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Science Humor

Science Humor. THE CENTRAL DOGMA. DNA  RNA. THE CENTRAL DOGMA. Transcription & Translation . TRANSCRIPTION . TRANSLATION. Involves the copying of information from DNA into a special form of RNA called mRNA (messenger RNA) Transcribe = copy from one medium to another. .

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Science Humor

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  1. Science Humor

  2. THE CENTRAL DOGMA DNA  RNA

  3. THE CENTRAL DOGMA

  4. Transcription & Translation TRANSCRIPTION TRANSLATION • Involves the copying of information from DNA into a special form of RNA called mRNA (messenger RNA) • Transcribe = copy from one medium to another. • Involves ribosomes using the RNA as a blueprint to synthesize a protein composed of amino acids. • Translate = converting from one language to the next

  5. TRANSCRIPTION OCCURS IN THE NUCLEUS!

  6. TRANSLATION DNA  RNA

  7. TRANSCRIPTION • Can be broken down into 3 sequential processes: • 1. INITIATION • 2. ELONGATION • 3. TERMINATION

  8. OVERVIEW OF TRANSCRIPTION

  9. Transcription • Coding Strand • Template Strand • RNA Polymerase • NTPs = Nucleoside Triphosphates • RNA-DNA Hybrid Region

  10. 1. INITIATION • Enzyme RNA polymerase binds to the segment of DNA (upstream of the gene) that is to be transcribed & opens double helix. • Upstream = region of DNA near the start of a gene • This region = THE PROMOTER • Characteristic base-pair pattern: high in As & Ts. • Why?

  11. 2. ELONGATION • RNA Polymerase binds to promoter & opens helix • RNA Polymerase starts building the single-stranded mRNA in the 5’  3’ direction using one strand of DNA as a template (remember RNA has uracil instead of thymine). • Template Strand – DNA parent strand used for transcription. • Coding Strand – DNA parent strand NOT used for transcription • RNA Polymerase doesn’t need a primer to start building the complementary strand. • Elongation start as soon as it binds to the promoter!

  12. 3. TERMINATION • mRNA is synthesized until the end of the gene is reached. • RNA polymerase recognizes the end of the gene when it comes across a terminator sequence. • Newly synthesized mRNA dissociates.

  13. POST-TRANSCRIPTIONAL MODIFICATIONS

  14. POST-TRANSCRIPTIONAL MODIFICIATIONS • In eukaryotic cells, the mRNA is not ready to leave the nucleus directly following transcription. • Modifications need to made to this primary transcript into to create a mature mRNA transcript.

  15. What modifications need to be made? 1. 5’CAP ADDED 2. POLY-A TAIL 3. INTRONS EXCISED.

  16. 1. 5’CAP ADDED • A 5’ cap is added to the start of the primary transcript. • This 5’ cap consists of 7-methyl guanosine, which forms a modified guanine nucleoside triphosphate. • PURPOSE: • Protects mRNA from digestion by nucleases and phosphatases as it exits the nucleus and enters the cytoplasm of the cell.

  17. 2. POLY-A TAIL • A string of about 200 adenine ribonucleotides is added to the 3’ end by the enzyme poly-A polymerase. • “Poly-A Tail”

  18. “CAPPING AND TAILING” • 5’ CAP • 3’ TAIL

  19. 3. INTRONS EXCISED • The DNA of a eukaryotic gene comprises: • CODING REGIONS • EXONS • NONCODING REGIONS • INTRONS.

  20. Question to Class: WHAT WOULD BE THE PROBLEM WITH USING AN mRNA TEMPLATE THAT INCLUDES INTRONS?

  21. Answer… If non-coding regions were translated… • the protein would fold improperly • dysfunctional proteins.

  22. EXONS & INTRONS EXONS INTRONS SPLICEOSOME PRE-mRNA Mature mRNA

  23. INTRONS ARE REMOVED… • BEFORE the primary transcript leaves the nucleus, the introns are removed. • They are removed by SPLICESOMES (particles made up of RNA & proteins).

  24. INTRONS ARE REMOVED… • Splicesomes cut out the introns and joins the remaining exons together so that all the coding regions are now continuous. • MATURE mRNA.

  25. INTRONS ARE DEGRADED… • The MATURE mRNA transcript exits the nucleus • the spliced-out introns stay within the nucleus • they are degraded and their nucleotides are recycled.

  26. What modifications need to be made? 1. 5’CAP ADDED 2. POLY-A TAIL 3. INTRONS EXCISED.

  27. READY! READY! READY! • Once the primary transcript has been modified… • CAPPED • TAILED • INTRONS EXCISED Then… • Then… THE PROCESSED mRNA TRANSCRIPT (MATURE mRNA) IS READY TO BE TRANSLATED BY RIBOSOME INTO A PROTEIN!

  28. NO QUALITY CONTROL ENZYME • Therefore, more errors are made during transcription than during replication. • Errors in transcription are not as detrimental to the cell as those that occur during replication. • Proteins are susceptible to degradation once they are synthesized. • The correct copies of the mRNA transcript will produce adequate amounts of the required protein.

  29. Homework:Finish Package from 5.1 & 5.2READ AHEAD:5.3 - Transcription5.4 – translation Coming Up!

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