FCH 532 Lecture 18. Exam on Friday, Mar. 19 Extra Credit due on Friday Chapter 31: RNA processing. Messenger RNA splicing. A pulse-chase experiment. Pulse-chase labeling studies indicated two important characteristics of eukaryotic RNA:
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Exam on Friday, Mar. 19
Extra Credit due on Friday
Chapter 31: RNA processing
A pulse-chase experiment
+ 32P phosphate for
30 seconds (“pulse”)
+31P for 10 minutes (“chase”)
Anneal, shadow with heavy metals,
analyze in EM
Intron sequences not present in
Interpretation of the EM image:
1. The 3’-OH group of the guanosine forms a phosphodiester bond with the intron’s 5’ end, liberating the 5’ exon.
2. The terminal 3’-OH group of 5’ exon forms a phosphodiester bond with the 5’ terminal phosphate of the 3’ exon-this splices together the two exons and releases the intron.
3. The 3’-terminal OH group of the intron forms a phosphodiester bond with the phosphate of the nucleotide 15 residues form the intron’s 5’ end, yielding the 5’-terminal fragment with a cyclized intron.
Figure 32-2 Base pairing by the adenine analog 2-aminopurine. It normally base pairs with thymine (a) but occasionally also does so with cytosine (b).
Figure 32-3 Oxidative deamination by nitrous acid.(a) Cytosine ® uracil, which pairs with A.(b) Adenine ® hypoxanthine, which pairs with C.
Figure 32-7The adaptor hypothesis. It postulates that the genetic code is read by molecules that recognize a particular codon and carry the corresponding amino acid.