RNA | Anatomy2Medicine
RNA

RNA

 

  • DNA/RNA/protein synthesis direction
  • DNA and RNA are both synthesized 5′ → 3′.

 

    • The 5 end of the incoming nucleotide bears the triphosphate (energy source for bond).
      • The triphosphate bond is the target of the 3 hydroxyl attack.

 

  • Drugs blocking DNA replication often have modified 3′ OH, preventing addition of the next nucleotide (“chain termination”).
  • Protein synthesis is N-terminus to C-terminus.
  • mRNA is read 5′ to 3′.
  • Start and stop codons
  • mRNA start codons

 

        • AUG (or rarely GUG).
        • Remember : AUG inAUGurates protein synthesis

 

  • Eukaryotes : Codes for methionine, which may be removed before translation is completed.

 

        • Prokaryotes : Codes for formylmethionine (f-met).

 

  • mRNA stop codons
  • UGA, UAA, UAG.
  • UGA = U Go Away.
  • UAA = U Are Away.
  • UAG = U Are Gone.
  • Functional organization of a eukaryotic gene
  • Regulation of gene expression
  • Promoter

 

        • Site where RNA polymerase and multiple other transcription factors bind to DNA upstream from gene locus (AT-rich upstream sequence with TATA and CAAT boxes).

 

  • Promoter mutation commonly results in dramatic decrease in level of gene transcription.
  • Enhancer

 

        • Stretch of DNA that alters gene expression by binding transcription factors.
        • Enhancers and silencers may be located close to, far from, or even within (in an intron) the gene

 

  • Silencer

 

      • Site where negative regulators (repressors) bind. whose expression it regulates.

 

  • RNA polymerases
  • Eukaryotes

 

        • RNA polymerase I makes rRNA (most numerous RNA, rampant).
        • RNA polymerase II makes mRNA (largest RNA, massive).
        • RNA polymerase III makes tRNA (smallest RNA, tiny).
        • No proofreading function, but can initiate chains.

 

  • RNA polymerase II opens DNA at promoter site.
  • I, II, and III are numbered as their products are used in protein synthesis.

 

        • α-amanitin, found in Amanita phalloides (death cap mushrooms), inhibits RNA polymerase II.
        • Causes severe hepatotoxicity if ingested.

 

  • Prokaryotes
  • 1 RNA polymerase (multisubunit complex) makes all 3 kinds of RNA.