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Protein Translation

Protein Translation. From Gene to Protein Honors Biology Ms. Kim. Central Dogma. DNA  RNA  Protein Protein synthesis consists of 2 mains parts: Transcription – DNA is copied in the nucleus, the result is the formation of mRNA

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Protein Translation

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  1. Protein Translation From Gene to Protein Honors Biology Ms. Kim

  2. Central Dogma DNA  RNA  Protein • Protein synthesis consists of 2 mains parts: • Transcription – DNA is copied in the nucleus, the result is the formation of mRNA • Translation– mRNA travels to the cytoplasm and attaches to rRNA and with the help of tRNA a protein is made

  3. Translation • mRNA  polypeptide (protein)

  4. tRNA • A cell translates mRNA message into protein with help from transfer RNA (tRNA) • Type of RNA • ~80 nucleotides • “t” shape • Carries amino acids • Matches codons to anticodons

  5. Transfer RNA • Transfer RNA (tRNA) • Reads the mRNA code • Carries the amino acid that will be added to the growing protein chain • Notice the 3 bases at the bottom of the tRNA make up the anticodon • The anticodonbase pairs with the mRNA codon to make sure that each AA is delivered to the correct place on mRNA • At the top of tRNA is an amino acid

  6. tRNA • Molecules of tRNA are not all identical • Each carries a specific amino acid • Each has an specific anticodon on the other end

  7. Ribosomes • Help bind tRNA anticodons with mRNA codons during translation • Found on ROUGH Endoplasmic Reticulum RER (“bound”) or in cytoplasm (“free”) Anticodon (tRNA) = codon (mRNA)

  8. tRNA (with anticodons) mRNA (with codons)

  9. Ribosomes • There are 2 ribosomal subunits • Constructed of proteins and ribosomal RNA or rRNA

  10. Ribosomal RNA • Ribosomal RNA (rRNA) • Ribosome attaches to mRNA • Contains the enzymes necessary for protein synthesis • Ribosome: • 3 tRNA binding spots: • E – exit • P – current amino acid • A – on deck amino acid • Has a large & small subunit E P A

  11. P site (Peptide Bond-tRNA binding site) A site (Amino acid- tRNA binding site) E site (Exit site) Large subunit mRNA binding site Small subunit Binding Sites in a Ribosome • The ribosome has three binding sites for tRNA • The P site • The A site • The E site E P A

  12. Growing polypeptide Amino acid Next amino acid to be added to polypeptide chain tRNA 3 mRNA Codons 5 \

  13. What is Translation? • Process of building a protein chain by reading the mRNA code • Occurs in ribosomes • Uses codons

  14. Building a Polypeptide • Translation can be divided into 3 phases • Initiation • Elongation • Termination

  15. Initiation of Translation • initiation stage: • mRNA binds to small subunit • tRNA bearing 1st amino acid (“start”) called MET (codon AUG) comes • tRNA binds to start codon (AUG) anticodon (UAC) • Large ribosomal subunit binds  working ribosome • Initiator tRNA fits into the P site and holds the growing protein • The A site is empty and ready for the next A.A • 2 subunits of a ribosome come together

  16. Large ribosomal subunit P site 5 3 U C A Met Met 3 A 5 G U Initiator tRNA GDP GTP E A mRNA 5 5 3 3 Start codon mRNA binding site Translation initiation complex Small ribosomal subunit Figure 17.17 mRNA codons are what create the amino acids (aka – use the chart) NOT tRNA

  17. Elongation • Amino acids are added one by one to the preceding amino acid • Peptide bonds are formed Amino acid

  18. Elongation • After initiation, A.A. are added to the first A.A… • 3 step process: • 1) Incoming tRNA anticodon pairs with mRNA codon • 2) A new polypeptide bond is formed • 3) tRNA shift (P leaves, A moves to the P spot)

  19. Termination of Translation • When the ribosome reaches a stop codon on the mRNA • There are 3 stop codons • UAA, UAG, and UGA • Release factor (protein) binds to stop codon in A site (NOT tRNA)  polypeptide (protein) released

  20. Release factor Free polypeptide 5 3 3 3 5 5 Stop codon (UAG, UAA, or UGA) Termination of Translation

  21. DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide Amino acids Polypeptide tRNA with amino acid attached Ribosome Trp Phe Gly tRNA C C C G G Anticodon A A A A G G G U G U U C U 5 Codons 3 mRNA “EMPTY” tRNA Figure 17.13

  22. Polypeptide  3D Protein • Primary Structure • Amino acids is a row (LINEAR) • Secondary Structure • Amino Acids BEND and FOLD towards each other • Tertiary Structure • Amino acids BIND to each other • 3D shape made • Quartnary structure (only some) • 2 or more polypeptides BIND to each other

  23. 1 2 4 3

  24. Translation (Protein Synthesis) Animation • http://www.wisc-online.com/objects/index_tj.asp?objID=AP1302 • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html# • http://www.ucopenaccess.org/courses/APBiologyI/course%20files/multimedia/lesson13/lessonp.html

  25. Summary of Protein Synthesis • Replication→ DNA to DNA, occurs in nucleus • Transcription → DNA to RNA, occurs in nucleus • Translation → RNA to Protein, occurs in ribosome DNA  RNA  PROTEIN!

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