Talk:Lac operon

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Untitled
More info needed in this article. There seems to be more info on lac operon scattered around than here... Delta G 05:40, 4 Apr 2004 (UTC)

Historical part
I think that a short historical part could be of some importance. Explain why people were interested in this operon, what were the fondamental questions tackled (how genes are regulated)? And maybe also a reference to the people who first discovered the mechanism of regulation of this operon (at least a part of it), and a reference to their nobel prize (Jacob, Lwoff, Monod; physiology 1965). —Preceding unsigned comment added by 193.54.85.217 (talk) 14:15, 9 December 2009 (UTC)

Information added...
I did my research project on the lac operon a couple years ago, so I've gone ahead and boldly added a paragraph on the purpose of the lac operon, and added a description of the role of the Catabolite Activator Protein and cAMP after the description of the repressor, since the picture referenced illustrated role of the CAP/cAMP, but there was no mention of it. I may have made some of the "role of cAMP" section redundant, but I think it is necessary to explain CAP/cAMP in the main section, not just an afterthought. The Human Spellchecker (talk) 20:33, 1 October 2008 (UTC)

Just a comment about this article being too techincal
IT's NOT! I have taken a quarter of HIGH SCHOOL biology and understand this article completely. By the way, I moved the text that was below the diagram up so that people could better understand the diagram, as I made the mistake of trying to understand the diagram without reading the text below. MAJOR mistake, took me two hours to fifure it out. And yes, I do go to the Illinois Mathematics and Science Academy, one of the most prestigious high schools in the nation.

Do you want a cookie? —Preceding unsigned comment added by 128.227.195.92 (talk) 19:54, 27 March 2008 (UTC)

Someone should add the roll allolactose plays in the workings of the lac operon. DavidMendoza
Done. --Memenen 13:27, 1 October 2005 (UTC)

What is the relation between lac operon and lac repressor
Does it mean that lac repressor is the protein transcribed from lac operon? --22:03, 3 Dec 2004 61.171.37.146 By Dr. SYED FARHATULLAH:The lac repressor is expressed from a gene, lacI, not within the lac operon. The lac operon produces one polycistronic mRNA which codes from three different proteins: lacZ, lacY, and lacA. LacZ is β-galactosidase which cleaves lactose, lacY is lactose permease which is a membrane protein to allow lactose to enter the cell, and lacA is transacetylase which has unknown purpose. The lac repressor is produced outside of the lac operon and binds to the operator in the lac operon, just upstream of the coding genes and downstream of the RNA polymerase binding site/promoter. Hope this helps. --G3pro 03:31, 4 Dec 2004 (UTC)

lac operon
The title of this article is incorrect. It should be lac operon. Let's remember correct convention. By using Lac operon the implication is that we are talking about a protein. Does anyone know how to change the way the title of the article looks? There were many instances of Lac being used to describe DNA or mRNA, try to use correct convention, lacI is the repressor gene or cistron, LacI is the repressor protein, this is one of the most basic rules of genetics/molecular biology.--Alun 17:53, 13 May 2005 (UTC)

major edit contemplated
I'd like to make a contribution to this article but am not sure of protocol. Following is my suggested text for introductory paragraphs. I have other changes to the rest of the text.

The lac operon consists of three closely linked genes required for the transport and metabolism of lactose (milk sugar) in the bacterium Escherichia coli (E. coli) and some other enteric bacteria. Control of the lac genes was the very first genetic regulatory mechanism to be understood---one reason is that it is the simplest, at least in basic outline.

The genes of the lac operon include two important ones: lacZ encodes an intracellular enzyme (LacZ, beta-galactosidase), that cleaves the disaccharide lactose into glucose and galactose. A second gene, lacY, encodes a transport protein (LacY, lactose permease) that pumps lactose into the cell. Specific control of the lac genes depends on the presence of the substrate lactose in the growth medium. The genes are highly transcribed into messenger RNA (mRNA), and the mRNA then translated into protein, only when lactose is present.

The lac genes are organized into an operon---they are oriented in the same direction immediately adjacent on the chromosome and are co-transcribed into a single mRNA molecule. Transcription of all genes starts with the binding of the enzyme RNA polymerase (RNAP) to a specific binding site on the DNA next to the gene called the promoter. The lac promoter is just upstream of the lacZ gene, from which position RNAP proceeds to copy all three genes (lacZYA) into mRNA.

The regulatory response to lactose requires an intracellular regulatory protein called the lactose repressor. If lactose is missing from the growth medium, the repressor binds very tightly to a short DNA sequence just downstream of the promoter near the beginning of lacZ called the lac operator. Repressor bound to the operator interferes with binding of RNAP to the promoter, and therefore mRNA encoding LacZ and LacY is only made at very low levels. When cells are grown in the presence of lactose, a lactose metabolite called allo-lactose binds to the repressor, causing a change in its shape. Thus altered, the repressor is unable to bind to the operator, allowing RNAP to transcribe the lac genes and thereby leading to high levels of the encoded proteins.

