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Genes and Protein Synthesis

Chapter 7. Genes and Protein Synthesis. DNA contains all of our hereditary information Genes are located in our DNA ~25,000 genes in our DNA (46 chromosomes) Each Gene codes for a specific polypeptide. One Gene-One Polypeptide Hypothesis. Central Dogma Francis Crick (1956). Main Idea.

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Genes and Protein Synthesis

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  1. Chapter 7 Genes and Protein Synthesis

  2. DNA contains all of our hereditary information Genes are located in our DNA ~25,000 genes in our DNA (46 chromosomes) Each Gene codes for a specific polypeptide One Gene-One Polypeptide Hypothesis

  3. Central Dogma • Francis Crick (1956) Main Idea

  4. Transcription • DNA to RNA • Translation • Assembly of amino acids into polypeptide • Using RNA Overall Process Gene 1 Gene 3 DNA molecule Gene 2 DNA strand TRANSCRIPTION RNA Codon TRANSLATION Polypeptide Amino acid

  5. RNA transcription • Initiation, Elongation, Termination • TATA box • Introns, Exons • mRNA, tRNA, rRNA • Translation • Ribosome • Codon • Amino Acids • Polypeptide Key Terms

  6. Protein is made of amino acid sequences 20 amino acids How does DNA code for amino acid? DNA to Protein

  7. Codon • Three letter code • 5’ to 3’ order • Start codon • Stop codon • AA are represented by more than one codon • 61 codons that specify AA Genetic COde

  8. Abbreviated • Three letters Amino acids

  9. DNA to RNA • Occurs in nucleus • Three process • Initiation • Elongation • Termination RNA polymerase Transcription DNA of gene Promoter DNA Terminator DNA Initiation Elongation Termination GrowingRNA Completed RNA RNApolymerase

  10. RNA polymerase binds to DNA • Binds at promoter region • TATA box • RNA polymerase unwinds DNA • Transcription unit • Part of gene that is transcribed initiation

  11. Transcription factors bind to specific regions of promoter Provide a substrate for RNA polymerase to bind beginning transcription Forms transcription initiation complex initiation

  12. RNA molecule is built • RNA polymerase • Primer not needed • 5’ to 3’ • 3’ to 5’ DNA is template strand • Coding strand • DNA strand that is not copied • Produces mRNA • Messenger RNA • DNA double helix reforms Elongation

  13. RNA polymerase recognizes a termination sequence – AAAAAAA Nuclear proteins bind to string of UUUUUU on RNA mRNA molecule releases from template strand Termination

  14. Pre-mRNA undergoes modifications before it leaves the nucleus • Poly(A) tail • Poly-A polymerase • Protects from RNA digesting enzymes in cytosol • 5’ cap • 7 G’s • Initial attachment site for mRNA’s to ribosomes • Removal of introns Post-transcriptional modifications

  15. DNA comprised of • Exons – sequence of DNA or RNA that codes for a gene • Introns – non-coding sequence of DNA or RNA • Spliceosome • Enzyme that removes introns from mRNA Splicing the pre-MRNa

  16. Spliceosome contains a handful of small ribonucleoproteins • snRNP’s (snurps) • snRNP’s bind to specific regions on introns Splicing Process

  17. Increases number and variety of proteins encoded by a single gene ~25,000 genes produce ~100,000 proteins Alternative Splicing

  18. mRNA to protein Ribosomes read codons tRNA assists ribosome to assemble amino acids into polypeptide chain Takes place in cytoplasm Translation

  19. Contains • triplet anticodon • amino acid attachment site • Are there 61 tRNA’s to read 61 codons? tRNA

  20. First two nucleotides of codon for a specific AA is always precise • Flexibility with third nucleotide • Aminoacylation – process of adding an AA to a tRNA • Forming aminoacyl-tRNA molecule • Catalyzed by 20 different aminoacyl-tRNAsynthetase enzymes TRNa: Wobble Hypothesis

  21. Translate mRNA chains into amino acids • Made up of two different sized parts • Ribosomal subunits (rRNA) • Ribosomes bring together mRNA with aminoacyl-tRNAs • Three sites • A site - aminoacyl • P site – peptidyl • E site - exit Ribosomes

  22. Amino acid • Three stages • Initiation • Elongation • Termination Polypeptide Translation process Asite P site Anticodon mRNA 1 Codon recognition mRNAmovement Stopcodon Newpeptidebond 2 Peptide bond formation 3 Translocation

  23. Ribosomal subunits associate with mRNA • Met-tRNA (methionine) • Forms complex with ribosomal subunits • Complex binds to 5’cap and scans for start codon (AUG) – known as scanning • Large ribosomal subunit binds to complete ribosome • Met-tRNA is in P-site Initiation • Reading frame is established to correctly readcodons

  24. Amino acids are added to grow a polypeptide chain A, P, and E sites operate 4 Steps Elongation

  25. A site arrives at a stop codon on mRNA • UAA, UAG, UGA • Protein release factor binds to A site releasing polypeptide chain • Ribosomal subunits, tRNA release and detach from mRNA Termination

  26. polysome b a What molecules are present in this photo? Red object = ?

