RNA Polymerase. Initiation in eukaryotes. RNA processing in eukaryotes 10/25/18. Transcription and Translation. DNA is copied to make messenger RNA

Transcription

1 RNSRIPION RN PROSSING RNSLION DN Pre- 10/25/18 ranscription and ranslation Finish ranscription processing Introns and exons Other types of RN he genetic code ranslation to protein Initiation longation ermination Specificity of translation Mutations 26 Oct 2018 RN Polymerase Non-template strand of DN U New RN end G G U RN nucleotides G G U G emplate strand of DN DN is copied to make messenger RN his is the non-template strand. Note that it reads almost the same as the his is the template strand that is actually copied Both strands of DN can serve as the template Some genes are on one strand, other genes are on the other 5...GGGG GGGG ucuaaugucaaugcaà 3 RN copy DN Small segment of human genome Initiation in eukaryotes RN processing in eukaryotes 1 ukaryotic promoters box Promoter 1. dd 5 cap 2. dd poly tail to 3 end box Start point emplate DN strand 2 Several transcription RNSRIPION DN modified guanine nucleotide added to the end 50 to 250 adenine nucleotides added to the end Several transcription must bind to promoter sequences upstream of the gene hen RN polymerase can bind ranscription 3 dditional transcription RN polymerase II ranscription RN transcript ranscription initiation complex RN PROSSING RNSLION Pre- G P P P ap modified GP is added, backwards, on the 5 end UR Protein-coding segment Start codon Stop codon Polyadenylation signal U UR Poly- tail bout 200 s added at 3 end 1

2 RN processing in eukaryotes RNSRIPION RN PROSSING RNSLION DN Pre- Pre- 3. Splice out introns ap 1 xon Intron oding segment xon Intron xon Introns cut out and exons spliced together ap Poly- tail UR UR Poly- tail RN has many functions 4 main types: Messenger RN Ribosomal RN ransfer RN Small nuclear RN Folds to many possible shapes an act as an enzyme ( ribozyme ) RN can base-pair with itself to form loops. Four types of RN Messenger RN, encodes the amino acid sequence of a rrn Ribosomal RN, forms complexes with protein called ribosomes, which translate to protein trn ransfer RN, transports amino acids to ribosomes during protein synthesis snrn Small nuclear RN, forms complexes with proteins used in eukaryotic RN processing DN and RN ompared 1. RN is single stranded. 2. Sugar is different. 3. RN uses U instead of 4. RN leaves nucleus, DN doesn t. DN --> RN --> Protein he Genetic ode DN molecule Gene 2 Gene 1 Gene 3 DN strand (template) G G RNSRIPION U G G U U U G G U odon RNSLION Protein rp Phe Gly Ser mino acid 2

3 he code is a triplet code he first evidence for triplet code came from deletion experiments the neb oys awt heb igc ate att heh otd og he code is a triplet code... or by two more deletions to get it back into the correct reading frame the neb oys awt heb igc ate att heh otd og the neb osa wte big cat eat the hot dog Partial function could be restored by an insertion nearby the neb oys aaw the big cat eat the hot dog Deciphering the ode Your book tells how people used synthetic s and in vitro translation to determine decipher the codons. xamples UUUUUUUUUUU -> phenylalanine only Several different codons encode the same amino acid he code is redundant UUUUUU -> Mixture of leucine and serine Why is it a mixture? he code is comma free No punctuation between words. herefore deletions cause frameshifts It does have start and stop signals, however. Start: UG Stop: UG, U, UG ranslation: the basic concept he ribosome is the machine that builds the RNSRIPION RNSLION DN G rp Phe mino acids codon. trn with amino acid attached G U G G U U U G G Gly trn nticodon trn serves as an adaptor that brings the correct amino acid to each odons 3

4 mino cid attachment ransfer RN (trn) structure P model of a ribosome P (Peptide ) (cceptor ) (xit ) P Large nticodon binding Small New amino acids are added to the carboxyl end of the he initiation of translation Met U U G P Met Large ribosomal mino end Growing Next amino acid to be added to chain trn Initiator trn Start codon binding GP Small ribosomal ranslation initiation complex odons he ribosome assembles at the start codon (UG) longation Fig ready for next aminoacyl trn mino end of P GP 1. trn with appropriate anticodon binds at Release factor ermination Free P P Stop codon (UG, U, or UG) 3. ranslocaton. verything moves left one notch. is now at P. mpty trn leaves the. GP P 2. Peptide bond formed. Growing chain is now at Stop codon has no matching trn Release factor binds and separates the from the trn he ribosome separates from 4

5 n aminoacyl-trn synthase joins a specific amino acid to a trn n aminoacyl-trn synthase joins a specific amino acid to a trn ach trn has a slightly different shape. ach fits a different trn synthase enzyme. ach enzyme is specific to a particular amino acid and trn lananine trn synthase Other amino acids don t fit... Many drugs inhibit protein synthesis oxin Mode of action arget forms peptidyl-puromycin, prevents Puromycin translocation blocks the -, prevents binding of aminoacyl etracycline trns hloramphenicol blocks peptidyl transfer ycloheximide blocks peptidyl transferase ucaryotes Streptomycin inhibits initiation at high concentrations Diphtheria toxin catalyzes DP-ribosylation of residue in ef2 ucaryotes rythromycin binds to 50S, inhibits translocation Ricin inactivates 60S, depurinates an adenosine in 23S rrn ucaryotes NO: Prokaryotes also includes protein synthesis in mitochondria and chloroplasts Polyribosomes Figure Polysome Some types of mutations Silent Missense hange amino acid Nonsense Premature stop Frameshift Insertion or deletion changes all the rest of the codons 5