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CHAPTER 10 Protein Synthesis

CHAPTER 10 Protein Synthesis. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN. The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits. The information constituting an organism’s genotype is carried in the sequence of bases in DNA

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CHAPTER 10 Protein Synthesis

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  1. CHAPTER 10Protein Synthesis

  2. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits • The information constituting an organism’s genotype is carried in the sequence of bases in DNA • The flow of information is from DNA to RNA to protein

  3. The DNA is transcribed into RNA, which is translated into the polypeptide • A specific gene specifies a polypeptide http://www.wiley.com/legacy/college/boyer/0470003790/animations/central_dogma/central_dogma.swf DNA TRANSCRIPTION RNA TRANSLATION Protein Figure 10.6A

  4. Studies of the bread mold Neurospora crassa led to the one gene-one polypeptide hypothesis • Studies of inherited metabolic disorders first suggested that phenotype is expressed through proteins Figure 10.6B

  5. Mutate wild type fungus *Supply all mutant isolates with complete media *Grow purified mutants with minimal media to find nutritional mutants *Determine what is the nutritional limitation  find mutation

  6. There for the gene used to produce an enzyme that helps cells manufacture Arginine amino acid was mutated in that fungal strain

  7. Transcription produces genetic messages in the form of RNA RNA nucleotide RNApolymerase Direction oftranscription Templatestrand of DNA Newly made RNA Figure 10.9A

  8. RNA Transcription • Process in which the genetic information on DNA is transferred to RNA • During transcription only 1 DNA stand serves as the template or pattern from which RNA is formed.

  9. RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation • RNA nucleotides line up along one strand of the DNA following the base-pairing rules • The single-stranded messenger RNA peels away and the DNA strands rejoin • In transcription, the DNA helix unzips Elongation Area shownin Figure 10.9A Termination GrowingRNA Completed RNA RNApolymerase http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf Figure 10.9B

  10. RNA Transcription • Initiation • The enzyme RNA polymerase attaches to the promoter site on the DNA • Promoter – a sequence of nucleotides that is found on one of the DNA strands • tells RNA polymerase to start transcription and which of the two DNA strands to transcribe

  11. RNA Transcription • Elongation • RNA nucleotides attach to the free DNA nucleotides by hydrogen bonds one at a time • As RNA synthesis continues the growing RNA strand peels away from the DNA and the DNA strands rejoin

  12. RNA Transcription • Termination • RNA polymerase reaches the terminator. • Terminator – a sequence of bases on DNA that signals the end of the gene • The RNA polymerase detaches from the DNA and the RNA molecule is complete

  13. http://www.four-h.purdue.edu/apple_genomics/flash/movie3.swf 10.10 Eukaryotic RNA is processed before leaving the nucleus http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter14/animation_quiz_3.html Exon Intron Exon Intron Exon DNA TranscriptionAddition of cap and tail • Noncoding segments called introns are spliced out • The coding segments called exons are joined together • A cap and a tail are added to the ends Cap RNAtranscriptwith capand tail Introns removed Tail Exons spliced together mRNA Coding sequence NUCLEUS CYTOPLASM Figure 10.10

  14. Genetic information written in codons is translated into amino acid sequences • The “words” of the DNA “language” are triplets of bases called codons • The codons in a gene specify the amino acid sequence of a polypeptide

  15. Gene 1 Gene 3 DNA molecule Gene 2 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Amino acid Figure 10.7

  16. The genetic code is the Rosetta stone of life • Virtually all organisms share the same genetic code Figure 10.8A

  17. Transcribed strand • An exercise in translating the genetic code DNA Transcription RNA Startcodon Stopcodon Translation Polypeptide Figure 10.8B

  18. Translation • The process in which a polypeptide is synthesized using the genetic information encoded on an mRNA molecule • The following are needed for translation to occur • mRNA • Contains the instructions for the assembly of proteins • Codon – a sequence of 3 bases on mRNA that specifies a specific amino acid that will be added to the polypeptide chain

  19. Transfer RNA molecules serve as interpreters during translation Amino acid attachment site • In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide • The process is aided by transfer RNAs Hydrogen bond RNA polynucleotide chain Anticodon Figure 10.11A

  20. Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other Amino acidattachment site Anticodon Figure 10.11B, C

