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Protein Synthesis

Protein Synthesis. Chapter 17. Protein synthesis. DNA Responsible for hereditary information DNA divided into genes Gene: Sequence of nucleotides Determines amino acid sequence in proteins Genes provide information to make proteins. Protein synthesis.

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Protein Synthesis

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  1. Protein Synthesis Chapter 17

  2. Protein synthesis • DNA • Responsible for hereditary information • DNA divided into genes • Gene: • Sequence of nucleotides • Determines amino acid sequence in proteins • Genes provide information to make proteins

  3. Protein synthesis DNA RNA protein

  4. Central Dogma • Mechanism of reading & expressing genes • Information passes from the genes (DNA) to an RNA copy • Directs sequence of amino acids to make proteins

  5. Protein synthesis • Transcription: • DNA sequence is copied into an RNA • Translation: • Information from the RNA is turned into an amino acid sequence

  6. RNA • RNA (ribonucleic acid) • Single strand • Sugar –ribose (-OH on 2’ carbon) • Uracil instead of thymine

  7. RNA • mRNA: • Messenger RNA • Transcribes information from DNA • Codons • (3 nucleotides) CGU • mRNA • Codes for amino acids • rRNA: • Ribosomal RNA • Polypeptides are assembled

  8. RNA • tRNA: • Transfer RNA • Transports aa to build proteins • Positions aa on rRNA • Anticodons • (3 complementary nucleotides) GCA

  9. Cracking the code • Francis Crick • Codons (Triplet code)-mRNA • Each codon corresponds to an aa • 20 amino acids • Reading frame • Reading symbols in correct groupings

  10. Cracking the code • 1 or 2 deletions or additions • Gene was transcribed incorrectly • 3 deletions • Reading frame would shift • Gene was transcribed correctly

  11. WHYDIDTHEREDCATEATTHEFATRAT WHYIDTHEREDCATEATTHEFATRAT WHYDTHEREDCATEATTHEFATRAT WHYTHEREDCATEATTHEFATRAT

  12. The code • Universal code • AGA codes for amino acid Arginine • Humans & bacteria • Genes from humans can be transcribed by mRNA from bacteria • Produce human proteins • Insulin

  13. Protein synthesis DNA RNA Protein Transcription Translation

  14. Prokaryotes • Transcription • Getting the code from DNA • Template strand • Strand of DNA that is transcribed or read • Transcribed RNA is complementary to the DNA

  15. Prokaryotes • Coding strand • DNA strand not coded • Same sequence of nucleotides as the RNA transcript • Only T instead of U.

  16. Prokaryotes • RNA polymerase • Enzyme • Adds nucleotides to the 3’end • 5’to3’ direction • Does not need a primer to start

  17. Prokaryotes • Stages of transcription • Initiation • Elongation • Termination

  18. Prokaryotes • Initiation • Promoters: • Sequence on DNA where transcription starts • -35 sequence TTGACA • -10 sequence TATAAT • Sequences are not transcribed

  19. Prokaryotes • RNA polymerase binds promoter • Unwinds DNA • Uses an ATP or GTP to start • Uses phosphate group • Transcription bubble: • RNA polymerase, DNA & growing RNA strand

  20. Prokaryotes • Termination • Stop signal • Sequence on DNA • RNA transcript signals polymerase to detach from DNA • RNA strand separates from the DNA

  21. Prokaryotes • Translation • Passing the code to make a polypeptide • mRNA binds to rRNA on the ribosome • mRNA attaches so only one codon is exposed at a time

  22. Ribosome • Located in the cytoplasm • Site of translation • 2 subunits composed of protein & RNA • Small (20 proteins and 1 RNA) • Large (30 proteins and 2 RNA) • 3 sites on ribosome surface involved in protein synthesis • E, P, and A sites

  23. Ribosome

  24. Ribosome

  25. Prokaryotes • tRNA (anti-codon) • Complementary sequence • Binds to mRNA • tRNA carries a specific amino acid • Adds to growing polypeptide • 45 tRNA’s

  26. Prokaryotes • Aminoacyl-t-RNA synthetases • Activating enzymes • Link correct tRNA code to correct aa • One for each 20 amino acids • Some read one code, some read several codes

  27. Prokaryotes • Nonsense codes • UAA, UAG, UGA code to stop • AUG codes for start as well as methionine • Ribosome starts at the first AUG it comes across in the code

  28. Prokaryotes • Translation • 1. Initiation • 2. Elongation • 3. Termination

  29. Prokaryotes • Initiation • Initiation complex • 1. tRNA with formylmethionine attached binds to a small ribosome • 2. Initiation factors position the tRNA on the P site • 3. A site (aminoacyl) where other tRNA’s form

  30. Prokaryotes • 4. tRNA is positioned on to the mRNA at AUG • 5. Attachment of large ribosomal unit

  31. Prokaryotes • Elongation factors • Help second tRNA bind to the A-site • Two amino acids bind (peptide bond) • Translocation: • Ribosome moves 3 more nucleotides along mRNA in the 5’to 3’ direction

  32. Prokaryotes • Initial tRNA moves to E site • Released • New tRNA moves into A site • Continues to add more aa to form the polypeptide

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