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Protein Synthesis-Translation

Protein Synthesis-Translation. Warm-up #6. How is RNA different than DNA? Name the 3 steps of transcription. What is the end product of transcription? What is the difference between the sense and antisense DNA strands? What is the role of RNA polymerase?

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Protein Synthesis-Translation

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  1. Protein Synthesis-Translation

  2. Warm-up #6 • How is RNA different than DNA? • Name the 3 steps of transcription. • What is the end product of transcription? • What is the difference between the sense and antisense DNA strands? • What is the role of RNA polymerase? • Describe the initiation step in transcription. • What are the “extra” things that happens to the mRNA in eukaryotic cells BEFORE it leaves the nucleus?

  3. From nucleus to cytoplasm transcription protein DNA mRNA translation trait nucleus cytoplasm

  4. Things you will need to know in order to understand translation: 1. mRNA codon chart 2. Redundancy of the code 3. Structure of tRNA 4. Ribosome structure

  5. Redundant but not Ambiguous • Codons GAA and GAG both specify glutamic acid (redundancy) • Neither of them specifies any other amino acid (no ambiguity)

  6. mRNA Codons: ·  codon = group of 3 mRNA nucleotides **1 codon codes for 1 amino acid ·  During translation, proteins are synthesized according to the genetic message of sequential codons along the mRNA

  7. For ALL life! strongest support for a common origin for all life Code has duplicates several codons for each amino acid mutation insurance! The mRNA code • Start codon • AUG • methionine • Stop codons • UGA, UAA, UAG

  8. shows the “dictionary” for the mRNA codons and their corresponding amino acids (know how to use) 1. DNA: AGC-GTG-CCA 2. mRNA: 3. amino acid chain (protein): ______________________

  9. shows the “dictionary” for the mRNA codons and their corresponding amino acids (know how to use) 1. DNA: AGC-GTG-CCA 2. mRNA: UCG-CAC-GGU 3. amino acid chain (protein) = Serine- Histadine- Glycine

  10. tRNA Structure ·  Transfer RNA (tRNA) is the interpreter between the 2 forms of information: base sequence in mRNA and amino acid sequence in polypeptides

  11. -an enzyme links a specific amino acid from the cytosol/cytoplasm to each tRNA molecule on the 3’ end (CCA) using ATP for energy Amino acid location (CCA) 3 exposed bases

  12. Amino acid attachment site 5¢ 3¢ Hydrogen bonds LE 17-14b 3¢ 5¢ Anticodon Anticodon Three-dimensional structure Symbol that is widely used

  13. Amino acid Aminoacyl-tRNA synthetase (enzyme) LE 17-15 Pyrophosphate Phosphates tRNA AMP Aminoacyl tRNA (an “activated amino acid”)

  14. Amino acid ·  Molecules of tRNA are specific for only 1 amino acid -one end of tRNA attaches to a specific amino acid -the other end Hydrogen bonds to mRNA codon by base pairing (anticodon= a sequence of 3 bases on tRNA) tRNA anticodon mRNA codon

  15. Ribosome Structure • large ribosomal subunit (50s) • small ribosomal subunit (30s) • each subunit = ribosome/protein complex • Consists of an mRNA binding site plus 3 tRNA binding sites P E A

  16. P site (Peptidyl-tRNA binding site) LE 17-16b A site (Aminoacyl- tRNA binding site) E site (Exit site) E P A Large subunit mRNA binding site Small subunit Schematic model showing binding sites

  17. Process of Translation • Translation includes 4 processes: initiation, elongation, translocation, and termination

  18. 1. Initiation of Translation • mRNA binds to small ribosomal subunit • Initiator tRNA brings1st amino acid, Methionine (Met) to the initiation site on mRNA (start codon AUG= And UGo) • the Large ribosomal subunit binds • Met is in the “P” site • “A” site is available for the next tRNA

  19. Large ribosomal subunit LE 17-17 P site Met Met Initiator tRNA GTP GDP A E mRNA 5¢ 5¢ 3¢ 3¢ Start codon (AUG) Small ribosomal subunit mRNA binding site Translation initiation complex

  20. 2. Elongation • The next tRNA anticodon complementary base pairs with the mRNA codon in the “A” site aligning the appropriate amino acid next to “Met.” • Ribosome forms a peptide bond between “Met” and the 2nd amino acid and it passes the elongating polypetide chain to the tRNA in the “A” site

  21. 3. Translocation • Ribosome moves (translocates-change location) the tRNA in the “A” site to the “P” site • The empty tRNA moves to the “E” site where it is released • mRNA moves along/through the ribosome to expose the next mRNA codon to the “A” site • the protein chain is growing longer

  22. Fueled by GTP= Guanosine Triphosphate Amino end of polypeptide E 3¢ mRNA P site A site Ribosome ready for next aminoacyl tRNA 5¢ GTP LE 17-18 2 2 GDP E E P A P A GDP GTP E P A

  23. 4. Termination • When a “STOP” codon (UGA, UAA, UAG) is reached on the mRNA, there isn’t a complementary tRNA so…. • UGA = UGo Away • UAA= UAre Awesome • UAG= UAre Great

  24. 4. Termination • A “release factor” binds to the “A” site • Causes the addition of a water molecule to the polypeptide which hydrolyzes the completed polypeptide from the tRNA • Ribsomal subunits dissociate (break apart from the mRNA) • Newly formed protein goes to rough ER for modification, then to golgi for packaging then released from cell (exocytosis)

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