  21. Translation • tRNA (transfer RNA) • Carries an amino acid to the ribosome • A tRNA molecule is composed of • A single strand of RNA (about 80 nucleotides) • A loop at one end that contains the anticodon • Anticodon – a sequence of 3 bases on tRNA that are complementary to the bases on mRNA • At the opposite end of the loop is a site where an amino acit can attach

  22. Translation 3. Amino acids • Located in the cytoplasm • Synthesized from other chemicals or obtained from food

  23. 10.12 Ribosomes build polypeptides Next amino acidto be added topolypeptide Growingpolypeptide tRNA molecules P site A site Growingpolypeptide Largesubunit tRNA P A mRNA mRNAbindingsite Codons mRNA Smallsubunit Figure 10.12A-C

  24. Translation • Ribosomes • Organelles where protein synthesis occurs • Consists of 2 subunits each made up of proteins and ribosomal RNA (rRNA) • Small subunit – has binding site for mRNA • Large subunit – has binding site for tRNA

  25. An initiation codon marks the start of an mRNA message Start of genetic message End Figure 10.13A

  26. mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Largeribosomalsubunit Initiator tRNA P site A site Startcodon Small ribosomalsubunit mRNA 1 2 Figure 10.13B

  27. Newpeptidebondforming Growing polypeptide Stage Elongation 4 A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. Codons mRNA Polypeptide Stage Termination 5 The ribosome recognizes a stop codon. The poly-peptide is terminated and released. Stop Codon Figure 10.15 (continued)

  28. 10.14 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation • The mRNA moves a codon at a time relative to the ribosome • A tRNA pairs with each codon, adding an amino acid to the growing polypeptide

  29. Amino acid Polypeptide Asite P site Anticodon mRNA 1 Codon recognition mRNAmovement Stopcodon Newpeptidebond 2 Peptide bond formation 3 Translocation Figure 10.14

  30. Steps of Translation • Initiation • mRNA binds to the ribosome • The start codon (AUG) is reached • The first amino acid (methionine) is brought to the ribosome by the tRNA • Elongation • Amino acids are added one by one to a growing polypeptide chain

  31. Steps of Translation • Termination • The stop codon is reached • The completed polypeptide is released

  32. Modification of the polypeptide Endoplasmic reticulum • Collects proteins made by the ribosomes • Packages them into vesicles which move to the Golgi apparatus Golgi apparatus • Proteins are altered, packaged into vesicles, and transported to different parts of the cell or exported out of the cell

  33. TRANSCRIPTION DNA Stage mRNA istranscribed from aDNA template. 1 mRNA RNApolymerase • Summary of transcription and translation Amino acid TRANSLATION Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 2 Enzyme tRNA Initiator tRNA Anticodon Stage Initiation of polypeptide synthesis 3 Largeribosomalsubunit The mRNA, the first tRNA, and the ribosomal subunits come together. Start Codon Smallribosomalsubunit mRNA Figure 10.15

  34. Review: The flow of genetic information in the cell is DNARNAprotein • The sequence of codons in DNA spells out the primary structure of a polypeptide • Polypeptides form proteins that cells and organisms use

  35. Mutations can change the meaning of genes • Mutations are changes in the DNA base sequence • These are caused by errors in DNA replication or by mutagens • The change of a single DNA nucleotide causes sickle-cell disease

  36. Normal hemoglobin DNA Mutant hemoglobin DNA mRNA mRNA Normal hemoglobin Sickle-cell hemoglobin Glu Val http://www.cleanvideosearch.com/media/action/yt/watch?v=1fN7rOwDyMQ&safety_mode=true&persist_safety_mode=1&safe=active Figure 10.16A

  37. NORMAL GENE • Types of mutations mRNA Protein Met Lys Phe Gly Ala BASE SUBSTITUTION Met Lys Phe Ser Ala Missing BASE DELETION Met Lys Leu Ala His Figure 10.16B

  38. Types of Mutations There are 2 general categories of mutations: • Base substitution • The replacement of one nucleotide with another • Can result in no change in the protein • An insignificant change • The altered amino acid has no effect on the function of the protein

  39. Types of Mutations • A change that is crucial to life of the organism • The altered amino acid has an effect on the function of the protein • Base insertions or deletions • One or more bases are added or deleted from the DNA • Often have disastrous effects • The nucleotide sequence following the change alters the genetic message (reading frame)

  40. Mutations are Useful Mutations are useful because they • Provide diversity that allows evolution by natural selection to occur • Essential tool for geneticists • Create different alleles needed for genetic research

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