Protein Synthesis

1. Protein Synthesis Chapter 17

3. Protein synthesis • DNA • Responsible for hereditary information • DNA divided into genes • Gene: • Sequence of nucleotides • Determines amino acid sequence in proteins • Genes provide information to make proteins

4. Protein synthesis DNA RNA protein

5. Protein Synthesis • Gene Expression: • Process by which DNA directs the synthesis of proteins • 2 stages • Transcription • Translation

6. Protein synthesis • Transcription: • DNA sequence is copied into an RNA • Translation: • Information from the RNA is turned into an amino acid sequence

7. Protein synthesis DNA RNA Protein Transcription Translation

10. Protein Synthesis • Central Dogma • Mechanism of reading & expressing genes • Information passes from the genes (DNA) to an RNA copy • Directs sequence of amino acids to make proteins

12. Protein synthesis • Beadle & Tatum • Bread mold • 3 enzymes to make arginine • Mutated mold’s DNA • Mutated code for enzymes • Unable to code for arginine

13. Results Table Classes of Neurospora crassa Precursor Enzyme A Wild type Class I mutants Class II mutants Class III mutants Minimal medium (MM) (control) Ornithine Enzyme B Citrulline Enzyme C MM + ornithine Arginine Condition MM + citrulline MM + arginine (control) Growth: Wild-type cells growing and dividing No growth: Mutant cells cannot grow and divide Can grow on ornithine, citrulline, or arginine Can grow with or without any supplements Can grow only on citrulline or arginine Summary of results Require arginine to grow Control: Minimal medium Gene (codes for enzyme) Class II mutants (mutation in gene B) Class III mutants (mutation in gene C) Class I mutants (mutation in gene A) Wild type Precursor Precursor Precursor Precursor Enzyme A Enzyme A Enzyme A Enzyme A Gene A Ornithine Ornithine Ornithine Ornithine Enzyme B Enzyme B Enzyme B Enzyme B Gene B Citrulline Citrulline Citrulline Citrulline Enzyme C Enzyme C Enzyme C Enzyme C Gene C Arginine Arginine Arginine Arginine

14. Protein synthesis • Beadle & Tatum • One gene one enzyme • One gene one protein • One gene one polypeptide

15. An albino racoon

16. Cracking the code • Codons (Triplet code)-mRNA • Each codon corresponds to an aa • 20 amino acids • 64 triplet codes (codons) • 61 code for aa-3 are stop codons • Wobble: • Flexible base pairing in the 3rd position • 3’ end

18. Cracking the code • Reading frame • Reading symbols in correct groupings • 1 or 2 deletions or additions • Gene was transcribed incorrectly • 3 deletions • Reading frame would shift • Gene was transcribed correctly

19. WHYDIDTHEREDCATEATTHEFATRAT WHYIDTHEREDCATEATTHEFATRAT WHYDTHEREDCATEATTHEFATRAT WHYTHEREDCATEATTHEFATRAT

20. Cracking the code • Universal code • AGA codes for amino acid Arginine • Humans & bacteria • Genes from humans can be transcribed by mRNA from bacteria • Produce human proteins • Insulin

21. RNA • RNA (ribonucleic acid) • Single strand • Sugar –ribose (-OH on 2’ carbon) • Uracil instead of thymine

24. RNA • mRNA: • Messenger RNA • Transcribes information from DNA • Codons • (3 nucleotides) CGU • mRNA • Codes for amino acids • rRNA: • Ribosomal RNA • Polypeptides are assembled

25. RNA • tRNA: • Transfer RNA • Transports aa to build proteins • Positions aa on rRNA • Anticodons • (3 complementary nucleotides) GCA

29. Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA NUCLEUS DNA TRANSCRIPTION CYTOPLASM CYTOPLASM mRNA TRANSLATION Ribosome Ribosome TRANSLATION Polypeptide Polypeptide (a) Bacterial cell (b) Eukaryotic cell

30. Transcription • Getting the code from DNA • Triplet code • Template strand • Strand of DNA • Provides template or pattern • Transcribed or read • Transcribed RNA is complementary to this DNA strand

32. Transcription • Coding strand • DNA strand not coded • Same sequence of nucleotides as the RNA transcript • Only T instead of U.

33. DNA template strand Figure 17.4 5′ 3′ C C C C G G T A A A A A T G G T T T G G C T C A 3′ 5′ TRANSCRIPTION U G G U U U G G C U C A mRNA 5′ 3′ Codon TRANSLATION Protein Gly Trp Phe Ser Amino acid

34. Transcription • RNA polymerase • Enzyme • Adds nucleotides to the 3’end • 5’to3’ direction • Does not need a primer to start • One polymerase in prokaryotes • Three in eukaryotes • Polymerase II makes mRNA

35. Transcription • Promoters: • Sequence on DNA where transcription starts • TATAAT • TATA box • Sequences are not transcribed

36. Transcription • Stages • Initiation • Elongation • Termination

37. Initiation • RNA polymerase binds promoter • Unwinds DNA • Transcription unit: • RNA polymerase, DNA & growing RNA strand

38. Fig. 17-UN1 Transcription unit Promoter 5 3 3 3 5 5 Template strand of DNA RNA polymerase RNA transcript

39. Initiation • Transcription factors bind first to the promoter in Eukaryotes • RNA pol II binds DNA • Transcription Initiation Complex is formed • Starts to transcribe

40. Promoter Nontemplate strand DNA 5′ 3′ A A A T A T A A eukaryotic promoter 1 3′ 5′ A T A T T T T TATA box Start point Template strand Transcription factors 3′ 5′ Several transcription factors bind to DNA. 2 3′ 5′ RNA polymerase II Transcription factors 5′ 3′ Transcription initiation complex forms. 3′ 3 5′ 3′ 5′ RNA transcript Transcription initiation complex

41. Elongation • RNA polymerase moves along DNA • Untwists DNA • Adds nucleotides to 3’ end

42. Nontemplate strand of DNA Elongation RNA nucleotides Fig. 17-7b RNA polymerase 3 3 end 5 Direction of transcription (“downstream”) 5 Template strand of DNA Newly made RNA

43. Termination • Prokaryotes • Stop signal • Sequence on DNA • RNA transcript signals polymerase to detach from DNA • RNA strand separates from the DNA

44. Termination • Eurkaryotes • Polyadenylation signal sequence on mRNA • AAUAAA • Recognized by RNA polymerase II • mRNA is released

45. Transcription

46. Promoter Transcription unit 3′ 5′ 3′ 5′ Start point RNA polymerase Initiation 1 3′ 5′ 3′ 5′ Template strand of DNA RNA transcript Unwound DNA Elongation 2 Rewound DNA 3′ 5′ 3′ 3′ 5′ 5′ Direction of transcription (“downstream”) RNA transcript Termination 3 3′ 5′ 5′ 3′ 3′ 5′ Completed RNA transcript

47. Eukaryotes • mRNA is modified • Nucleus • RNA processing

48. Eukaryotes • 5’ cap • Addition of a GTP • 5’ phosphate of the first base of mRNA • Methyl group is added to the GTP • 3’poly-A-tail • Several A’s on the end of the mRNA

49. Eukaryotes • Introns: • non-coding sequences of nucleic acids • Exons: • coding sequences of nucleic acids

50. Euraryotes • RNA splicing • Cut out introns • Reconnect exons • snRNP’s (small nuclear RNA’s) • Spliceosome: • Many snRNP’s come together & remove introns