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CHAPTER 10 Molecular Biology of the Gene

CHAPTER 10 Molecular Biology of the Gene. Modules 10.1 – 10.5. Saboteurs Inside Our Cells. The invasion and damage of cells by the herpesvirus can be compared to the actions of a saboteur intent on taking over a factory

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CHAPTER 10 Molecular Biology of the Gene

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  1. CHAPTER 10Molecular Biology of the Gene Modules 10.1 – 10.5

  2. Saboteurs Inside Our Cells • The invasion and damage of cells by the herpesvirus can be compared to the actions of a saboteur intent on taking over a factory • The herpesvirus hijacks the host cell’s molecules and organelles to produce new copies of the virus

  3. Viruses provided some of the earliest evidence that genes are made of DNA • Molecular biology studies how DNA serves as the molecular basis of heredity

  4. THE STRUCTURE OF THE GENETIC MATERIAL 10.1 Experiments showed that DNA is the genetic material • The Hershey-Chase experiment showed that certain viruses reprogram host cells to produce more viruses by injecting their DNA Head DNA Tail Tailfiber Figure 10.1A

  5. Agitate in a blender to separate phages outside the bacteria from the cells and their contents. Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. Measure the radioactivity in the pellet and liquid. Mix radioactivelylabeled phages with bacteria. The phages infect the bacterial cells. 1 2 3 4 • The Hershey-Chase Experiment Radioactiveprotein Emptyprotein shell Radioactivityin liquid Phage Bacterium PhageDNA DNA Batch 1Radioactiveprotein Centrifuge Pellet RadioactiveDNA Batch 2RadioactiveDNA Centrifuge Radioactivityin pellet Pellet Figure 10.1B

  6. Phage reproductive cycle Phage attaches to bacterial cell. Phage injects DNA. Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble. Cell lyses and releases new phages. Figure 10.1C

  7. 10.2 DNA and RNA are polymers of nucleotides • DNA is a nucleic acid, made of long chains of nucleotides Phosphate group Nitrogenous base Nitrogenous base(A, G, C, or T) Sugar Phosphategroup Nucleotide Thymine (T) Sugar(deoxyribose) DNA nucleotide Figure 10.2A Polynucleotide Sugar-phosphate backbone

  8. DNA has four kinds of bases, A, T, C, and G Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines Purines Figure 10.2B

  9. RNA has a slightly different sugar • RNA has U instead of T • RNA is also a nucleic acid Nitrogenous base(A, G, C, or U) Phosphategroup Uracil (U) Sugar(ribose) Figure 10.2C, D

  10. 10.3 DNA is a double-stranded helix • James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B

  11. The structure of DNA consists of two polynucleotide strands wrapped around each other in a double helix 1 chocolate coat, Blind (PRA) Figure 10.3C Twist

  12. Each base pairs with a complementary partner • A pairs with T • G pairs with C • Hydrogen bonds between bases hold the strands together

  13. Hydrogen bond • Three representations of DNA Ribbon model Partial chemical structure Computer model Figure 10.3D

  14. DNA REPLICATION 10.4 DNA replication depends on specific base pairing • In DNA replication, the strands separate • Enzymes use each strand as a template to assemble the new strands A A Nucleotides Parental moleculeof DNA Both parental strands serveas templates Two identical daughtermolecules of DNA Figure 10.4A

  15. Untwisting and replication of DNA Figure 10.4B

  16. 10.5 DNA replication: A closer look • DNA replication begins at specific sites Parental strand Origin of replication Daughter strand Bubble Two daughter DNA molecules Figure 10.5A

  17. 5 end 3 end P • Each strand of the double helix is oriented in the opposite direction P P P P P P P 3 end 5 end Figure 10.5B

  18. 3 DNA polymerasemolecule 5 5 end Daughter strandsynthesizedcontinuously Parental DNA 5 3 Daughter strandsynthesizedin pieces • How DNA daughter strands are synthesized 3 P 5 • The daughter strands are identical to the parent molecule 5 P 3 DNA ligase Overall direction of replication Figure 10.5C

  19. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN 10.6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits • The information constituting an organism’s genotype is carried in its sequence of bases

  20. The DNA is transcribed into RNA, which is translated into the polypeptide • A specific gene specifies a polypeptide DNA TRANSCRIPTION DNA TRANSLATION Protein Figure 10.6A

  21. Studies of the bread mold Neurospora crassa led to the one gene-one polypeptide hypothesis • Studies of inherited metabolic disorders first suggested that phenotype is expressed through proteins Figure 10.6B

  22. 10.7 Genetic information written in codons is translated into amino acid sequences • The “words” of the DNA “language” are triplets of bases called codons • The codons in a gene specify the amino acid sequence of a polypeptide

  23. Gene 1 Gene 3 DNA molecule Gene 2 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Amino acid Figure 10.7

  24. 10.8 The genetic code is the Rosetta stone of life • Virtually all organisms share the same genetic code Figure 10.8A

  25. Transcribed strand • An exercise in translating the genetic code DNA Transcription RNA Startcodon Stopcodon Translation Polypeptide Figure 10.8B

  26. 10.9 Transcription produces genetic messages in the form of RNA RNA nucleotide RNApolymerase Direction oftranscription Templatestrand of DNA Newly made RNA Figure 10.9A

  27. RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation • RNA nucleotides line up along one strand of the DNA following the base-pairing rules • The single-stranded messenger RNA peels away and the DNA strands rejoin • In transcription, the DNA helix unzips Elongation Area shownin Figure 10.9A Termination GrowingRNA Completed RNA RNApolymerase Figure 10.9B

