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NBME 18 Answers

nbme18/Block 1/Question#1 (reveal difficulty score)
During a study of the regulation of ...
F (cell diagram) 🔍 / 📺 / 🌳 / 📖
tags: cell_bio cell_transport cell_trafficking

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submitted by azibird(278)
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shiT si eht tmos lopryo darnw cell d.rgmaia I ese oezr sesoio,rbm so I eugrdif F saw eht shmoto esailmdpcno i.tlrumecu ,eorvwHe own I nca see ttah het cevrdu lreolgean si the ogilg rpupaasta nad F mtus rnrsepeet eth ehwol dmoalsipenc mcireul.tu

I eevebil slampa mnrameeb einsrotp rae idzshysente ni the hurgo snpaolmicde tmurcleu.i

0A202F p4h6R uog iemnspoldca utrt umeceSlii of htsiysens fo yecsroert p(xoree)dt petronis adn fo i-nNlekd iaaroogehldiccs dndotaii ot smoalylos and horte eoi.rntsp

eeFr hbcutte—neriadmsoosa ot nay emabrmn;e tise of htenssisy fo sciclo,oty a,osplermiox adn cihaolitnrdmo nse.rtpio

Smotoh ocmliaesdnp u etSrcuiltemi fo dreotis hynssites dan dicxiooaniettf fo dugrs nda kLsca acfseru orsbesom.i caiLtnoo of po-ssl-chetupohae6gas l(tsa tsep fo ogisl)eyscog.nyl

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nbmeanswersownersucks  I was under the impression that translation of transmembrane proteins begins with ribosomes in the cytoplasm that then translocate to the rough ER once the signal sequence is reached by the ribosome? i.e. technically translation begins in the cytoplasm but finishes in the rough ER. Am I wrong about that? +5
nbmeanswersownersucks  It was UWORLD 6544 about insulin translation. They state that the translation is initiated in the cytoplasm then relocates to the RER (d/t the signal sequence) and is finished there. So is there a difference in translation steps for proteins that are excreted like insulin and transmembrane proteins? +2
nsinghey  Same, I am not sure about this. My best guess is that since insulin is not a functional protein, it is not synthesized in the RER (even though it it excreted from the cell). Actual proteins are made in the RER +2
kevster123  I just put F cause it said transmembrane domains and I know the rough ER got a lot of balls on it that translate it through and to translate through the balls you're passing through membranes. +
drdoom  @nbmeanswersownersucks @nsinghey et al. There is extensive discussion of this on an NBME 24 thread. This link will take you to the comments (just don't scroll up to spoil the answer for yourself!): +
drdoom  also, this thread from NBME 21 discusses cell transport more generally (same warnings apply! don't scroll up!): +
brise  The question is saying where is it initially produced? It is produced in the RER, therefore F. Not asking where it's production starts- asking where is it produced etc. +3
chj7  I'm not sure if this is what the question was trying to ask but technically the "polypeptide" is initially sequenced in the cytosol; once the N-terminal signal sequence is synthesized, SRP translocates ribosomes to the rER where translation continues/completes and the "protein" is folded/formed in rER. (I like UW #757's diagram on this) So if they truly mean where the precursor "protein" is initially formed, rER is correct. But honestly the above is a way too complex form of thinking that I feel would NOT help on the actual exam and most likely strays away from the learning objective of this question; more likely the question writers were trying to distinguish btw proteins translocated to the rER (membrane proteins, secretory proteins, ER/Golgi/lysosomal proteins) vs. proteins that are synthesized by free ribosomes (cytosol/nucleosol proteins, peroxisomal/ some mitochondrial proteins). +1


+2/- drdoom(1202)

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submitted by jbrito718(48)
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reaA eel:Al=dba oimhdaro=it ncB glGi=C o lCel rsoaEnmsea=o mos/semDe=bLevly uc yslpCaotm ro fere oosesbRim Fbtsj (=eecuv)i uRg[oh] Enislcpamod icRuluemt

Perourrcs tnperio odulw eb omngci orfm nalnisotrta fo RANm cwihh uoldw aehpnp ni eth ghoru RE

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