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DNA

DNA. C. G. T. A. Hydrogen bond. T. A. Base pair. T. A. G. C. G. C. G. C. A. T. C. G. C. G. T. A. A. T. A. T. T. A. T. A. G. C. A. T. Computer model. Ribbon model. Partial chemical structure. Animation: Campbell Ch 10 – DNA Double Helix.

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DNA

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  1. DNA C G T A Hydrogen bond T A Base pair T A G C G C G C A T C G C G T A A T A T T A T A G C A T Computer model Ribbon model Partial chemical structure Animation: Campbell Ch 10 – DNA Double Helix

  2. What does the cell use DNA for? • Gives you traits But how?

  3. What IS a trait? • Physical structure produced by a protein! • DNA controls the production of proteins. DNA  Proteins

  4. What do we know about making proteins? DNA is in the NUCLEUS RIBOSOMES, ER, and GOLGI are in the CYTOPLASM

  5. How does that work? • RNA acts as a messenger to carry information from the DNA in the nucleus to the ribosomes in the cytoplasm DNA  RNA  Proteins

  6. Nitrogenous base (A, G, C, or U) What’s RNA? Phosphate group • Nucleic Acid • Similar to DNA • Some differences Uracil (U) Sugar (ribose)

  7. What’s RNA? Animation: Campbell Ch 10 – 10_2 DNA and RNA Structure

  8. Protein Synthesis Overview DNA is located in the NUCLEUS

  9. Protein Synthesis Overview A messenger RNA (mRNA) copy is made of DNA.

  10. Protein Synthesis Overview mRNA leaves the nucleus and goes to the ribosome

  11. Protein Synthesis Overview Ribosome uses mRNA to assemble amino acids in the correct order to make a specific protein

  12. Genes to Polypeptides • Polypeptides = chains of AA = proteins • 20 different AA exist • specific polypeptide has specific AA sequence • Sequence of AA determines the shape and function of a protein

  13. Genes to Polypeptides • Sequence of bases in DNA determine AA sequence • “Genes” store order of AA in a code in DNA • One specific gene will yield one* specific polypeptide • polypeptide = protein that does a job!

  14. DNA & Genetic Code • There are 20 amino acids, and a stop • How can DNA specify 21 things with only four bases?

  15. Genetic Code • IF: 1 base = 1 amino acid • THEN: how many amino acid possibilities are there? G A T C 4

  16. Genetic Code • IF: 2 bases = 1 amino acid • THEN: how many amino acid possibilities are there? G A T C G A T C 4 x 4 = 16

  17. Genetic Code • IF: 3 bases = 1 amino acid • THEN: how many amino acid possibilities are there? G A T C G A T C G A T C 4 x 4 x 4 = 64

  18. DNA & Genetic Code • In a gene, every three bases code for a specific amino acid (one of the 20) • 4 x 4 x 4 = 64 total possiblities • One amino acid can be coded for by more than one triplet

  19. DNA & Genetic Code Genetic code is composed of codons made up of of base triplets

  20. DNA & Genetic Code • The genetic code is both universal and degenerate. • Universal = found in all living organisms • Degenerate = having more than one base triplet (codon) to code for one amino acid

  21. Protein Synthesis Overview • DNA is located in the nucleus DNA

  22. Protein Synthesis Overview • Ribosomes are located in the cytoplasm DNA

  23. Protein Synthesis Overview • Messenger RNA carries “message” from DNA to ribosomes DNA

  24. Transcription • Genes are made of DNA • DNA cannot leave the nucleus • A copy must be “transcribed” into RNA • RNA exits nucleus http://www.fed.cuhk.edu.hk/~johnson/teaching/genetics/animations/transcription.htm

  25. Transcription • INITIATION: RNA polymerase uncoils DNA double helix • ELONGATION: RNA polymerase creates a new mRNA strand using free RNA nucleotides; a single DNA template strand is used

  26. Transcription • RNA nucleotides attached together (type of reaction?) via RNA polymerase • TERMINATION: New mRNA strands separates from DNA • DNA reforms Animation: Campbell Ch 10 – 10_9 Transcription

  27. What’s it look like? So, the new mRNA strand was just made, now what?

  28. Final Steps – Eukaryotes ONLY • mRNA Splicing • INTRONS: non-coding regions of the mRNA strand • EXONS: coding regions of the mRNA strand • Introns are spliced out of final mRNA

