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PROTEIN SYNTHESIS

PROTEIN SYNTHESIS. THE DETAILS. We already know about DNA Replication. Making RNA from DNA. Transcription. RNA. Pg 251. Comparing DNA & RNA. Pg 251. RNA. Different types of RNA All are produced from a DNA template in the nucleus Classified according to their function in the cell.

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PROTEIN SYNTHESIS

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  1. PROTEIN SYNTHESIS THE DETAILS

  2. We already know about DNA Replication

  3. Making RNA from DNA Transcription

  4. RNA Pg 251

  5. Comparing DNA & RNA Pg 251

  6. RNA • Different types of RNA • All are produced from a DNA template in the nucleus • Classified according to their function in the cell

  7. Types of RNA

  8. DNA Template Strand Transcription mRNA Translation Protein A T G G A C T T A 5’ 3’ 5’ U A C C U G A A U 3’ Amino acid Amino acid Amino acid

  9. TRANSCRIPTION: the details INITIATION • RNA polymerase binds to promoter (sequence of DNA upstream of the gene to be transcribed) – opens up the double helix • promoters contain base pair patterns rich in A’s and T’s ….Why???

  10. RNA polymerase binds to DNA at promoter region

  11. DNA strand is unwound, double helix disrupted…exposing template strand

  12. ELONGATION • RNA polymerase starts building mRNA in the 5’ to 3’ direction • process similar to DNA replication – except… • no primer is used • only 1 strand of DNA is used -the template strand or the antisense strand

  13. DNA template is used to synthesize mRNA in 5’ to 3’ (uracil complements adenine)

  14. DNA that has already been transcribed rewinds into double helical form

  15. ELONGATION • unused DNA strand is called the coding strand or the sense strand ***mRNA is complementary to the template strand and identical to the coding strand (except it contains U)

  16. TERMINATION • Specific nucleotide sequences in the template serve as a signal to stop transcription • mRNA dissociates from the DNA template • RNA polymerase is free to transcribe another gene.

  17. RNA polymerase reaches termination sequence at end of gene.

  18. RNA synthesis ceases; mRNA and RNA polymerase are released

  19. mRNA MODIFICATIONS in Eukaryotes • Convert precursor mRNA (pre-mRNA) to mature mRNA 1) 5’ cap added • 7-methyl guanosine added to 5’ end • Cap is recognized by the protein synthesis machinery

  20. Pg 255

  21. mRNA MODIFICATIONS in Eukaryotes 2) Poly-A tail added • The addition of a series of A nucleotides to the 3’ end of the pre-mrNA • Makes mRNA more stable, allows it to exist longer in cytoplasm animation

  22. Pg 255

  23. mRNA MODIFICATIONS in Eukaryotes 3) Introns cut out • eukaryotic genes have coding regions called exons, and non-coding regions called introns • Splicing – intron sequences are removed and the exons are joined together to form the mature mRNA

  24. mRNA MODIFICATIONS in Eukaryotes 3) Introns cut out • snRNP’s (particles of snRNA and protein) recognize regions where exons and introns meet, and bind to those areas • snRNP’s interact with other pr- forming a larger spliceosome complex that removes introns

  25. mRNA MODIFICATIONS in Eukaryotes 3) Introns cut out • for the expression of most genes, all of the exons are spliced together • BUT, sometimes only certain exons are used to form a mature RNA transcript (alternative splicing)

  26. mRNA MODIFICATIONS in Eukaryotes 3) Introns cut out • Alternative splicing allows for one gene to code for more than one protein • Certain cell types are able to produce forms of a pr- that are specific for that cell

  27. Unlike DNA replication, no quality control in mature RNA, therefore, there are more errors made during transcription than DNA replication….BUT…

  28. Since a single gene is transcribed many times to produce 100’s of transcripts, errors are not as detrimental. • Errors in mRNA result in a protein being made that is susceptible to degradation.

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