Lac operon?

[turkeyjerky]

Advertisement - Members don't see this ad

Do we actually have to know this $hit? There're like 50 questions on it in Uworld, but I don't see it anywhere else and I couldn't give less of a f#ck whether the level of cAMP is high or low when lactose is present.

 

[mq123]

Do we actually have to know this $hit? There're like 50 questions on it in Uworld, but I don't see it anywhere else and I couldn't give less of a f#ck whether the level of cAMP is high or low when lactose is present.

I can never remember that stuff either -- every time I read, it 'comes back' to me and I understand it, but then I forget it the next day. That will be one of the things I cram the night before 👍

 

[StereoSanctity]

not sure... but HY Cell & Molc Bio has a whole chapter on it (granted, each chapter is like <5 small pages).

I have a vague idea of how it works, but its not going on my last-minute things to look over list.

I take this thing tomorrow, so I'll report back if I have any questions on it...

 

[badasshairday]

I think the whole hype on the lac operon was the fact that the NBME put it on Step 1 a few years ago, and people were like WTF? I think that is why UWORLD put it in, and part of the reason HY Cell and Molec has been so hyped up.

 

[PokerDoc]

One promotor encodes all the genes, active in absence of glucose only, otherwise repressed.. blah blah

thats all im gonna remember

 

[turkeyjerky]

the thing that gets me about is all the dumb names associated with it, like "operator", wtf does that mean? the overall concept is easy enough, but actually memorizing each of the steps is as tedious as the f'ing tca cycle.

okay, so maybe it's not exactly hard, but it just seem so pointless

 

[username456789]

the thing that gets me about is all the dumb names associated with it, like "operator", wtf does that mean? the overall concept is easy enough, but actually memorizing each of the steps is as tedious as the f'ing tca cycle.

okay, so maybe it's not exactly hard, but it just seem so pointless

I agree, molecular genetics or whatever this is even called has always confused the hell out of me. I get it down right before the exam, then drop it all. Regulators, promotors, operators, repressors, helpers, modifiers, cofacilitators, codependents, transcription factors, blah blah blah. It's all noise garbage to me.

It's the scientific equivalent of fancy flowery poetry.

 

[PokerDoc]

I agree, molecular genetics or whatever this is even called has always confused the hell out of me. I get it down right before the exam, then drop it all. Regulators, promotors, operators, repressors, helpers, modifiers, cofacilitators, codependents, transcription factors, blah blah blah. It's all noise garbage to me.

It's the scientific equivalent of fancy flowery poetry.

I only got this question right in UW b/c of sophomore year biochemistry in college... that says all you need to know right there lol..

 

[kissmyasthma99]

In DIT, he actually included a whole page on the Lac operon, and he said that he has reports of people being tested on it. If you know someone who is taking DIT, copy that page out of their handbook. It's only one page, and it does a good job explaining it. He used two images out of Microbiology of The Cell that explain it pretty well. It's really easy once you review it, so I would take a couple of minutes to sit down and review it. As soon as you don't, it will end up on your test, and you will be kicking yourself 🙂

 

[greg1184]

At least they haven't thrown the Trp Operon yet.

I think is funny how big of a fetish the scientists have for this topic, Polycistronic RNA. I had it in High School Biology, College Biology, and Medical School. Priceless.

 

[Bassix]

the thing that gets me about is all the dumb names associated with it, like "operator", wtf does that mean? the overall concept is easy enough, but actually memorizing each of the steps is as tedious as the f'ing tca cycle.

okay, so maybe it's not exactly hard, but it just seem so pointless

Man, I hear ya on that. The unfortunate part about medicine is that it's convoluted with so many extraneous words. I guess those bench scientists and young gung-ho med students need to get their egos inflated somehow. 😀

 

[TexasTriathlete]

I was bitching about this yesterday. I had that idiotic thing memorized inside and out for the MCAT, but now I don't remember it at all.

 

[Domenech]

Just spend 10-15 minutes studying it from Kaplan Biochemistry textbook. Not a very difficult concept. There's a question somewhere in nbme on it. So if it's on nbme, you can very well expect it on usmle step 1 as well.