  29. Final Steps – Eukaryotes ONLY • 5’ Cap • Modification to 5’ end of mRNA • Ensures stability of mRNA

  30. Final Steps – Eukaryotes ONLY • 3’ poly-A tail • Addition of poly-A to 3’ end of mRNA • Protects RNA from nucleases

  31. Intron Exon Exon Exon Intron DNA Transcription Addition of cap and tail Cap RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Animation: Cain Ch13a03 - Transcription Cytoplasm

  32. Transcription in a cell • Multiple genes can be transcribed at the same time • The same gene can be transcribed at the same time

  33. Translation Nucleus Ribosome (cytoplasm) DNA mRNA Protein Transcription Translation Where we are now.

  34. Translation Summary • Instructions in the mRNA are used by a ribosome to assemble amino acids in the correct order • Order of amino acids gives the protein its shape • Shape gives protein its function

  35. Translation Summary The Key Players The Stages of Translation Initiation Elongation termination • mRNA • tRNA • rRNA Animation: Cain Ch13a07 - Translation

  36. mRNA (messenger RNA) • copy of the directions to make the product (protein) • tells the ribosome the correct sequence of Amino Acids while putting together the protein • each codon (3 bases) directs a specific amino acid to be added to the growing protein

  37. tRNA (transfer RNA) • the delivery RNA; delivers specific Amino Acids to the ribosome • composed of RNA • anticodon binds to a corresponding codon on mRNA • Carries one specific amino

  38. 6.4.1 Translation

  39. rRNA (ribosomal RNA) • ribosomes are made of RNA and protein • composed of two subunits: the 30s and 50s subunits • two tRNA binding sites; one mRNA binding site

  40. Translation INITIATION • small (30S) ribosome subunit binds to mRNA at the 5’ end of the mRNA • 30S moves along mRNA 5’ to 3’ until it hits the start codon AUG

  41. Translation INITIATION • large subunit binds • Methionine tRNA moves into ribosome

  42. Translation INITIATION • another tRNA, with the anticodon complementary to the next codon binds to the ribosome

  43. Translation ELONGATION • first amino acid added • ribosome moves down mRNA to next codon • next tRNA comes in • its amino acid is bound to the polypeptide chain • ribosome moves down mRNA to next codon

  44. Translation TERMINATION • the ribosome encounters a stop codon • no tRNA molecule has an anticodon for this codon

  45. Translation TERMINATION • polypeptide is released and ribosome disassociates Animation: Campbell Ch 10 – 10_14 Translation

  46. Where does translation happen? • Cytoplasmic (free) Ribosomes  proteins for use in cytoplasm • Rough ER (attached) Ribosomes  proteins secreted or used in lysosomes

  47. DNA molecule Gene 1 • DNA • TRANSCRIPTION • RNA • TRANSLATION • PROTEIN Gene 2 Gene 3 DNA strand C C G G C A A A A A A A Transcription C G G U U U U U C G U U RNA Codon Translation Polypeptide Amino acid

  48. Strand to be transcribed Interpreting the Genetic Code Second base C A U G UAU U UCU UUU UGU T T T T C C A A C A A A Cys Phe Tyr C UAC UGC UCC UUC DNA Ser U UUA UCA Stop A A UAA Stop UGA A A A A G T T T G G T T Leu G UGG Trp UCG UUG Stop UAG U CAU CCU CUU CGU His Transcription CUC C CCC CGU CAC Leu Pro Arg C A CUA CCA CAA CGA Gln G CUG CGG CCG CAG First base Third base U AUU ACU AAU AGU Ser Asn A A A A G G U U U U G U AUC lle C ACC AAC AGC RNA Thr A A AUA ACA AGA AAA Arg Lys Met or start G AUG AAG ACG AGG Stop codon Start codon U GUU GCU GAU GGU Translation Asp C GUC GCC GAC GGC G Val Gly Ala A GCA GUA GAA GGA Glu Animation: Starr Ch 14 – Genetic code GUG GCG G GAG GGG GAG Polypeptide Met Phe Lys

  49. Changes in the Genetic Code Normal hemoglobin DNA Mutant hemoglobin DNA • MUTATION = change in the nucleotide sequence of DNA T C T C A T mRNA mRNA A A G G U A Normal hemoglobin Sickle-cell hemoglobin Glu Val

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