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Honors Bio - Chapter 10

Honors Bio - Chapter 10. 0. Molecular Biology of the Gene. Viruses - infect cells - Gave us some of the earliest evidence that genes are made of DNA. 10.1 Experiments showed DNA was the genetic material. Frederick Griffith 1928 Tried to make a vaccine for pneumonia

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Honors Bio - Chapter 10

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  1. Honors Bio - Chapter 10 0 Molecular Biology of the Gene

  2. Viruses - infect cells - Gave us some of the earliest evidence that genes are made of DNA

  3. 10.1 Experiments showed DNA was the genetic material • Frederick Griffith 1928 • Tried to make a vaccine for pneumonia • Used mice and two strains of bacteria: • - one harmless (“R type”) • - one pathogenic (“S type”) • Live R alone and dead S alone did not cause immune response • Mixed live R with dead S

  4. Live R (‘rough’)  no disease Live S (‘smooth’)  pneumonia Mix Live R and dead S  pneumonia

  5. What happened to Griffith’s mice? • Mice treated with live R and dead S • - got sick and died • - had live type S bacteria in them! • Where did the live S come from? • Griffith’s Conclusion: Something from dead S cells transformed live R cells into live S

  6. Griffith’s conclusion • Something from dead S cells transformed living R cells into living S cells

  7. Avery, McLeod, and McCartey Problem: What substance from dead S transformed live R into live S? Experiment: Grow live R and dead S in cultures - each culture has a different enzyme which destroys one type of molecule - carbs, lipids, proteins, RNA, or DNA - Which enzyme stops transformation?

  8. Only bacteria grown in DNAase did not transform Conclusion: DNA is the transforming material

  9. The Hershey-Chase experiment 1952 • Background: Viruses change host cells - produce more virus • Problem: Is it the protein coat? Or the DNA? • Experiment: grow bacteria in culture, add phage virus tagged with radioactive isotope • - use sulfur  proteins (capsid) are radioactive • - use phosphorus  phage DNA is radioactive • Let phage infect bacteria – where is radioactivity?

  10. Hershey-Chase Experiment Grow bacteria in culture with tagged phage. Virus infects bacteria Blender shakes phage loose from bacterial cells. Is radioactivity in the liquid (phage), or in the cells (bacteria)? Centrifuge separates cells from culture liquid

  11. Hershey-Chase Results • Phage tagged with phosphorus  bacterial cells became radioactive • Conclusion: phage DNA entered cells, but protein did not

  12. Bacteriophage Figure 10.1A Virus Life Cycle

  13. 10.3 Finding the structure of DNA Rosalind Franklin’s X-ray picture of DNA crystal shows double helix Watson & Crick, 1953

  14. Sugar-phosphate backbone Phosphate group Nitrogenous base A A Sugar Nitrogenous base(A, G, C, or T) Phosphategroup C C DNA nucleotide O H H3C C C N O C C T CH2 H T O P N O O O– Thymine (T) O C C H H H H G G C C H O Sugar(deoxyribose) T T DNA nucleotide DNA polynucleotide • 10.2 DNA and RNA are polymers of nucleotides Figure 10.2A

  15. H H H H O N N O C H C H H3C C C H N N N C C N C N N C H H C C C C C C C C C C H O H N N N O H N N H N N H H H H H Adenine (A) Guanine (G) Thymine (T) Cytosine (C) Purines Pyrimidines DNA has four kinds of nitrogen bases Purines have two nitrogen-carbon rings (A and G) Pyrimidines have one ring (T and C) Figure 10.2B

  16. Nitrogenous base (A, G, C, or U) O Phosphategroup C H H N C O C C H O P O CH2 O N Uracil (U) O– O C C H H H H C C OH O Sugar(ribose) RNA is also a nucleic acid • Has ribose sugar • Has uracilinstead of thymine base 3 kinds of RNA Figure 10.2C

