High Yield Question #13 - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
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


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 04-09-2011
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 487
Threads: 95
Thanked 1,459 Times in 357 Posts
Reputation: 1469
Arrow High Yield Question #13

Which of the following is the function of the large subunit of the ribosome?

A) Bind messenger RNA (mRNA)
B) Bind transfer RNA (tRNA)
C) Catalyze peptide bond formation
D) Link adjacent ribosomes in a polyribosome
E) Initiate protein synthesis
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (04-10-2011)



  #2  
Old 04-09-2011
USMLE Forums Guru
 
Steps History: 1 + CS
Posts: 405
Threads: 55
Thanked 528 Times in 155 Posts
Reputation: 538
Smile

A) Bind messenger RNA (mRNA) - Massive RNA

t-RNA - tiny RNA

r-RNA - rampant RNA (From FA 2010).
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-09-2011)
  #3  
Old 04-09-2011
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 590
Threads: 31
Thanked 1,230 Times in 411 Posts
Reputation: 1254
Default

I would have chosen C.

I think A and B are the smaller subunit; I don't even know what D is, and E sounds a lot like A...
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-09-2011)
 
  #4  
Old 04-09-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 298
Threads: 45
Thanked 718 Times in 210 Posts
Reputation: 728
Default

ahhh biochem!

I would guess B. haven't studied this in a while but I seem to recall that tRNA binds to the larger subunit

But C sounds promising too.

Good question.
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-09-2011)
  #5  
Old 04-09-2011
USMLE Forums Newbie
 
Steps History: ---
Posts: 3
Threads: 0
Thanked 4 Times in 2 Posts
Reputation: 14
Default

I will go with B.

There are antibiotics that block tRNA from attaching to the 50S subunit of bacteria.
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-09-2011)
  #6  
Old 04-09-2011
USMLE Forums Scout
 
Steps History: 1 + CK
Posts: 91
Threads: 17
Thanked 108 Times in 37 Posts
Reputation: 118
Default

Quote:
Originally Posted by aktorque View Post
Which of the following is the function of the large subunit of the ribosome?

A) Bind messenger RNA (mRNA)
B) Bind transfer RNA (tRNA)
C) Catalyze peptide bond formation
D) Link adjacent ribosomes in a polyribosome
E) Initiate protein synthesis
I'll go for C
A: bind messenger RNA: 40 s
b/ Bind transfert RNA, 40S ( 60 S bound aminoacyl-tRNA instead)
D:??
E: initiate protein synthesis/40S


small subunit bound to the mRNA then an initiator tRNA is attracted to the region (code for methionine)
then the large ribosomal subunit will bind to the small subunit, it has A site and a P site. which are different binding sites for the tRNAs.
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-09-2011)
  #7  
Old 04-09-2011
USMLE Forums Scout
 
Steps History: Not yet
Posts: 59
Threads: 15
Thanked 30 Times in 19 Posts
Reputation: 40
Default

I think its B.
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-09-2011)
  #8  
Old 04-09-2011
USMLE Forums Addict
 
Steps History: 1 + CS
Posts: 103
Threads: 29
Thanked 18 Times in 13 Posts
Reputation: 28
Default

i would go with B ....correct answer plzz
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-09-2011)
  #9  
Old 04-09-2011
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 487
Threads: 95
Thanked 1,459 Times in 357 Posts
Reputation: 1469
Correct Answer

Quote:
Originally Posted by tinhi View Post
I'll go for C
A: bind messenger RNA: 40 s
b/ Bind transfert RNA, 40S ( 60 S bound aminoacyl-tRNA instead)
D:??
E: initiate protein synthesis/40S


small subunit bound to the mRNA then an initiator tRNA is attracted to the region (code for methionine)
then the large ribosomal subunit will bind to the small subunit, it has A site and a P site. which are different binding sites for the tRNAs.

Quote:
Originally Posted by Mondoshawan View Post
I would have chosen C.

I think A and B are the smaller subunit; I don't even know what D is, and E sounds a lot like A...

Wow, well done guys. I'm very impressed. One more time you guys have proved your intelligence.

Correct ans is C) Catalyze peptide bond formation

The large subunit of the ribosome catalyzes peptide bond formation by activation of peptidyl transferase. The small ribosomal subunit contains the peptidyl-tRNA-binding (P) site that binds the tRNA molecule attached to the carboxyl end of the growing end of the polypeptide chain.

The small subunit also contains the aminoacyl-tRNA-binding (A) site that holds the incoming tRNA and amino acid. The initiation factors are loaded on the small ribosomal subunit that must locate the AUG (start) codon to initiate protein synthesis. This occurs before binding of the large subunit. In addition, the initiator tRNA containing methionine provides the amino acid necessary to start protein synthesis.

The initiator tRNA is also located on the small subunit. It resides at the P site (the normal peptidyl site) even though it is an aminoacyl-tRNA. This occurs before binding to the mRNA. Therefore, the initiation phase of protein synthesis is regulated by the small subunit of the ribosome. Ribosomes are composed of both protein and RNA (predominately rRNA, but also mRNA and tRNA).

Single ribosomes are involved in synthesis of cystolic proteins. Polyribosomes (linked by mRNA) synthesize proteins that are translocated into the cisternal space of the rough endoplasmic reticulum (RER) and destined for export or specific organelles.
Reply With Quote Quick reply to this message
The above post was thanked by:
Abdulaziz (04-10-2011), apx85 (04-09-2011), donofitaly (04-09-2011), Mondoshawan (04-09-2011), spasemaster (02-15-2015)
  #10  
Old 04-09-2011
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 487
Threads: 95
Thanked 1,459 Times in 357 Posts
Reputation: 1469
Arrow

Practice qns

http://www.megaupload.com/?d=DSIHJ537
Reply With Quote Quick reply to this message
  #11  
Old 04-09-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 298
Threads: 45
Thanked 718 Times in 210 Posts
Reputation: 728
Default

Tetracycline's block tRNA binding to 30s subunit. Don't think I'll forget that now. Thanks!

Good question
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (04-10-2011), rseruy (12-09-2012)



Reply

Tags
Molecular-Biology-, Step-1-Questions

Quick Reply
Message:
Options

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:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
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.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

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
High Yield Question #9 aktorque USMLE Step 1 Forum 8 07-26-2011 12:01 PM
High Yield Question #6 aktorque USMLE Step 1 Forum 23 04-13-2011 07:40 PM
High Yield Question #10 aktorque USMLE Step 1 Forum 9 04-07-2011 10:53 AM
High Yield Question #5 aktorque USMLE Step 1 Forum 10 04-03-2011 10:32 AM
High Yield Question #4 aktorque USMLE Step 1 Forum 5 04-02-2011 05:12 PM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 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)