1. 1 TRANSCRIPTION AND TRANSLATION

2. 2 Central Dogma of Gene Expression

3. 3 1.Important Features a. DNA contains genetic template" for proteins. b. DNA is found in the nucleus c. Protein synthesis occurs in the cytoplasm - ribosome. d. "Genetic information" must be transferred to the cytoplasm where proteins are synthesized.

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5. 5 The Genetic Code 1.A triplet code comprised of three nucleotide bases in a sequence. 2.How many triplet codes? 20 common amino acids in a protein 4 diff. bases on DNAA,T,C, & G | | | | 4 diff. bases on RNAU,A,G, & C 4 things put together in combinations of 3 = 4 3 = 64 Therefore - 64 different DNA triplet codes or RNA codons

6. 6 Genetic Code Genetic code consists of a series of information blocks called codons. – Triplet Codon and non overlapping  each codes for one amino acid  genetic code is nearly universal  UGA….tryptophan in mamalian mitochondria  AGA….terminal code in mamalian mitochondria  AGA…serin in drosophila mitochondria  Degeneracy of Genetic code

7. 7 The 64 triplet codes 60 code for amino acids 4 act as "stop" and "start codes Degenerate Code- more than one triplet code for some amino acids e.g.,

8. 8 2. Processes of Protein Synthesis a. Transcription - genetic template for a protein is copied and carried out to the cytoplasm b. Translation - template serves as a series of codes for the amino acid sequence of the protein

9. 9 Transcription RNA polymerase – only one of two DNA strands (template or antisense strand) is transcribed – non-transcribed strand is termed coding strand or sense strand same as RNA (except T’s are U’s) – In both bacteria and eukaryotes, the polymerase adds ribonucleotides to the growing 3’ end of an RNA chain.  synthesis proceeds in 5’  3’ direction

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11. 11 U C G U U C A A A mRNA A G C TTC A A A T G C AA T TG T template Strand

12. 12 A view of transcription Fig. 14.12 Brum

13. 13 Transcription Bubble

14. 14 3. Steps of Transcription - overview a. DNA unwinds b. One side of DNA "codes for a protein" c. Genetic code of DNA is a triplet code of 3 nucleotides or bases d. Each triplet is specific for the coding of a single amino acid e. Sequence of triplet codes on DNA will specify the amino acid sequence on the protein f. Major step is the synthesis of the coded "messenger" molecule – mRNA g. mRNA is "transcribed" from DNA by complementary base pairing (mRNA has no thymine, which is replaced by uracil) h. mRNA passes out to cytoplasm to the ribosome

15. 15 Transcription Elongation – Transcription bubble moves down DNA at constant rate leaving growing RNA strands protruding from the bubble. Termination – Stop sequences at the end of the gene cause phosphodiester bond formation to cease, transcription bubble to dissociate, and RNA polymerase to release DNA.

16. 16 Termination of Transcription Simple Termination GC rich Reigon Hairpin Shape (Palindromic Sequences) Nusa Tau Rho Termination Factor

17. 17 Cells Use RNA to Make Protein The RNA Players – mRNA, rRNA, tRNA During polypeptide synthesis, ribosomal RNA (rRNA) is the site of polypeptide assembly. – Transfer RNA (tRNA) transports and positions amino acids. – Messenger RNA (mRNA) directs which amino acids are assembled into polypeptides. Central Dogma – DNA  RNA  Protein

18. 18 RNA roles Messenger RNA (mRNA) – Encodes protein sequences Transfer RNA (tRNA) – Adaptor between mRNA molecules and amino-acids (protein building blocks) Ribosomal RNA (rRNA) – Part of the ribosome, a machine for translating mRNA to proteins...

19. 19 Transcription Eukaryotic transcription differs from prokaryotic transcription: – three RNA polymerase enzymes – initiation complex forms at promoter – RNAs are modified after transcription

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21. 21 Transfer RNA Anticodon: matches a codon (triplet of mRNA nucleotides) Attachment site: matches a specific amino-acid

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23. 23 Transcription and translation in eukaryotic cells are separated in space and time. Extensive processing of primary RNA transcripts in eukaryotic cells.

24. 24 RNA Editing

25. 25 Spliced Gene Transcripts DNA sequence specifying a protein is broken into segments (exons) scattered among longer noncoding segments (introns). Initially, primary RNA transcript is produced for the entire gene. – Small nuclear ribonuclearproteins (snRNPs) associate with proteins to form spliceosomes.  Lariat forms, excising introns and splicing exons to form mature mRNA.  alternative splicing

26. 26 RNA Splicing During RNA processing, intron sequences are cut out of primary transcript before it is used in polypeptide synthesis. – remaining sequences are not translated  remaining exon sequences are spliced together to form final processed mRNA

27. 27 2. Processes of Protein Synthesis a. Transcription - genetic template for a protein is copied and carried out to the cytoplasm b. Translation - template serves as a series of codes for the amino acid sequence of the protein

28. 28 Translation Start and stop signals – start signal coded by AUG codon – stop signal coded by one of three nonsense codons: UAA - UAG - UGA Initiation – Polypeptide synthesis begins with the formation of an initiation complex.  initiation factors

29. 29 Translation Begins when initial portion of mRNA molecule binds to rRNA in a ribosome – tRNA molecule with complimentary anticodon binds to exposed codon on mRNA  some tRNA molecules recognize more than one codon

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36. 36 Differences Between Prokaryotic and Eukaryotic Gene Expression Most eukaryotic genes possess introns. Individual bacterial mRNA molecules often contain transcripts of several genes. Eukaryotic mRNA molecules must be completely formed and must pass across the nuclear membrane before translation. In prokaryotes, translation begins at the AUG codon preceded by a special nucleotide sequence.

37. 37 Differences Between Prokaryotic and Eukaryotic Gene Expression Eukaryotic mRNA molecules have introns cut out and exons joined together before translation. Eukaryotic ribosomes are larger than prokaryotic ribosomes.

38. 38 Translation Source: Alberts et al

39. 39 Translation Source: Alberts et al

40. 40 Translation Source: Alberts et al

41. 41 Translation Source: Alberts et al

42. 42 Protein Structure Proteins are poly-peptides A typical proteins consists of 70-3000 amino- acids Proteins fold into secondary structure: – helices & sheets These components then fold onto each other to form tertiary structure This structure is (mostly) determined by the sequence of amino-acids that make up the protein

43. 43 Protein Structure

44. 44 Evolution Related organisms have similar DNA – Similarity in sequences of proteins – Similarity in organization of genes along the chromosomes Evolution plays a major role in biology – Many mechanisms are shared across a wide range of organisms – During the course of evolution existing components are adapted for new functions

45. 45 Evolution Evolution of new organisms is driven by Diversity – Different individuals carry different variants of the same basic blue print Mutations – The DNA sequence can be changed due to single base changes, deletion/insertion of DNA segments, etc. Selection bias