  17. Three kinds of RNA Messenger RNA (mRNA) – carries code from DNA in nucleus to ribosome Ribosomal RNA (rRNA) – makes up ribosome, along with proteins Transfer RNA (tRNA) – carries one amino acid to ribosome and matches to mRNA code

  18. Twist The structure of DNA • Two polynucleotide strands double helix Figure 10.3C

  19. Hydrogen bonds hold two strands together G C O T A OH P Hydrogen bond –O O A T OH O H2C A T Basepair O CH2 O O C G P O O– –O C G O P O H2C O O C T G A O CH2 C G O O P O O– – O O P O H2C O O G C A T O CH2 O O A T P O – O O– O P A T O O H2C O A T A T CH2 O OH O O– P G C HO O T A Partial chemical structure Ribbon model Computer model • Form between complementary bases • A with T (2 H bonds), and G with C (3 H bonds) Figure 10.3D

  20. T A T T A A T A T A G C G G G C C C G C C C G G G C G C C A A T A T A A T T A T T T A A A T Both parental strands serve as templates Two identical daughtermolecules of DNA Parental moleculeof DNA 10.4 DNA REPLICATION • 10.4 Depends on specific base pairing • Starts with the separation of DNA strands • Then enzymes use each strand as a template • Assemble new nucleotides into complementary strands Nucleotides Figure 10.4A

  21. DNA replication: • For cell division • Starts in several places at once • Each original strand is template for a new strand (“semi-conservative” • Proceeds until entire strands are duplicated • Copies stay together at centromere

  22. Parental strand Origin of replication Daughter strand Bubble Two daughter DNA molecules • 10.5 Replication begins at several sites (origins) • “bubbles” elongate and merge Figure 10.5A

  23. DNA strands are antiparallel 5 end 3 end P HO 5 4 2 3 A T 3 1 1 4 2 5 P P C G P P G C P P A T OH P 3 end 5 end Go in opposite directions DNA works in only one direction -- from 5’ to 3’ Figure 10.5B

  24. DNA polymerase molecule 3 5 Daughter strandsynthesizedcontinuously Parental DNA 5 3 Daughter strandsynthesizedin pieces 3 5 5 3 DNA ligase Overall direction of replication • Enzyme DNA polymerase • Leading Strand: one daughter strand synthesized as a continuous piece • Lagging strand: other strand a series of short pieces, joined by enzyme DNA ligase Leading and lagging strands Figure 10.5C

  25. Gene Expression = Protein Synthesis Gene info – From DNA to RNA to protein 10.6 The DNA genotype is expressed as proteins, which are the molecular basis for phenotypic traits • Information in an organism’s genotype • Is carried in the sequence of its DNA bases • A particular gene (linear sequence of many nucleotides) has code for one polypeptide

  26. Two stages in gene expression DNA Transcription RNA Translation Protein Figure 10.6A • DNA of agene is transcribed into RNA • RNA is then translated into the polypeptide

  27. RNA nucleotides RNA polymerase A C C A T T A U T C T G U G A C A U C C A C C A G A T T T A G G Direction of transcription Template Strand of DNA Newly made RNA Stage 1: Transcription – in nucleus • mRNA synthesis - writes the gene onto a messenger molecule ONE gene on one side of DNA is copied DNA unzips mRNA leaves nucleus

  28. Helicase enzyme unwinds part of DNA • RNA nucleotides line up along one strand of the DNA, following the base pairing rules • RNA polymerase joins nucleotides • Single-stranded messenger RNA (mRNA) forms • Finished RNA detaches from DNA • DNA strands rejoin and rewind

  29. RNA polymerase DNA of gene Promoter DNA Terminator DNA Area shown In Figure 10.9A Growing RNA Completed RNA RNA polymerase Figure 10.9B Transcription of a gene 1 Initiation 2 Elongation 3 Termination

