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Old 08-16-2011
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Question streptomycin resistance

Ribosomes are reconstituted from 30S and 50S subunits purified from streptomycin-sensitive (S) and streptomycin-resistant (R) 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
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Old 08-16-2011
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Can you pls state the source of this quesiton? thanks
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Old 08-16-2011
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The change in incorporation activity is highest(28) when the S5 resistence is there so I will go with A... I hope it's just a simple math as I thought
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Old 08-16-2011
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Send a message via Yahoo to ricko335

wow i am absolutely clueless but i read somewhere about ribosomal s12 protein in resistance
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Old 08-16-2011
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It is S12
as in the second line with S5 sensitive there is no change
but in line three with S12 sensitive there is a big change
also when S5o ribosome was sensitive both subunits and S30 ribosome subunits resistant in line 4 no change

so the effect is mediated by S30 ribosome especially S12 subunit
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Old 08-23-2011
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this is NMBE 5 question
To incorporate the phenylalanine ( which is an amino acid) you need an intact Ribosomal structure (both subunits are working), now, streptomycin interacts with one of the proteins that constitutes the big or small unit of the ribosome ( you can cheat by already knowing that Aminoglycosides affect the S30 subunit, but we wont even need that, since the question gives us all the answers)

Now when ALL parts of the ribosome are SENSITIVE to Strep. Obviously, the incorporation would occur in a higher percentage when there is no strep. , so what we will do, is to look at when each subunits is resistant, when does the incorp. decreases ? you can see from the question the when proteins from S30 are both R & R, then the incorp. is decreasing, no matter what the status of S50 components is. this tells us that the little protein that strep. messes up, is inside S30. Now next move, we look to S30 and check when we have Sensitive Piece and a resistant piece : when does the incorp. decrease in this case ? it decreases when the S12 is Resistant ... Thus the protein affected is S12
nothing is impossible!
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