DNA makes RNA makes Proteins. The Central Dogma

Transcription

1 DNA makes RNA makes Proteins The Central Dogma

2 TRANSCRIPTION DNA RNA transcript RNA polymerase RNA PROCESSING Exon RNA transcript (pre-mrna) Intron Aminoacyl-tRNA synthetase NUCLEUS CYTOPLASM FORMATION OF INITIATION COMPLEX Amino acid trna AMINO ACID ACTIVATION A mrna Growing polypeptide Activated amino acid E P Ribosomal subunits TRANSLATION E A Anticodon Codon Ribosome

3 The Central Dogma DNA makes RNA makes Proteins

4 Transcription DNA --> RNA requires RNA polymerase enzyme three types (in Euk) [IB: you don t need to know the differences] RNAp II makes mrna RNAp extends new RNA in 5-3 (other RNA types in mito, chloro) reads template strand DNA 3 -> 5 adds nucleotides to the 3 end of growing RNA Initiation, Elongation, Termination...

5 Transcription Initiation In euk, initiation factors mediate RNAp binding after RNAp binds: transcription initiation complex How does the RNAp know which strand to copy? RNAp attaches to a promoter region Elongation dbl helix re-bonds upstream of RNAp multiple RNAp mols can operate on same gene at same time Termination RNAp stops at end of terminator

6 Topic 7.2: Transcription and Gene Expression Understandings (overview) 1.Transcription occurs in a 5 to 3 direction 2.Nucleosomes help to regulate transcription in eukaryotes 3.Eukaryotic cells modify mrna after transcription 4.Splicing of mrna increases the number of different proteins an organism can produce 5.Gene expression is regulated by proteins that bind to specific base sequences in DNA 6.The environment of a cell and of an organism has an impact on gene expression

7 Topic 7.2: Transcription and Gene Expression Understandings: 1.Transcription occurs in a 5 to 3 direction nucleoside triphosphates (NTPs) line up opposite their complementary base partner RNA polymerase covalently binds the NTPs (releasing the two additional P) The 5 -phosphate links to the 3 -end of the growing mrna strand THUS: transcription occurs in a 5 3 direction

8 Topic 7.2: Transcription and Gene Expression Understandings: 2.Nucleosomes help to regulate transcription in eukaryotes media: Inheritance, pt 1 & 2 (Radiolab) Methylation Acetylation Adding an acetyl group to the tail neutralizes charge = DNA less tightly coiled and increasing transcription Adding a methyl group to the tail maintains positive charge = DNA more coiled and reducing transcription

9 Topic 7.2: Transcription and Gene Expression Understandings: 3.Eukaryotic cells modify mrna after transcription Three processes: Capping methyl group added to the 5 -end protection against exonucleases ribosome attachment Poly-A tail long chain of adenine nucleotides to the 3 -end helps export from the nucleus splicing introns removed ( intervening introns ) exons fused ( expressed exons")

10 Topic 7.2: Transcription and Gene Expression Understandings: 4.Splicing of mrna increases the number of different proteins an organism can produce

11 Topic 7.2: Transcription and Gene Expression Understandings: 5.Gene expression is regulated by proteins that bind to specific base sequences in DNA Activator proteins bind to enhancer sites Repressor proteins bind to silencer sites

12 Topic 7.2: Transcription and Gene Expression Understandings: 6.The environment of a cell and of an organism has an impact on gene expression

13 Topic 7.2: Transcription and Gene Expression Types of Chromatin: Some DNA = permanently supercoiled, some changes over the life cycle of the cell

14 Topic 7.2: Transcription and Gene Expression Types of Chromatin: Some DNA = permanently supercoiled, some changes over the life cycle of the cell

15 Topic 7.2: Transcription and Gene Expression Understandings: 6.The environment of a cell and of an organism has an impact on gene expression

16 Topic 7.2: Transcription and Gene Expression Skill: Analyze changes in methylation pattern

17 Topic 7.2: Transcription and Gene Expression Skill: Analyze changes in methylation pattern

18 LE 17-7b Elongation RNA polymerase Non-template strand of DNA RNA nucleotides end Direction of transcription ( downstream ) Template strand of DNA Newly made RNA

