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NBME 24 Answers

nbme24/Block 1/Question#31

An experimental study is conducted to examine the ...

Post-translational modification

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submitted by nor16(11),

POMC is a prohormone peptide chain.

It is translated and later enzymes cut this peptide in the subpeptides.

Transcription is wrong (i had this too...) b/c its not the mRNA that makes different peptide hormones. Moreover, what I see now is, that posttranscriptional modification is more or less splicing... so post-translat. modification. next time we make it correct ;-)

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submitted by link981(42),

Keywords from Dr. Turco from Kaplan:

  • Replication- DNA
  • Transcription- RNA
  • Translation- Protein

Why is alternative splicing or post-transcriptional modification incorrect?

tea-cats-biscuits  You just have to know that POMC is a pro-protein that must be cleaved; not sure if there‚Äôs anything in the stem that would really have given it away. +  
mcl  Dunno if this helps, but it says "this protein" (singular) is the precursor of two different protein products. This must mean that the modification occurs after the protein is made, which means after transcription and splicing has already happened. +5  
ngman  Also I believe mRNA refers to after the splicing already occurs. If the protein products are from the same mRNA then it can't be alternate splicing. +  
medschul  They're cleaved by tissue-specific proteases +  
duat98  I think: Alternative splicing occurs with hnRNA not mRNA. You get mRNA from alternatively splicing the hnRNA. an mRNA can only make 1 type of protein. Since the question says the 2 proteins comes from the same mRNA it cannot be alternative splice or post transcriptional mod. FA 2018 page 43 has a good illustration. +3