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Chapter 14

Chapter 14. From DNA to Protein. Marvelous Mussel Adhesive. Mussel binds itself to rocks with threads coated with the protein bysuss Gene for bysuss has been put into yeast Yeast synthesize the protein based on the instructions in the mussel DNA. Steps from DNA to Proteins.

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Chapter 14

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  1. Chapter 14 From DNA to Protein

  2. Marvelous Mussel Adhesive • Mussel binds itself to rocks with threads coated with the protein bysuss • Gene for bysuss has been put into yeast • Yeast synthesize the protein based on the instructions in the mussel DNA

  3. Steps from DNA to Proteins Same two steps produce all proteins: 1) DNA is transcribed to form RNA • Occurs in the nucleus • RNA moves into cytoplasm 2) RNA is translated to form polypeptide chains, which fold to form proteins

  4. Bozeman video—dna/rna part 2 http://www.youtube.com/watch?v=W4mYwsr9gGE

  5. Three Classes of RNAs • Messenger RNA • Carries protein-building instruction • Ribosomal RNA • Major component of ribosomes • Transfer RNA • Delivers amino acids to ribosomes

  6. A Nucleotide Subunit of RNA uracil (base) phosphate group sugar (ribose) Fig. 14-2, p. 220

  7. Base Pairing during Transcription DNA base pairing during transcription RNA DNA base pairing during DNA replication DNA Fig. 14-2c, p.220

  8. Transcription & DNA Replication • Like DNA replication • Nucleotides added in 5’ to 3’ direction • Unlike DNA replication • Only small stretch is template • RNA polymerase catalyzes nucleotide addition • Product is a single strand of RNA

  9. Promoter • A base sequence in the DNA that signals the start of a gene • For transcription to occur, RNA polymerase must first bind to a promoter

  10. Promoter promoter region RNA polymerase, the enzyme that catalyzes transcription a RNA polymerase initiates transcription at a promoter region in DNA. It recognizes a base sequence located next to the promoter as a template. It will link the nucleotides adenine, cytosine, guanine, and uracil into a strand of RNA, in the order specified by DNA. Fig. 14-3a, p.220

  11. Gene Transcription DNA template at selected transcription site newly forming RNA transcript DNA template winding up DNA template unwinding b All through transcription, the DNA double helix becomes unwound in front of the RNA polymerase. Short lengths of the newly forming RNA strand briefly wind up with its DNA template strand. New stretches of RNA unwind from the template (and the two DNA strands wind up again). Fig. 14-3b, p.220

  12. Adding Nucleotides direction of transcription 3´ 5´ 5´ 3´ growing RNA transcript c What happened at the assembly site? RNA polymerase catalyzed the assembly of ribonucleotides, one after another, into an RNA strand, using exposed bases on the DNA as a template. Many other proteins assist this process. Fig. 14-3c, p.221

  13. Transcript Modification unit of transcription in a DNA strand exon intron exon intron exon transcription into pre-mRNA poly-A tail cap snipped out snipped out mature mRNA transcript Fig. 14-4, p.221

  14. transcription into pre-mRNA poly-A tail cap 5’ 3’ snipped out snipped out 5’ 3’ mature mRNA transcript unit of transcription in a DNA strand exon intron exon intron exon 5’ 3’ Stepped Art Fig. 14-4, p.221

  15. Genetic Code • Set of 64 base triplets • Codons • 61 specify amino acids • 3 stop translation Fig. 14-6, p.222

  16. Genetic Code DNA mRNA mRNA codons amino acids threonine proline glutamate glutamate lysine Fig. 14-5, p.222

  17. tRNA Structure codon in mRNA anticodon amino-acid attachment site amino acid OH Figure 14.7Page 223