Oh plus the fact that thing landed a nobel prize for three French scientists in 1965.....Now you know you gotta do it 👍

 

[RapidReview]

In DIT, he actually included a whole page on the Lac operon, and he said that he has reports of people being tested on it. If you know someone who is taking DIT, copy that page out of their handbook. It's only one page, and it does a good job explaining it. He used two images out of Microbiology of The Cell that explain it pretty well. It's really easy once you review it, so I would take a couple of minutes to sit down and review it. As soon as you don't, it will end up on your test, and you will be kicking yourself 🙂

just covered it today in DIT. he gets feedback from recent test takers, and he prides his program only on HY material, so if he chooses to put it in his HY material, i would spend a few minutes looking over it. honestly, a 15 minute overlook would be sufficient, esp since we've all seen it many times over the past 6ish years.

 

[dienekes88]

I drew it out on a Postit and stuck it to my wall.

Lac I, Promoter, Operator, LacZ, LacY, LacA

A couple arrows, some symbols... that's about all I'll do.

Ha. Some of us haven't seen it many times.

 

[username456789]

I drew it out on a Postit and stuck it to my wall.

Lac I, Promoter, Operator, LacZ, LacY, LacA

A couple arrows, some symbols... that's about all I'll do.

Ha. Some of us haven't seen it many times.

Seriously. I saw it once in college as a freshman nearly 10 years ago, definitely didn't study it for the MCAT, and saw it once in med school last year. And then a few days ago in UW.

 

[Salpingo]

This has become a big pet peeve of mine, right up there with the vast majority of embryology. Can't wait to be done with it.

DIT explains it well: for transcription of Lac gene, you need CAP on and the repressor off. Logically, if there's glucose present or lactose absent, you don't want the gene on. So if you can remember glucose interacts with CAP (bonus points for remembering the cAMP connection), and lactose is responsible for the repressor (bonus points for remembering the allolactose connection), you can sort of figure it out. Glucose gets rid of CAP, because that would prevent gene transcription, and lactose gets rid of the repressor, because that's keeping transcription from happening.

After that, you need to remember that the repressor is on the operator. So those are the three facts I'm going to memorize on the 25% chance that there's a question affecting 1% of my overall score.

 

[HTxFrog]

I had it on an NBME or a shelf or something one time and I was like WTF, lac operon, do I remember this from my freshman bio class?? well yeah, I didn't remember it. stupid ass question

 

[usmletoo]

only 6 - promise - you might get one or two in the real thing...your call -

😍

 

[TexasTriathlete]

I just talked to one of my classmates, who took the exam on Monday, and he told me he got a Lac operon question. Just FYI.

 

[turkeyjerky]

I just talked to one of my classmates, who took the exam on Monday, and he told me he got a Lac operon question. Just FYI.

muthaf-cker

 

[1nycdoc8]

This has become a big pet peeve of mine, right up there with the vast majority of embryology. Can't wait to be done with it.

DIT explains it well: for transcription of Lac gene, you need CAP on and the repressor off. Logically, if there's glucose present or lactose absent, you don't want the gene on. So if you can remember glucose interacts with CAP (bonus points for remembering the cAMP connection), and lactose is responsible for the repressor (bonus points for remembering the allolactose connection), you can sort of figure it out. Glucose gets rid of CAP, because that would prevent gene transcription, and lactose gets rid of the repressor, because that's keeping transcription from happening.

After that, you need to remember that the repressor is on the operator. So those are the three facts I'm going to memorize on the 25% chance that there's a question affecting 1% of my overall score.

Nice, just to add on:

CAP is also known as the INDUCER if that makes things easier (in that at the very least you need the inducer present to turn on the operon. However if the inducer and the repressor are both present (when you have no glucose or lactose present) the operon is still off.

CAP is bound to the DNA only when there is high cAMP. You only have high cAMP when glucose is ABSENT (inverse relationship with glucose and cAMP levels).

Anyways, screw the lac operon 👎

 

[PokerDoc]

ok I got it down good now (btw, i have DIT's sham course to thank for it)


basically in bullet format:

Only need to remember CAP and Repressor

CAP: only present when glucose is NOT present
Repressor: only present when lactose is NOT present

thus, the only scenario where the lac operon works is when CAP is present (no glucose) and the repressor is off (lactose is present)


there

done