  28. 10.10 Eukaryotic RNA is processed before leaving the nucleus Exon Intron Exon Intron Exon DNA TranscriptionAddition of cap and tail • Noncoding segments called introns are spliced out • A cap and a tail are added to the ends Cap RNAtranscriptwith capand tail Introns removed Tail Exons spliced together mRNA Coding sequence NUCLEUS CYTOPLASM Figure 10.10

  29. 10.11 Transfer RNA molecules serve as interpreters during translation Amino acid attachment site • In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide • The process is aided by transfer RNAs Hydrogen bond RNA polynucleotide chain Anticodon Figure 10.11A

  30. Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other Amino acidattachment site Anticodon Figure 10.11B, C

  31. 10.12 Ribosomes build polypeptides Next amino acidto be added topolypeptide Growingpolypeptide tRNA molecules P site A site Growingpolypeptide Largesubunit tRNA P A mRNA mRNAbindingsite Codons mRNA Smallsubunit Figure 10.12A-C

  32. 10.13 An initiation codon marks the start of an mRNA message Start of genetic message End Figure 10.13A

  33. mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Largeribosomalsubunit Initiator tRNA P site A site Startcodon Small ribosomalsubunit mRNA 1 2 Figure 10.13B

  34. 10.14 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation • The mRNA moves a codon at a time relative to the ribosome • A tRNA pairs with each codon, adding an amino acid to the growing polypeptide

  35. Amino acid Polypeptide Asite P site Anticodon mRNA 1 Codon recognition mRNAmovement Stopcodon Newpeptidebond 2 Peptide bond formation 3 Translocation Figure 10.14

  36. 10.15 Review: The flow of genetic information in the cell is DNARNAprotein • The sequence of codons in DNA spells out the primary structure of a polypeptide • Polypeptides form proteins that cells and organisms use

  37. TRANSCRIPTION DNA Stage mRNA istranscribed from aDNA template. 1 mRNA RNApolymerase • Summary of transcription and translation Amino acid TRANSLATION Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 2 Enzyme tRNA Initiator tRNA Anticodon Stage Initiation of polypeptide synthesis 3 Largeribosomalsubunit The mRNA, the first tRNA, and the ribosomal subunits come together. Start Codon Smallribosomalsubunit mRNA Figure 10.15

  38. Newpeptidebondforming Growing polypeptide Stage Elongation 4 A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. Codons mRNA Polypeptide Stage Termination 5 The ribosome recognizes a stop codon. The poly-peptide is terminated and released. Stop Codon Figure 10.15 (continued)

  39. 10.16 Mutations can change the meaning of genes • Mutations are changes in the DNA base sequence • These are caused by errors in DNA replication or by mutagens • The change of a single DNA nucleotide causes sickle-cell disease

  40. Normal hemoglobin DNA Mutant hemoglobin DNA mRNA mRNA Normal hemoglobin Sickle-cell hemoglobin Glu Val Figure 10.16A

  41. NORMAL GENE • Types of mutations mRNA Protein Met Lys Phe Gly Ala BASE SUBSTITUTION Met Lys Phe Ser Ala Missing BASE DELETION Met Lys Leu Ala His Figure 10.16B

  42. VIRUSES: GENES IN PACKAGES 10.17 Viral DNA may become part of the host chromosome Phage Attachesto cell Bacterialchromosome Phage DNA Cell lyses,releasing phages Phage injects DNA Many celldivisions Occasionally a prophagemay leave the bacterialchromosome LYTIC CYCLE LYSOGENIC CYCLE Phagesassemble Phage DNAcircularizes Lysogenic bacteriumreproduces normally,replicating the prophageat each cell division Prophage OR New phage DNA andproteins are synthesized Phage DNA inserts into the bacterialchromosome by recombination

  43. 10.18 Connection: Many viruses cause disease in animals Membranousenvelope • Many viruses have RNA, rather than DNA, as their genetic material • Example: flu viruses RNA Proteincoat Glycoprotein spike Figure 10.18A

  44. Glycoprotein spike VIRUS Protein coat Viral RNA(genome) Envelope Plasmamembraneof hostcell Entry 1 Uncoating 2 • Some animal viruses steal a bit of the host cell’s membrane Viral RNA(genome) RNA synthesisby viral enzyme 3 Proteinsynthesis RNA synthesis(other strand) 5 4 mRNA Template New viral genome Newviral protein Newviral proteins Assembly 6 Exit 7 Figure 10.18B

  45. 10.19 Connection: Plant viruses are serious agricultural pests • Most plant viruses have RNA • Example: tobacco mosaic disease Protein RNA Figure 10.19

  46. 10.20 Connection: Emerging viruses threaten human health • The deadly Ebola virus causes hemorrhagic fever • Each virus is an enveloped thread of protein-coated RNA • Hantavirus is another enveloped RNA virus Figure 10.20A, B

  47. 10.21 The AIDS virus makes DNA on an RNA template • HIV is a retrovirus Envelope Glycoprotein Proteincoat RNA(two identicalstrands) Reversetranscriptase Figure 10.21A

  48. Viral RNA CYTOPLASM 1 NUCLEUS • Inside a cell, HIV uses its RNA as a template for making DNA to insert into the host chromosome DNAstrand ChromosomalDNA 2 3 ProvirusDNA Double-strandedDNA 4 5 RNA ViralRNAandproteins 6 Figure 10.21B

  49. 10.22 Virus research and molecular genetics are intertwined • Virus studies help establish molecular genetics • Molecular genetics helps us understand viruses • such as HIV, seen here attacking a white blood cell Figure 10.22

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