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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. 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

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

  13. 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

  14. 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

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

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

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

  18. Contains • triplet anticodon • amino acid attachment site • Are there 61 tRNA’sto read 61 codons? tRNA

  19. 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

  20. 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

  21. 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

  22. 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

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

  24. 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

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

  26. 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

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