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Chapter 17

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This chapter elucidates the fundamental processes of transcription and translation, which are pivotal for gene expression. Transcription converts DNA into mRNA in the nucleus (in eukaryotes), while translation occurs in the cytoplasm, synthesizing polypeptides from mRNA sequences. Key concepts include the roles of RNA polymerase, codons, tRNA, and ribosomal activity. Differences between prokaryotic and eukaryotic processes are highlighted, along with the stages of both transcription (initiation, elongation, termination) and translation. The significance of mutations and their potential impacts on protein synthesis are also discussed.

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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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