streptomycin resistance - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
USMLE Articles
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam

Thread Tools Search this Thread Display Modes
Old 08-16-2011
laurier's Avatar
USMLE Forums Addict
Steps History: CK Only
Posts: 106
Threads: 19
Thanked 69 Times in 32 Posts
Reputation: 79
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
Reply With Quote Quick reply to this message
The above post was thanked by:

Old 08-16-2011
USMLE Forums Guru
Steps History: ---
Posts: 337
Threads: 48
Thanked 162 Times in 105 Posts

Can you pls state the source of this quesiton? thanks
Reply With Quote Quick reply to this message
Old 08-16-2011
drnrpatel's Avatar
Steps History: 1+CK+CS
Posts: 441
Threads: 153
Thanked 393 Times in 211 Posts
Reputation: 416

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
Reply With Quote Quick reply to this message
Old 08-16-2011
USMLE Forums Master
Steps History: Not yet
Posts: 674
Threads: 264
Thanked 958 Times in 393 Posts
Reputation: 968
Send a message via Yahoo to ricko335

wow i am absolutely clueless but i read somewhere about ribosomal s12 protein in resistance
Reply With Quote Quick reply to this message
Old 08-16-2011
USMLE Forums Veteran
Steps History: Not yet
Posts: 259
Threads: 118
Thanked 291 Times in 115 Posts
Reputation: 301

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
Reply With Quote Quick reply to this message
Old 08-23-2011
dr_lizard's Avatar
USMLE Forums Addict
Steps History: Not yet
Posts: 192
Threads: 17
Thanked 95 Times in 58 Posts
Reputation: 105

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!
Reply With Quote Quick reply to this message


Microbiology-, Pharmacology-, Step-1-Questions

Quick Reply

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Where you live. Leave blank if you don't want to tell.


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
Bacterial Drug Resistance achistikbenny USMLE Step 1 Forum 7 09-21-2013 01:47 AM
Mechanism of resistance to chemotherapy kemoo USMLE Step 1 Forum 4 10-01-2012 11:30 PM
The concept of Insulin Resistance jattdoc USMLE Step 1 Forum 2 06-29-2011 03:35 PM
malaria resistance in blood disorders Rawalian USMLE Step 1 Forum 1 04-28-2011 03:18 PM
Drug resistance? dheshah USMLE Step 1 Forum 1 09-07-2010 10:37 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)