19 LE 17-7a-1 Promoter Transcription unit Start point DNA RNA polymerase

20 LE 17-7a-2 Promoter Transcription unit Start point RNA polymerase DNA Initiation Unwound DNA RNA transcript Template strand of DNA

21 LE 17-7a-3 Promoter Transcription unit Start point RNA polymerase DNA Initiation 5 Unwound DNA RNA transcript Template strand of DNA Elongation 5 Rewound DNA 5 RNA transcript

22 LE 17-7a-4 Promoter Transcription unit 5 Start point RNA polymerase DNA Initiation 3 Unwound DNA RNA Template strand tran- of DNA script Elongation Rewound DNA RNA transcript Termination Completed RNA transcript

23 RNA editing in prok: transcript is translated directly (except trna, rrna) in euk: modifications in nucleus 5 cap added (modified G) 3 end gets poly-a-tail A-nucleotides

24 RNA editing, cont d in cytoplasm: RNA splicing avg transcript = 10,000bp. Avg prot = 400aa. (8800bp cut!) introns cut out, exons joined cut & splice by: spliceosome = prot + small nuclear ribonucleoproteins (snrnps) ( snurps ) Protein RNA transcript (pre-mrna) Exon 1 Intron Exon 2 snrna snrnps Spliceosome Other proteins Why are introns a good thing? alternative splicing regulatory introns (mirna) Spliceosome components mrna Exon 1 Exon 2 Cut-out intron

25 LE DNA Gene Exon 1 Intron Exon 2 Intron Exon 3 Transcription RNA processing Translation Domain 3 Domain 2 Domain 1 Polypeptide

26 Translation trna is the translator process mediated by ribosome large, small subunits proteins + rrna (most abundant RNA) trna deposits a.a., codon by codon ribosome joins a.a. s into polypeptide 45 different trna s; why not 64? wobble third base in codon doesn t have to match ex: U match with A or G thus: more than one codon can code for same a.a ex: ACA, ACU, ACC, ACG all code for Thr

27 Ribosomes during initiation: start codon attracts initiator trna w/ Met sm subunit attaches to mrna sm subunit moves downstream lg subunit attaches three sites: A: holds trna w/ next a.a for growing chain P: hold trna carrying the growing chain E: ejection seat for trna ribosome = big ribozyme hydrolysis of GTP supplies E continues until stop codon reached

28 Translate this: AUG,GAG,GAA,AUA,GAU,UGA AUG,GUG,GAA,AUA,GAU,UGA AUG,GGG,AAA,UAG,AUU,GA AUG,GCA,GGA,AAU,AGA,UUG,A

29 TRANSCRIPTION DNA RNA transcript RNA polymerase RNA PROCESSING Exon RNA transcript (pre-mrna) Intron Aminoacyl-tRNA synthetase NUCLEUS CYTOPLASM FORMATION OF INITIATION COMPLEX Amino acid trna AMINO ACID ACTIVATION A mrna Growing polypeptide Activated amino acid E P Ribosomal subunits TRANSLATION E A Anticodon Codon Ribosome

30 Ribozymes RNA: more than DNA message H-bond to other nucleic acids form 3-D structure by self-bonding contains functional catalytic groups Ribozymes: def = RNA molecules catalyzing a chem rxn ribozymes catalyze their own cleavage, and even their own synthesis RNA can store, transmit, and duplicate genetic info also regulate gene expression snrna, sirna, mirna RNA nucleotides have been made spontaneously in lab Key to origin of life?

31 The End

32 DNA Review

33 DNA/RNA Review Scientists DNA structure bases nucleotides diagram DNA replication = semi-conservative RNA vs DNA RNA functions (r,t,m) transcription sense strand regulation of transcription promoter causes RNA polymerase to bind prokaryotes: introns introns/exons reverse transcriptase (Ch 18; HIV, cdna & mol bio) translation initiation, elongation, termination