need help with your account or subscription? click here to email us (or see the contact page)
join telegramNEW! discord
jump to exam page:
search for anything ⋅ score predictor (โ€œpredict me!โ€)

NBME 20 Answers

nbme20/Block 1/Question#34 (reveal difficulty score)
A strain of Escherichia coli produces a ...
Missense ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: biochem

 Login (or register) to see more

 +29  upvote downvote
submitted by โˆ—hayayah(1212)
get full access to all contentpick a username

Missense mutations involve a nucleotide substitution resulting in changed amino acids. Sometimes the effects of missense mutations may be only apparent under certain environmental conditions; such missense mutations are called conditional mutations. Many missense mutations result in proteins that are still functional, at least to some degree.

Also, all the other answers would probably leave you with either a greatly altered or non-functional protein.

get full access to all contentpick a username
thefoggymist  I chose nonsense because I thought it'll make the enzyme shorter (since less bonds = more heat liable = can't work at 42 degrees) but yea, probably won't work even at 30 if it's an early nonsense. +11
joanmadd  A good clinically related example is HbC disease on electrophoresis. HbC disease is due to a missense mutation (glutamic acid (-) for valine (neutral)). The mutated hemoglobin is still fairly functional but when placed on gel electrophoresis the HbC migrates the least far from the negative electrode due to less negative propulsion (lack of wild type glutamic acid). +3
fatboyslim  @Joanmadd Just to clarify, glutamic acid substitution for valine occurs in sickle cell disease not HbC. HbC is glutamic acid substitution for lysine :) +8
rockodude  lyCCCCine for HbC +4
l0ud_minority  I was thinking this was r/t a transposon inserting itself in DNA. +1

 +0  upvote downvote
submitted by andremosq(9)
get full access to all contentpick a username

Missense - Nucleotide substitution results in CHANGED what happens on Sickle cell disease, substitution of glutamic acid with valine..

the question says requires exogenous tryptophan for growth at 42 but no at 30.. so its still partially functional,so it cant be NONSENSE.

get full access to all contentpick a username

Must-See Comments from nbme20

amorah on Cytomegalovirus infection
masonkingcobra on Contact with parakeets
hayayah on Capillary hydrostatic: increased; ...
hayayah on X chromosome-linked isoenzymes
medbitch94 on Mannose 6-phosphate
hello on Capillary hydrostatic: increased; ...
hayayah on Osteoblasts
imgdoc on Hypophosphatemia
hayayah on Missense
celeste on 50%
justgettinby on Omeprazole
andrewk1 on Cold, dry air
yotsubato on Jugular venous pressure of 12 mm Hg
strugglebus on Drug effect

search for anything NEW!