed peptide are released from the ribosome, and the subunits separate. catalytic site The third codon of mRNA (CAU) base-pairs with the anticodon (GUA) of a tRNA carrying the amino acid histidine (his). This tRNA enters the second tRNA binding site on the large subunit. Copyright © 2006 Pearson Prentice Hall, Inc. The catalytic site forms a new peptide bond between valine and histidine. A three-aminoacid chain is now attached to the tRNA in the second binding site. The tRNA in the first site leaves, and the ribosome moves one codon over on the mRNA. Copyright © 2006 Pearson Prentice Hall, Inc. completed peptide stop codon This process repeats until a stop codon is reached; the mRNA and the completed peptide are released from the ribosome, and the subunits separate. Copyright © 2006 Pearson Prentice Hall, Inc. 9.5 How Is the Information in Messenger RNA Translated into Protein? • 9.5.2 Elongation Generates a Growing Chain of Amino Acids • 9.5.3 A Stop Codon Signals Termination – Figure 9.6 Complementary base pairing is critical to decoding genetic information (p. 133) Copyright © 2006 Pearson Prentice Hall, Inc. gene DNA etc. complementary DNA strand template DNA strand etc. codons mRNA etc. anticodons tRNA etc. amino acids protein methionine Copyright © 2006 Pearson Prentice Hall, Inc. glycine valine etc. gene DNA complementary DNA strand template DNA strand Copyright © 2006 Pearson Prentice Hall, Inc. etc. etc. codons mRNA Copyright © 2006 Pearson Prentice Hall, Inc. etc. tRNA Copyright © 2006 Pearson Prentice Hall, Inc. etc. amino acids protein methionine Copyright © 2006 Pearson Prentice Hall, Inc. glycine valine etc.