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NBME 21 Answers

nbme21/Block 1/Question#17
A 7-year-old girl is brought to a clinic in a ...
Methionine🔍

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 +14  upvote downvote
submitted by usmleuser007(273),

If you couldn't remember which were essential; then alternative would have been to realize that growing children need cells to divide. This requires DNA replication and translation. Of which the nucleic acid thyime is important. It requires a methyl transfer.

This is where methionine comes in. Methionine combines with ATP to form SAM (a methyl donor)

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 :) +  



 +12  upvote downvote
submitted by nosancuck(62),

Yo dawg we all about PVT TIM HaLL

Phenylalanine, Valine, TryptoDANK, Threonine, Isoleucine, Methionine, Histidine, Leucine Lysine

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 https://www.sciencedirect.com/science/article/pii/S0955286304000701?via%3Dihub +  



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
pparalpha  Thanks! Good mnemonic +1  
b1ackcoffee  best mnemonic +  



essential Amino acids (AA)

1) Adults require 9 (AA) = able to make argnine via urea cycle 2) Children require 10 (AA) = they are still developing 3) With PKU tyrosine becomes essential in both adults and children




 +0  upvote downvote
submitted by hello(180),

For anyone confused trying to follow @usmleuser007's comment

Slightly modified

Essential amino acids mnemonic "Ah, Three fans will try meth"the

Ah = arginine, histidine

Three = Threonine

Fans (phans)= Phenylalanine

Vill (will -- German accent pronouncing English word "will") = valine, isoleucine, leucine, lysine

Try = tryptophan

Meth = Methionine




 +0  upvote downvote
submitted by mrglass(13),

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 drzed(87),

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 saqeer(0),

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. +  



1-letter-abbreviation-accurate mnemonic for essential amino acids:

"MLK eradicated HIV FTW"

M = Methionine

L = Leucine

K = Lysine

H = Histidine

I = Isoleucine

V = Valine

F = Phenylalanine

T = Threonine

W = Tryptophan

P.S. It's MLK Day in the U.S. so perfect time to learn about Martin Luther King Jr.'s biochemistry/infectious disease side hustle.




B12 comes from protein and is a necessary cofactor for methionine synthase. Low B12 = low methionine.




 -3  upvote downvote
submitted by mcl(447),

Methionine is an essential amino acid. All others listed are not.

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. +1  
usmleuser007  Note: Tyrosine is ONLY essential with PKU in children +  
niboonsh  bro FA2018 lists tyrosine as an essential AA. They played us. +1  



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