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Protein Synthesis

Learn how DNA is transcribed into mRNA and then translated into proteins. Understand the stages, components, and significance of protein synthesis. Explore mutations and their impact on protein production.

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Protein Synthesis

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  1. Protein Synthesis Transcription and Translation Mader Biology Chapter 14

  2. Protein synthesis = Central dogma= DNA To RNA TO protein Transcription: DNA transcribes code to mRNA in nucleus Translation: tRNA transports amino acids to mRNA on ribosome, builds polypeptide

  3. 3 rna’s used to make proteins • mRNA – carries the “message” of DNA • Travels from nucleus to cytoplasm • Takes message to ribosome for protein synthesis • tRNA – transfer RNA – brings amino acids to ribosome for protein synthesis • rRNA – ribosomal RNA – what ribosome is made of

  4. Amino acid attachment site A A G 3 5 Anticodon Symbol used in some books The tRNA molecule

  5. Nuclear envelope DNA TRANSCRIPTION DNA TRANSCRIPTION mRNA Ribosome Pre-mRNA RNA PROCESSING TRANSLATION mRNA Polypeptide Ribosome (a) TRANSLATION Polypeptide (b) Transcription and translation • In eukaryotes, separated by nuclear envelope • In prokaryotes, occurs together

  6. transcription DNA mRNA

  7. Non-template strand of DNA Elongation RNA nucleotides RNA polymerase T A C C A T A T C 3 U 3 end T G A U G G A G A C C C T A 5 A A T A G G T T Template strand of DNA 5 Direction of transcription (“downstream”) Newly made RNA Transcription • Transfer of genetic information from DNA to RNA (mRNA) • Similar to replication: • The DNA strands must separate • Nitrogen bases are paired with their opposite • Unlike replication: • Carried out by RNA polymerase (not DNA polymerase) • Only 1 mRNA strand created, not 2 • Leading strand only • Thymine  Uracil

  8. More Transcription • Promoter- region where RNA polymerase attaches and initiates transcription • Often a sequence of TATA – known as the TATA box • Terminator- DNA sequence that signals the end of transcription

  9. transcription DNA mRNA

  10. 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 U C Codons 5 3 mRNA Translation • mRNA  protein • Takes place on ribosome in cytoplasm • Video here

  11. Translation: Genetic Information is “read” • DNA = letters A, C, T, G (you know this!) • These bases are encoded as a sequence base triplets, or codons, each of which is translated into a specific amino acid • FOR EXAMPLE: • Theredfoxatetherat = the red fox ate the rat • AUGCCTUGUCGA = AUG CCT UGU CGA (easier, huh?)

  12. Translation: Genetic information is “read” • Codons = genetic code • Translates to amino acids (proteins) • Codon chart is universal for all living organisms (see pink sheet) • So, let’s take the DNA sequence: • TACGGT • mRNA sequence? • Amino acid sequence? • *see chart

  13. How does translation happen?3 stage process

  14. 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 Small ribosomal subunit Translation initiation complex 1) Initiation • 1) Initiation • Brings together mRNA, tRNA and ribosome • Begins at the start codon, AUG

  15. Amino end of polypeptide 1 Codon recognition DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide E mRNA 3 Ribosome ready for next aminoacyl tRNA P A site site 5 GTP 2 GDP 2 E E P A P A 2 GDP Peptide bond formation Translocation. 3 GTP E P A 2) Elongation • Codon of mRNA and anticodon of tRNA complementary bond to one another • Peptide bond formation • Translocation-ribosome moves to next codon

  16. Release factor Free polypeptide 5 3 3 3 5 5 Stop codon (UAG, UAA, or UGA) The release factor hydrolyzes the bond between the tRNA in the P site and the last amino acid of the polypeptide chain. The polypeptide is thus freed from the ribosome. When a ribosome reaches a stop codon on mRNA, the A site of the ribosome accepts a protein called a release factor instead of tRNA. The two ribosomal subunits and the other components of the assembly dissociate. 2 1 3 3) Termination • mRNA stop codons - UAA, UAG, UGA

  17. Protein synthesis and mutation • Mutation = Permanent, (sometimes) heritable DNA change • Mutagens: • Chemical mutagens (alcohol, tobacco, drugs) • Increases rate to 1 in 1000-100,000) • Radiation • X rays, gamma rays break DNA, bases • UV light causes knots in DNA strand • Spontaneous mutations • Occurs in DNA replication (1 in 109 bp) • Polymerase makes mistakes

  18. Protein Synthesis and Mutation • Point mutation (base substitutions) • Can have many effects: • Missense mutation • Nonsense mutation • Run-on • Silent mutation • Frameshift mutations (Insertions or deletions) • Dramatic change in amino acids • Run-ons, premature stops (nonsense mut.)

  19. Point Mutation - Substitutions • A substitution of one base for another This can have many different effects: • Missence • Nonsense • Run-on • Silent

  20. Missense mutation • Changes an amino acid in the sequence

  21. Nonsense mutation • Prematurely stops the amino acid sequence

  22. Run-on mutation • Continues the sequence that was supposed to end G C Glu

  23. Silent mutation • No effect on the amino acids G C

  24. Frameshift Mutations – Insertions or deletions THEBIGCATATETHERAT = THE BIG CAT ATE THE RAT THEBIGCBATATETHERAT = THE BIG CBA TAT ETH ERA T

  25. Summary: Mutations POINT mutations-one base pair is changed • Substitutions FRAMESHIFT: • Insertions (additions) • Deletions

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