NBME 24 Post-translational modification (NBME Answers)

NBME 24 Answers ↦

nbme24/Block 1/Question#31 (49.5 difficulty score)
An experimental study is conducted to examine ...
Post-translational modification🔍
tags:

+8
submitted by boostcap23(32),

Even if you didn't know anything about the gene mentioned they tell you the PROTEIN serves as a precursor for making the hormones thus it has already undergone translation and the only choice that makes sense is Post-translational modification. Additionally, mRNA means it has already undergone splicing and post-transcriptional modification as it would be called hnRNA otherwise. (FA2020 pg 41)

+6
submitted by nor16(57),

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OPCM si a neprmrohoo pieetdp ncah.i

tI si nerdstalat dan lreta zeneyms ctu tsih deipetp in eht iupbep.dstse

tnniaocpiTrrs si rognw (i hda hsit to.o).. /cb tsi tno hte NmAR htta akmse dtrefnfie teiepdp no.eshrom ovMoe,rre atwh I ees nwo ,is atht srtaolstnitpnpiorca omfnciodaiit si more ro ssel .cnp.sgl.ii so a-potttla.rnss dfiaitmoc.noi xnte itme ew eakm ti cterocr -;)

medguru2295 This is a perfect explanation. I never knew it was the protein modified (I initially though alternate splicing too) +1

nerdstewiegriffin Is this an example of polycistronic mRNA? +

paperbackwriter @nerdstewiegriffin possibly (because it says that the original mRNA results in proteins plural, BUT the mechanism for POMC derived hormones specifically is not bc of polycystronic mRNA. Polycystronic means that you get multiple protein products from one mRNA, but in this case we get multiple PROTEIN DERIVATIVES from one PROTEIN, implying that there are some modifications/reactions taking place once we've already made ONE protein which change the protein into multiple diff. products. +1

+3
submitted by link981(156),

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sreoydwK rmfo D.r oucrT orfm lna:aKp

niaRlpieco-t NAD
Trnincoptrai-s RAN
sonaTna-ilrt Prnotie

hungrybox bruh this is like bio 101 lol +7

+1
submitted by medstruggle(12),

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hWy si terevaatiln lncgipis or ntostpprinar-liaocts nitimoodfaci o?tcicrenr

tea-cats-biscuits You just have to know that POMC is a pro-protein that must be cleaved; not sure if there’s anything in the stem that would really have given it away. +2

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. +31

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. +1

medschul They're cleaved by tissue-specific proteases +1

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. +6

tadki38097 Just general testing taking strategy i guess, but for this question i was torn between post-transcriptional and post-translational, but then i saw that alternative splicing was also a choice...because alternative splicing IS a post-transcriptional modification you know it has to be post-translational because you can't select two answer choices. +1

+1
submitted by suckitnbme(164),

POMC is a prohormone peptide chain that gets cleaved into gamma-MSH, ACTH, gamma-lipotropin, and beta-endorphin. There's a nice figure of this in Costanzo (Fig 9-10).

It may help to remember that pathologies with increased ACTH (ie Addison's disease) can present with hyperpigmentation since MSH (melanocyte stimulating hormone) is produced alongside ACTH.

hungrybox https://classconnection.s3.amazonaws.com/1442/flashcards/861876/jpg/picture11-thumb400.jpg Here's the figure +

+0
submitted by asharm10(22),

It's saying a particular protein is made from this mrna, this protein is used as a precursor to produce those two hormones. so proteins once made, they need post translational trimming of N and C propeptides to be active. like trypsinogen becomes trypsin else they are just inactive protein. So any protein to work they need to go through post translational modifications.

+0
submitted by alienfever(5),

So if a long polypeptide string is generated from signle mRNA then cleaved → post-translational modification.

If modification happens at level of RNA which is cleaved into smaller mRNA that then give proteins → alternative splicing / post-tranSCRIPTIONAL modification.