E. coli in absence of Glucose and Lactose - USMLE Forums
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  #1  
Old 04-30-2012
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Bacteria E. coli in absence of Glucose and Lactose

How would lac operon in E. coli would be controlled in the absence of both glucose and lactose?

A) CAP bound to operator&repressor bound to CAP site-> infrequent transcription
B) CAP site empty&repressor bound to operator-> infrequent transcription
C) CAP bound to CAP site&repressor bound to operator-> infrequent transcription
D) CAP bound to CAP site&repressor removed-> frequent transcription

Special thanks to DocSikorski who inspired me with his question: E. coli Lactose Metabolism to dig deeper in my understanding of this

Last edited by Casandra; 04-30-2012 at 11:21 PM. Reason: a typo
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Old 05-01-2012
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Will go with D , though I need to revise this again 😥😖


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Old 05-01-2012
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@Kabutar111 - If you read DocSikorski's question I mentioned and all comments below it you don't need to revise more - it's all there
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Quote:
Originally Posted by Casandra View Post
@Kabutar111 - If you read DocSikorski's question I mentioned and all comments below it you don't need to revise more - it's all there
What is this CAP site ???

Or my just totally lost here
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Old 05-01-2012
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Quote:
Originally Posted by Kabutar111 View Post
What is this CAP site ???

Or my just totally lost here
Check the video here

Lac operon
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Old 05-01-2012
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C)...............
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Old 05-01-2012
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Default correct answer is...

C) CAP bound to CAP site & repressor bound to operator-> infrequent transcription

1st rule that I put into my head was that E.coli is a good energy saver - it doesn't synthesize the enzyme that it doesn't need. So e.g. if there's no lactose -> it won't synthesize the lactase.

1st step - since the stem said that there's no glucose nor lactose I would exclude answer saying that there will be frequent transcription.

2nd - When glucose is absent - cAMP increases (that's what I've learned today ) and binds to CAP and activates it. Next, CAP binds to CAP site.

@Kabutar111 - All is nicely explained and visualized here: http://highered.mcgraw-hill.com/olcw...20Lac%20Operon
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Old 05-14-2012
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C...just did this on dit
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Old 05-17-2012
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Quote:
Originally Posted by Casandra View Post
C) CAP bound to CAP site & repressor bound to operator-> infrequent transcription

1st rule that I put into my head was that E.coli is a good energy saver - it doesn't synthesize the enzyme that it doesn't need. So e.g. if there's no lactose -> it won't synthesize the lactase.

1st step - since the stem said that there's no glucose nor lactose I would exclude answer saying that there will be frequent transcription.

2nd - When glucose is absent - cAMP increases (that's what I've learned today ) and binds to CAP and activates it. Next, CAP binds to CAP site.

@Kabutar111 - All is nicely explained and visualized here: http://highered.mcgraw-hill.com/olcw...20Lac%20Operon

Wow... took me like 1~ hr to get this topic but now it's mine... crystal clear

Thank you Casandra


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Old 05-17-2012
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Quote:
Originally Posted by Dr. Mexito View Post
Wow... took me like 1~ hr to get this topic but now it's mine... crystal clear

Thank you Casandra

P.S.
I really like your name... Can you really see the future?
I'm really glad it helped So many questions posted on this website help me in grasping and integrating some ideas, that I can't think of a better way of doing this!

about the future... I foresee me and the Step 1 books spending lots of time together in the next few months
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