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Chapter 17

Chapter 17. From Gene to Protein. Basic Principles of Transcription and Translation. Transcription = DNA  mRNA ( mRNA = messenger RNA ) Translation = mRNA  polypeptide Occurs on ribosomes. Basic Principles of Transcription and Translation. Transcription = DNA  mRNA

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Chapter 17

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  1. Chapter 17 From Gene to Protein

  2. Basic Principles of Transcription and Translation • Transcription = DNA mRNA (mRNA =messenger RNA) • Translation = mRNApolypeptide • Occurs on ribosomes

  3. Basic Principles of Transcription and Translation • Transcription = DNA mRNA (mRNA =messenger RNA) • Translation = mRNApolypeptide • Occurs on ribosomes DNA mRNApolypeptide

  4. Prokaryotes • Transcription and translation occur together Figure 17.3a

  5. Eukaryotes- • Transcription occurs in nucleus

  6. Eukaryotes- • RNA transcripts are modified before becoming true mRNA

  7. Eukaryotes- • Translation occurs in cytoplasm

  8. Cellular chain of command • DNARNAamino acid (protein)

  9. Codons: Triplets of Bases

  10. Codons: Triplets of Bases Codon

  11. Codons: Triplets of Bases

  12. Cracking the Code • Codon = 1. Translated into an amino acid 2. Serves as a translational start/stop signal

  13. DNA sequences in gene: • CCTCAGAGTGTG • TACGTTGCGCCC TRANSCRIPTION • RNA sequence = ? TRANSLATION • Amino acid sequence = ?

  14. Codons must be read in the correct reading frame • Ex: “The red dog ate the cat” • Change reading frame “her edd oga tet hec at”

  15. Concept 17.2: Transcription • DNARNA: a closer look

  16. RNA synthesis Catalyzed by RNA polymerase 1. Pries the DNA strands apart 2. Adds and Hooks together the RNA nucleotides

  17. Synthesis of an RNA Transcript • 3 stages of transcription: 1. Initiation 2. Elongation 3. Termination

  18. 1. Initiation

  19. Initiation

  20. 2. Elongation

  21. 3. Termination

  22. Synthesis of an RNA Transcript

  23. Transcription Elongation

  24. 3 steps of transcription • 1. Initiation –more specific in Eukaryotes • 2. Elongation • 3. Termination

  25. Initiation of Transcription Prokaryote Vs. Eukaryote Promoters: Prok. = RNA Pol Bind to promoter sequence Euk. = Transcription factors bind first to TATA box then RNA pol II binds

  26. Concept 17.4 • Translation = RNA directed synthesis of a polypeptide • mRNApolypeptide

  27. Translation • Takes place in the cytoplasm • Ribosome attaches to an mRNA • Codon mRNA messagepolypeptide by tRNA

  28. Amino acid attachment site tRNA- transfer RNA: 1. specific amino acid attachment site 2. base triplet called an anticodon on one end ANTI-CODON

  29. Amino acid? tRNA- transfer RNA: 1. specific amino acid attachment site 2. base triplet called an anticodon on one end Anti-Codon? GGA

  30. Glycine tRNA- transfer RNA: 1. specific amino acid attachment site 2. base triplet called an anticodon on one end CCU GGA

  31. Ribosomes have 2 subunits (small + large) • Hold the tRNA and mRNA close together during translation tRNA binding sites Large Subunit P A E P A mRNA binding site Small Subunit

  32. Building a Polypeptide • We can divide translation into three stages • Initiation • Elongation • Termination

  33. Initiation mRNA, tRNA, and ribosome subunits assemble

  34. Elongation: step 1- codon recognition 2 2 1 1

  35. Elongation: Step 2- peptide bond formation 2 1 2 1 1 2

  36. Elongation: 2 1 1 2

  37. Elongation: Step 3- translocation 3 2 2 1 1 2 1 2

  38. Termination of Translation: Step 3 • Ribosome reaches a stop codon in the mRNA Release Factor

  39. Concept 17.7 • Mutations- changes in the genetic material of a cell • Point mutations • changes in just one base pair of a gene

  40. Normal Figure 17.23

  41. Normal Point Mutation Figure 17.23

  42. Types of Point Mutations • Point mutations • Base-pair substitutions • Base-pair insertions or deletions

  43. Substitutions • A base-pair substitution • Can cause missense or nonsense Figure 17.24

  44. Missense

  45. Nonsense

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