  18. tRNA Structure codon in mRNA anticodon in tRNA amino acid Fig. 14-7, p.223

  19. TRANSCRIPTION TO TRANSLATION

  20. Ribosomes funnel large ribosomal subunit intact ribosome + small ribosomal subunit Fig. 14-8, p.223

  21. Three Stages of Translation Initiation Elongation Termination

  22. Initiation • Initiator tRNA binds to small ribosomal subunit • Small subunit/tRNA complex attaches to mRNA and moves along it to an AUG “start” codon • Large ribosomal subunit joins complex

  23. Binding Sites binding site for mRNA A (second binding site for tRNA) P (first binding site for tRNA)

  24. Elongation • mRNA passes through ribosomal subunits • tRNAs deliver amino acids to the ribosomal binding site in the order specified by the mRNA • Peptide bonds form between the amino acids and the polypeptide chain grows

  25. Elongation

  26. Termination • Stop codon into place • No tRNA with anticodon • Release factors bind to the ribosome • mRNA and polypeptide are released mRNA new polypeptide chain

  27. What Happens to the New Polypeptides? • Some just enter the cytoplasm • Many enter the endoplasmic reticulum and move through the cytomembrane system where they are modified

  28. Transcription Overview rRNA tRNA mRNA Mature mRNA transcripts ribosomal subunits mature tRNA Translation

  29. elongation binding site for mRNA P (first binding site for tRNA) A (second binding site for tRNA) Amino Acid 1 Amino Acid 1 Amino Acid 2 c Initiation ends when a large and small ribosomal subunit converge and bind together. Amino Acid 2 d The initiator tRNA binds to the ribosome. e One of the rRNA molecules b Initiation, the first stage of translating mRNA, will start when an initiator tRNA binds to a small ribosomal subunit. initiation a A mature mRNA transcript leaves the nucleus through a pore in the nuclear envelope. Fig. 14-9a-e, p.224

  30. g A third tRNA binds with the next codon f The first tRNA is released h Steps f and g are repeated termination i A STOP codon moves into the area where the chain is being built. j The new polypeptide chain is released from the ribosome. k The two ribosomal subunits now separate, also. Fig. 14-9f-k, p.224

  31. Bozeman video—transcription & translation http://www.youtube.com/watch?v=h3b9ArupXZg

  32. Bozeman & other--Central dogma videos http://www.youtube.com/watch?v=yLQe138HY3s http://www.youtube.com/watch?v=DISBuAsg0uE

  33. Gene Mutations Base-Pair Substitutions Insertions Deletions

  34. Bozeman Video--mutations http://www.youtube.com/watch?v=eDbK0cxKKsk

  35. Base-Pair Substitution a base substitution within the triplet (red) original base triplet in a DNA strand During replication, proofreading enzymes make a substitution possible outcomes: or original, unmutated sequence a gene mutation

  36. Frameshift Mutations • Insertion • Extra base added into gene region • Deletion • Base removed from gene region • Both shift the reading frame • Result in many wrong amino acids

  37. Frameshift Mutation part of DNA template mRNA transcribed from DNA resulting amino acid sequence THREONINE PROLINE GLUTAMATE GLUTAMATE LYSINE base substitution in DNA altered mRNA altered amino acid sequence THREONINE PROLINE VALINE GLUTAMATE LYSINE deletion in DNA altered mRNA THREONINE PROLINE GLYCINE ARGININE altered amino acid sequence Fig. 14-10, p.226

  38. Transposons • DNA segments that move spontaneously about the genome • When they insert into a gene region, they usually inactivate that gene

  39. Transposons • Barbara McClintock • Nonuniform coloration of kernels in strains of indian corn Fig. 14-11, p.227

  40. Mutation Rates • Each gene has a characteristic mutation rate • Average rate for eukaryotes is between 10-4 and 10-6 per gene per generation • Only mutations that arise in germ cells can be passed on to next generation

  41. Mutagens • Ionizing radiation (X rays) • Nonionizing radiation (UV) • Natural and synthetic chemicals

  42. Fig. 14-14, p.229

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