Notes- February 11

TErmination of translation- uses release factors
*GTP —> GDP fueling of aa chain formation. broke off by EF-1 alpha (or something) and EF-2.
these elongation factors are responsible for forming the peptide bonds.
*aa chain formation is only likely to happen when at least 1st 2 bases in codon / anticodon line up (base pair) correctly.
*Elongation Factors interact w/ aa's and RNAs. EF - GTP affinity for tRNA ~ 10,000x higher if tRNA bound w/ codon.

V. Termination

  • a) stop codons: codons for which there is no corresponding tRNA anticodon (UAA, UAG, UGA)
  • b) release factors (RFs). stop codons CAN interact w/ RFs. catalyze reaction that breaks bond w/ last tRNA & its aa, (after the RF binds to A site of ribosome)
  • i. in prokaryotes —> RF1 (recognizes UAA and UAG) and RF2 (recognizes stop codon UGA)
  • ii. Eukaryotes have 1 RF. it interacts w/ all three stop codons

Frameshifting:

  • addition or deletion of base
  • throws whole reading frame off past the mutation site
  • so get totally different aa sequence in protein

in ARTICLE:
programmed ribosomal frameshift (PRF) is where ribosome induces frameshift
*ribosome can interpret mRNA as multiple reading frames —> 1 protein from 1 mRNA

PRFS is a potential target for antiviral agents

RF2 transcript is only fully translated when RF2 is needed!

RF2 in prokaryotes:
E. Coli and other bacteria have gene for RF2 that recognizes stop codon. RF2 isn't necessarily expressed all the time. When does E. Coli know when to express RF2?

(RF2 transcript is only fully translated when RF2 is needed.)

- this article that was attached to an email as a pdf file WILL be on the exam.

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