Protein Synthesis Biology 11 preAP

1. Protein SynthesisBiology 11 preAP Overview and Application

2. Try This! • 1) One strand of DNA has the following sequence: T A C C G A C G GWhat is the corresponding sequence of RNA? • 2) If this new RNA is transported out of the nucleus directly to a ribosome, which of the three types of RNA is it?

4. OverviewMolecular Biology’s central dogma: replication, transcription, translation, assembly: Howard Hugh’s Medicalhttp://www.youtube.com/watch?v=D3fOXt4MrOM It is expected that you will know: • The key terms gene expression, transcription, and translation. • How to explain the process of transcription • How eukaryotic cells modify RNA after transcription • The steps to translation • How point mutations can change the amino acid sequence

5. Overview • What are the stages of Protein Synthesis? • Transcription • mRNA Processing and Modification • Translation

7. Transcription • DNA is used as a template to form a molecule of single-stranded mRNA (messenger RNA) • http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm

8. Transcription Three steps:1) DNA unzips 2) Complimentary base pairing of ribonucleotides 3) Termination

9. Transcription – 1) Unzip • One section of DNA is unzipped (H-bond between nitrogen bases are broken) when RNA polymerase attaches to the promotor region of the DNA with the assistance of transcription factors. • Transcription Initation Complex • The DNA continues to be unzipped by RNA polymerase

10. Transcription – 2) Complimentary • RNA polymerase attatches free-floating ribonucleotides in the 5’-3’ direction • temporarily hydrogen bond with their complimentary nucleotides on the DNA transcription unit • Covalent bond to the 3’ end of the previous ribonucleotide • Only one of the DNA strands is used as the template. • Ex: DNA – A T C G RNA –

11. Transcription - Termination • RNA polymerase reaches terminator sequence • RNA polymerase detaches from DNA, releasing single-stranded RNA strand • DNA rewinds into its double helix

13. mRNA Processing • http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/movie-flash.htm • Addition of 5’ cap • Addition of poly-A tail • RNA splicing • Introns are removes, exons are spliced together by an enzyme called spliceosome • This enzyme has small nuclear RNA (snRNA) to help it work and is therefore referred to as a riboenzyme • Modified mRNA is transported out of the nucleus

15. Significance of mRNA splicing… • We have fewer than 25000 genes to make ~100000 proteins! • One gene can make different proteins due to alternative mRNA splicing.

17. Translation • mRNA goes to the ribosome and is used as a template to synthesize a protein molecule. • http://vcell.ndsu.nodak.edu/animations/translation/movie.htm

18. Translation Three Steps: 1) Initiation 2) Elongation 3) Termination

19. Translation – 1) Initiation • need start codonAUG • The first tRNA, with anticodon UAC and amino acid methionine temporarily binds to the first site

20. Translation – 2) Elongation • The second tRNA molecule attaches to the second site of translation.

21. Translation – 2) Elongation • The amino acid from the first tRNA is transferred to the amino acid on the second tRNA.

22. Translation – 2) Elongation • The first tRNA exits, the ribosome moves, a new tRNA enters, and the process is repeated.

23. Translation – 2) Elongation • The process is repeated many times, and a peptide, or strand of amino acids, is formed.

25. Translation – 3) Termination • The release factor enters. • Translation, or protein synthesis, ends.

26. Translation – 3) Termination • The completed polypeptide is released.

27. Translation - Application • What does this diagram represent? - Translation - ELONGATION

28. Polyribosomes • Many ribosomes transcribing the same mRNA • Very efficient!

29. Destination of Proteins • How does a protein “know” whether it to be used for a function in the cell, or bound for secretion? • Signal peptide: the first ~20 amino acids directs the final destination

31. Application – table of mRNA codons (p 511)

32. Application • Consider the following DNA base sequence read from left to right: T A C G C A A A A T G G • Determine the amino acid sequence that results from this DNA strand.

33. Application • DNA sequence: T A C G C A A A A T G G • mRNA sequence: A UGC G U U U U A C C • Animo acid sequence: methionine – arginine – phenylalanine – threonine

34. Application Which of the following is an anticodon of a molecule of tRNA carrying glycine? A. G G A B. C C U C. C C T D. C G C

35. Application Which of the following is an anticodon of a molecule of tRNA carrying glycine? Amino acid: glycine mRNA codon: GGU/GGC/GGA/GGG tRNA anticodon: CCA/CCG/CCU/CCC

36. Application Which of the following is an anticodon of a molecule of tRNA carrying glycine? A. G G A B. C C U < ANSWER! C. C C T D. C G C

37. Mutation Definitions • point mutation: • A change in the sequence of a base pair within a gene • Base-pair substitution • Missense mutation – still amino acid • Nonsense Mutation – code for stop • Insertion and deletion – can cause frameshift mutation!

38. Definitions – Gene Mutations • frameshift mutationsTHE CAT ATE THE RAT – what if the “C” was deleted? • The original DNA coded for which amino acids? • DNA: TAC GGT TAG • mRNA: AUG CCA AUC • amino acids: methionine – proline - isoleucine • The mutated DNA now codes for which amino acids? • DNA: TAC CGG TTA G • mRNA: AUG GCC AAU C • animo acids: methionine – alanine - asparagine

39. Definitions - Gene Mutation • What effect does changing the amino acids have on the protein product? • Changes the shape. Since shape determines function, it alters how the protein will function.

40. Proteins: Shape determines Function!

41. Definitions - Gene Mutation • Which has the potential for the most damage, deletions or subsitituations? • Deletions! Frameshift

42. Definitions • Mutagens • Environmental influences that cause mutations • Examples: Radiaton: radioactive elements, ultraviolet (UV) light, X rays Organic chemicals: cigarette smoke, pesticides

43. Any Questions?

44. Closing • http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm • http://vcell.ndsu.nodak.edu/animations/translation/movie.htm • http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/movie-flash.htm • Molecular Biology’s central dogma: replication, transcription, translation, assembly: Howard Hugh’s Medicalhttp://www.youtube.com/watch?v=D3fOXt4MrOM • Epic:http://www.youtube.com/watch?v=u9dhO0iCLww