  27. Throughout cell Single type of RNA polymerase transcribes all types of genes No introns mRNA ready to be translated into protein mRNA is translated by ribosomes in the cytosol as it is being transcribed ProkaryoticRNAtranscription/Translation

  28. What is a gene? Where is it located? What is the main function of a gene? Do we need our genes “on” all the time? How do we turn genes “on” or “off”? Review

  29. Proteins are not required by all cells at all times • Regulated • Eukaryotes – 4 ways • Transcriptional (as mRNA is being synthesized) • Post-transcriptional (as mRNA is being processed) • Translational (as proteins are made) • Post-translational (after protein has been made) • Prokaryotes • lacOperon • trpOperon Regulating Gene expression

  30. Most common • DNA wrapped around histones keep gene promoters inactive • Activator molecule is used (2 ways) • Signals a protein remodelling complex which loosen the histones exposing promoter • Signals an enzyme that adds an acetyl group to histones exposing promoter region Transcriptional regulation

  31. Methylation • Methyl groups are added to the cytosine bases in the promoter of a gene (transcription initiation complex) • Inhibits transcription – silencing • Genes are placed “on hold” until they are needed • E.g. hemoglobin Transcriptional regulation

  32. Agouti mice

  33. Pre-mRNA processing • Alternative splicing • Rate of mRNA degradation • Masking proteins – translation does not occur • Embryonic development • Hormones - directly or indirectly affect rate • Casein – milk protein in mammary gland • When casein is needed, prolactinis produced extending lifespan of casein mRNA Post transcriptional regulation

  34. Occurs during protein synthesis by a ribosome • Changes in length of poly(A) tail • Enzymes add or delete adenines • Increases or decreases time required to translate mRNA into protein • Environmental cues Translational regulation

  35. Processing • Removes sections of protein to make it active • Cell regulates this process (hormones) • Chemical modification • Chemical groups are added or deleted • Puts the protein “on hold” • Degradation • Proteins tagged with ubiquitin are degraded • Amino acids are recycled for protein synthesis Post-translational regulation

  36. lacOperon • Regulates the production of lactose metabolizing proteins Prokaryotic Regulation

  37. trpOperon • Regulates the expression of tryptophan enzymes Prokaryotic Regulation

  38. Lack regulatory mechanisms • Mutations in genetic code (mutagens) • Probability increases over lifetime • Radiation, smoking, chemicals • Mutations are passed on to daughter cells • Can lead to a mass of undifferentiated cells (tumor) • Benign and malignant • Oncogenes • Mutated genes that once served to stimulate cell growth • Cause undifferentiated cell division Cancer

  39. cancer

  40. Positive and negative • Natural selection – evolution • Cancer –death • Small-Scale – single base pair • Point mutations • Substitution, insertion/deletion, inversion • Large-Scale – multiple base pairs Genetic mutations

  41. Four groups • Missense, nonsense, silent, frameshift • Lactose, sickle cell anemia • SNPs – single nucleotide polymorphisms • Caused by point mutations Small-scale mutations

  42. Change of a single base pair or group of base pairs Results in the code for a different amino acid Protein will have different sequence and structure and may be non-functional or function differently Missense mutation

  43. Change in single base pair or group of base pairs Results in premature stop codon Protein will not be able to function Nonsense mutation

  44. Change in one or more base pairs Does not affect functioning of a gene Mutated DNA sequence codes for same amino acid Protein is not altered Silent mutation

  45. One or more nucleotides are inserted/deleted from a DNA sequence Reading frame of codons shifts resulting in multiple missense and/or nonsense effects Any deletion or insertion of base pairs in multiples of 3 does not cause frameshift Frameshift mutation

  46. Multiple nucleotides, entire genes, whole regions of chromosomes Large-scale mutations

  47. Amplification – gene duplication • Entire genes are copied to multiple regions of chromosomes Large-scale mutations

  48. Large-scale deletions • Entire coding regions of DNA are removed • Muscular Dystrophy Large-scale mutations

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