  30. Transcription – writes DNA code onto mRNA

  31. Exon Intron Exon Intron Exon DNA Transcription Addition of cap and tail Cap RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm Figure 10.10 RNA processing • Before leaving nucleus • Noncoding segments (introns)are spliced out • And a cap and a tail are added to the ends

  32. The DNA “code” • 10.7 Genetic information is written in three-base sets called codons” • A codon specifies one amino acid • Sequence of codons = sequence of amino acids • Primary structure of a protein

  33. DNA molecule Gene 1 Gene 2 Gene 3 DNA strand A A A C A C G G A A C A Transcription U U U G U G C C U U G U RNA Codon Translation Polypeptide Amino acid Figure 10.7

  34. Second base U C A G U UAU UGU UGC UGA Stop UUU UCU Cys Phe Tyr UUC UAC C UCC Ser U UCA UUA UAA Stop A Leu UCG UAG Stop UGG Trp G U CAU CGU CUU CCU His C CAC CGC CUC CCC C Pro Arg Leu CUA CCA CAA CGA A Gln CAG CGG CUG CCG G Third base First base U ACU AUU AAU AGU Ser Asn ACC AGC AUC AAC Ile C A Thr AUA AGA ACA AAA A Lys Arg Met or start ACC AGG AAG AUG G U GUU GAU GGU GCU Asp C GGC GCC GUC GAC Gly Ala G Val GUA GCA GGA GAA A Glu GUG GCG GGG GAG G Figure 10.8A All organisms use the same code UUG

  35. All organisms use the same code UUG

  36. Strand to be transcribed T A C T T C A A A A T C DNA A T G A A G T T T T A G Transcription G U U U A G A U A A G U RNA Startcondon Stopcondon Translation Met Polypeptide Lys Phe Figure 10.8B “Central Dogma” = DNA to RNA to protein

  37. How RNA helps • 1. Ribosome attaches to mRNA • 2. Transfer RNA (tRNA) brings amino acids to ribosome

  38. Amino acid attachment site Anticodon Figure 10.11B, C Transfer RNA • One amino acid attached to one end • 3-base set on other end called “anticodon” • Anticodon is complement to a specific codon

  39. tRNAmolecules Growingpolypeptide Largesubunit mRNA Small subunit Figure 10.12A • 10.12 Ribosomes build polypeptides • Made of proteins and ribosomal RNA (rRNA)

  40. The ribosome • Holds tRNA and mRNA close together • Helps bond form between amino acids tRNA-binding sites Largesubunit Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNA-binding site mRNA Smallsubunit Codons Figure 10.12B, C

  41. 10.12 Ribosomes build polypeptides TRANSLATION: decode message to make protein

  42. Translation 1. Begins at “start” codon 2. Amino acids are set in sequence, according to the code on mRNA 3. Ends at “stop” codon

  43. Start of genetic message End Figure 10.13A • 10.13 A start (“initiation”) codon marks the start of an mRNA message

  44. Initiation codon = Start tRNA bring amino acids in sequence of code on mRNA Peptide bond forms between two amino acids tRNA released Elongation – polypeptide grows as amino acids join Termination codon = Stop

  45. Elongation

  46. DNA Transcription Polypeptide tRNA mRNA Translation

  47. 1 Codon recognition 2 Peptide bondformation Translocation 3 Aminoacid Polypeptide P site A site Anticodon mRNA Codons mRNAmovement Stopcodon New Peptidebond Figure 10.14

  48. 10.15 Review: The flow of genetic information in the cell is DNARNAprotein • Sequence of bases in DNA sequence of codons in mRNA  primary structure of a polypeptide DNA  mRNA  tRNA  amino acids  protein

  49. Genetic information: DNA to RNA to protein Sequence of codons  primary structure of protein

  50. Peptide bonds join amino acids into a polypeptide Polypeptide Transfer RNAs tRNA anticodons mRNA codons Sequence of amino acids determines 3-D shape of protein

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