nbme 5 block 3 q 32 - sara84

[ArchivalUser]

Ribosomes are reconstituted from 30S and 50S subunits purified from streptomycin-sensitive (S) and streptomycin-resistant ® Escherichia coli. These ribosomes are then added to a phenylalanine incorporation system. Incubations are carried out with or without streptomycin, and the amount of radioactive phenylalanine incorporation is measured (results shown in the table).



Proteins from -----Proteins from---------- -Incorporation Activity (cpm x 100)

30S Subunit -------50S Subunit --------------- -without --------------------------with

S12-- S5------------- S16-- S14------------------ Streptomycin---------------- Streptomycin

S----- S--------------- S------ S------------------- 63----------------------------- 41

R----- S--------------- S------ S------------------- 62----------------------------- 61

S----- R--------------- S------ S------------------- 59----------------------------- 31

R------ R--------------- S----- S------------------- 42----------------------------- 40

S------ S--------------- R----- S------------------- 42----------------------------- 27

S--- ----S-------------- S----- R------------------- 61----------------------------- 40

S------- S-------------- R----- R------------------- 59----------------------------- 37

The action of streptomycin is most likely mediated by an interaction with which of the following proteins?

a) S5 protein

b) S12 protein

c) S14 protein

d) S16 protein


Why is n't the answer D???

Streptomycin is a protein synthesis inhibitor. It binds to the small 16S rRNA of the 30S subunit of the bacterial ribosome, interfering with the binding of formyl-methionyl-tRNA to the 30S subunit.


30 S RNA HAS JST ONE SUBUNIT WHIC IS 16 SRNA

[ArchivalUser]

Anyone???????????

[ArchivalUser]

streptomycine is an aminoglycoside....so it effects on 30S subunite
NBME explanation is pretty clear and I recommend to reread it.

[ArchivalUser]

Streptomycin is a protein synthesis inhibitor. It binds to the small 16S rRNA

[ArchivalUser]

The question is not about the pharmacological effects of streptomycin. You have to use the date given in the question. According to the data in the table, streptomycin can't exert its effect when S12 is resistant and all the other subunits are susceptible (row 2). Row 4 also supports this. The other rows have other subunits resistant, but streptomycin is still able block protein synthesis. So, based on all this information, the answer should be S12 (choice B).

[ArchivalUser]

Although I really don't understand the question but one of my teacher said the answer is B.He also think as fuzuli using data given.

[ArchivalUser]

If you look at every row that has only one R, you can see whether or not streptomycin was able to exert its effect (decrease activity).. the rows with more than one R are useless bc confounding.
The only row with one R that shows a decrease in activity is row 2... so when the S12 protein is changed/resistant, streptomycin can't interact with it and exert its effect.
Hope this helps!