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NBME 21 Answers

nbme21/Block 1/Question#17 (70.0 difficulty score)
A 7-year-old girl is brought to a clinic in a ...

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 +19  upvote downvote
submitted by usmleuser007(321),
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fI uyo oucl'ndt rerebmem which erwe ae;snesilt ehtn einaletvrta ouwdl hvae enbe ot zalreei htta niwogrg eirhncld need clsel ot vd.ieid ihsT erreiqus ADN itlaceinopr and tlat.norsnia Of hwhic eht lncceui dcia methiy is irmonttap. tI risequer a lhmyet

Tihs si wrehe oemtnienhi escmo .in enenoitMih ebisoncm iwht ATP ot rofm SMA (a emlhty nor)do

whossayin  That’s a legendary explanation. Thanks dude! +  
makinallkindzofgainz  This is exactly how I solved it! I remembered that Methionine is essential for methyl transfers, and you would need that in dividing (growing) cells. But now I'll just remember PVT TIM HaLL too :) +1  

 +15  upvote downvote
submitted by nosancuck(73),
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Yo wagd we lal ubaot PVT ITM LHLa

nhnaeianPeyll, ,elaVni tpNTD,rAKoy henirnT,oe sleoneicIu, etnei,noiMh ,nsiiedtiH cueLnie syenLi

meningitis  I don't understand what the question is asking... can someone please explain it to me? Patient doesnt eat protein, shes chubby. What does methionine have to do with this? +2  
charcot_bouchard  Just basically asking which is essential amino acids. +3  
usmleuser007  Essential amino acids (something i came up with) 1. "Three HAL fans will try meth" a. Threonine = Three b. Histidine; Arginine; Lysine = HAL c. Phenylalanine = fans d. Valine; Isoleucine; Leucine = will e. Tryptophan = try f. Methionine = meth +3  
nala_ula  They're saying there is a lack of good quality protein -> slight nutritional deficiency. She may have acquired weight but it's not because of protein. So they're specifically asking what amino acid she might be missing due to her subpar diet. Since essential amino acids are those that the body cannot make itself, out off those listed, methionine is the essential amino acid. It's on page 81 of FA 2019. +9  
nala_ula  correct me if I'm wrong please :) +  
hello  For anyone confused trying to follow @usmleuser007's comment -- slightly modified Essential amino acids mnemonic "Ah, Three fans will try meth" Ah = arginine, histidine Three = Threonine Fans (phans)= Phenylalanine Vil (Will -- German accent pronouncing English word 'will') = valine, isoleucine, leucine, lysine Try = tryptophan Meth = Methionine +1  
pg32  Why does @hello and @usmleuser007 mnemonic contain arginine? That isn't in the PVT TIM HaLL mnemonic for essential amino acids... +  
paperbackwriter  @pg32 arginine is semi-essential. It is essential in preterm infants who cannot synthesize it +  

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.1 ee"Thr HLA asnf wlli rty 
h"tme    a. erehTonni = Tereh 
    .b istdiHie;n ginn;ireA Lnyesi = LAH
    c. Pieynnalnlhae = afsn
    d. elan;iV eeoIlusnci; niuLece = 
wlil    .e hoptrTpyan = try
    .f tniheiMeon = e
pparalpha  Thanks! Good mnemonic +1  
b1ackcoffee  best mnemonic +  

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slaitnsee imoAn aisdc ()AA

)1 Alusdt eirrqeu 9 AA)( = aebl ot maek rngniae avi aeru 2)clecy nhledCir qeurrei 10 A)(A = ethy rae tlils eno3)ipdglev tWhi PUK itenosry oecbmes iaetlesns in obth ludtas nda hledrcin

 +1  upvote downvote
submitted by drzed(169),

Let's say you didn't know methionine was essential.

(A) Alanine -- you can create alanine from the enzyme ALT (alanine aminotransferase), thus this enzyme cannot be essential

(B) Aspartate -- you can create aspartate from the enzyme AST (aspartate aminotransferase), thus this enzyme cannot be essential

(C) Glycine -- this one is low yield, but it is made from serine (serine + THF -> CO2 + Me-THF + glycine). If you didn't know about this, you had a 50/50 shot

(E) Tyrosine -- you can create tyrosine from phenylalanine (unless of course you have phenylketonuria), and thus this cannot be essential.

 +0  upvote downvote
submitted by hello(246),
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roF noaney ocdsfuen rtniyg ot olflow 00@lusmsers'7ue teocmmn

tiSlhlyg modidief

inssElate maoin scadi enmonimc ",hA hreTe fsna iwll try mhette"h

Ah = ag,nnerii sdtihieni

eTrhe = ohirneneT

anFs (phs=a)n anehlnPnlaiye

illV wi(ll -- nGrame ccntae nonnorugpci gihlnEs rwdo wil")l" = vln,iae eulnsceo,ii u,liceen iyslne

yrT = athtnopypr

heMt = teonMneiih

 +0  upvote downvote
submitted by mrglass(24),

The way I remember the essential amino acids is by referencing the amino acids groups I already know. So the essential amino acids are:

  1. The branched chain amino acids: Isoleucine, Leucine, and Valine

  2. The ringed amino acids EXCEPT Tyrosine (which becomes essential in those with PKU): Tryptophan, Histidine, Phenylalanine

  3. The sulfur containing amino acids: Cysteine and Histidine (You will see debate over whether Cysteine qualifies as essential or not)

  4. The two you just have to memorize: Threonine and Lysine

mrglass  I meant to say Cysteine and Methionine* +  

 +0  upvote downvote
submitted by saqeer(2),

a little misleading her increase in weight made it seem as if she had low thyroid hormone and tyrosine is a precursor.

b1ackcoffee  but hypothyroidism would decrease the height. +  

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1B2 ecoms mofr tonreip dan is a cnseesyra fcctaroo orf tnhoieiemn .ehnstysa Lwo 12B = lwo tie.hinnome

 -3  upvote downvote
submitted by mcl(501),
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nnoiheietM is an sltiseena imnao ia.dc All tosreh selidt are ot.n

scalpelofthenorth  Pg 81 Tyrosine is listed as an essential AA. Should be tryptophan for those who got this wrong like me. +  
neonem  But tyrosine can come from phenylalanine, so it's not really essential right? +  
gh889  in FA2019, it is listed as Tryptophan, not Tyrosine. That was corrected. +7  
usmleuser007  Note: Tyrosine is ONLY essential with PKU in children +  
niboonsh  bro FA2018 lists tyrosine as an essential AA. They played us. +1