For their work in elucidating lac regulation, Jacques Monod and Francois Jacob, working at the Pasteur Institute in Paris, received the Nobel Prize in Physiology or Medicine in 1965. In addition to the first discovery of a genetic regulator (the repressor) and its site of action on DNA (the operator), other fundamental insights from their work include (i) the discovery of co-regulation of the lac genes; (ii) the invention of genetic tools both for selecting and classifying mutants defective in either repressor or operator;  (iii) the distinction between negative and positive regulation;  and (iv) the discovery of lactose analogs that are substrates for beta-galactosidase but not inducers and others which are inducers but not substrates. The last point was critical in separation of prior speculations from modern models of genetic control. telliott


 * There's no protocol, anyone can edit anything. If there are any disagreements then they should be discussed on the talk page. If someone doesn't like what you've done they will change it or leave a message there. I think this article could be a lot better, it probably needs someone who is prepared to devote some quality time to it. I did a bit of editing a few months ago, italicised E. coli and lac, also rewrote the regulation section. If you have the time and inclination then go for it. Best of luckAlun 12:14, 30 September 2005 (UTC)
 * p.s. I would like to change the title to lac operon (from Lac operon, which is wrong), but I don't want to do this if article titles can't be italicised, because it would just be lac operon then, and I didn't want to move the article to this title if it was irreversible. Do you think it's worth it?Alun 12:21, 30 September 2005 (UTC)
 * I inserted the template that was made for the purpose of dealing with article titles that should not start with an upper case letter. --Memenen 13:31, 1 October 2005 (UTC)
 * Nice one.Alun 15:16, 1 October 2005 (UTC)

Major Edit Carried Out
I've merged in Tom Elliott's content above, as well as merging redundant sections of the article, and partitioning them into subsections. I still need to write a bit about IPTG, I may have missed italicizing a few gene names, and the Discovery section probably needs a little work, still. This article was a complete mess, though: it looks like content was just dumped in without reading the rest of the article. -Kieran 13:43, 3 October 2005 (UTC)

Allolactose merger
What's the point of the allolactose article? Put it's pathetic content here and merge I say!!!!Alun 12:31, 30 September 2005 (UTC)
 * I suggest that the allolactose article be left as it is. If it is deleted, someone else will just make it again. It hurts nothing. --Memenen 13:31, 1 October 2005 (UTC)
 * They won't be able to, because a search for allolactose will be redirected here. The article page will still exist (as a redirect) so anyone trying to re-create it will just get a message saying that the page title already exists. For example, try going to USA, you will end up at United StatesAlun 14:59, 1 October 2005 (UTC)

Go ahead and merge them-it provides context, and the redirect could be to that specific section of the lac operon article. Its not like there needs to be a separate entry for every single idea. Allow readers to see why allolactose is important.
 * I have created these two images using Chemtool 1.6 a free downloadable chemical structure drawing package (there's a few available).






 * So which would be the better to use? Personally I'm favouring the second at the moment, but I'm open to persuasion.
 * I think that it's best not to add an additional allolactose section stating that the above Regulation by lactose section is simplified. It is better to edit the regulation by lactose section and change it to Regulation by allolactose. I have done this, but it's from memory so please if I've remembered wrongly then correct my mistakes, I haven't looked at any of this stuff seriously since I left Uni in '94. I've changed the allolactose section to an IPTG section.
 * I've also redirected allolactose here. If anyone's not happy with this then please make it better. Cheers.Alun 17:42, 2 October 2005 (UTC)
 * I like the second figure. And even though it's not acccurate, I prefer the old-fashioned views where the bonds go straight up and down from the sugar rings.  Also, the 1 position of glucose should be the same in both allolactose and lactose (I think it's beta).Telliott 16:08, 4 October 2005 (UTC)
 * Is the structure wrong? I had a look and they do seem to be different, have I got the glucose and galactose in different positions in the two diagrams? I was never very good at picturing these things in 3D. Are both sugars glucose in the Lactose for the second picture?Alun 17:00, 4 October 2005 (UTC)


 * The two diagrams are different, the chair diagram (top) is lacking a hydroxyl group on C4 of the first sugar. In addition, the anomeric configuration between the two sugars in the chair and harworth for lactose is different. Xcomradex 23:17, 19 June 2006 (UTC)

lac repressor merger
As we're on the subject of merging articles, is there any real point in having a seperate article for lac repressor? Surelly any information there should and could be merged here, and lac repressor redirected here. What's the general opinion?Alun 05:05, 3 October 2005 (UTC)
 * I disagree: The lac repressor article describes the protein itself, and takes more of a biochemical angle on its functioning. The lac operon article describes a coarser level of detail, more typical of the field of genetics (and is getting pretty bloated as it is). That's not to say that the lac repressor article doesn't need quite a lot of work, just that I think it contains information that belongs outside the article on the operon as a whole. If I get time, I'll put some work into filling out the repressor article. -Kieran 13:58, 3 October 2005 (UTC)


 * OK, I've expanded the repressor article, now. It might need some copyediting, but there's a lot of new information in there, that doesn't really belong in this one, but is related to it. -Kieran 16:07, 3 October 2005 (UTC)


 * I'm not sure I agree that the lac operon article is bloated, look at DNA or genetic code. But I take your point about genetics. It also occured to me that the lacI gene isn't actually part of the operon, so in retrospect maybe this isn't really the place for it.Alun 16:40, 3 October 2005 (UTC)

a different major edit
I just posted a complete rewrite. I should have checked this page first and would have seen your discussion. But I think the article needed a different structure and would rather proceed forward from this version. I hope you all think it's better. Obviously, if you thought it was bloated before, it's getting worse. But I think this article on lac is exactly the place to talk about basic elements of bacterial genetics. The section on glucose regulation is choppy and I will work on it. In particular it would be nice to explain why E. coli uses glucose in preference to lactose, when lactose contains glucose (and galactose is easily converted to glucose).Telliott 18:03, 3 October 2005 (UTC)


 * There is nothing wrong with this rewrite per se, but it could be considered over technical. This is an encyclopedia, not a text book, many of the technical phrases here are not explained. The article may be overly complicated and there may be too much detail. Even things like minimal medium will mean nothing to a reader who is not a biologist. I don't think that explanations of experimental work really belong in encyclopedias, but this is just my opinion. I think that it is extremely difficult to write these sort of articles for people who know nothing about science. Nevertheless, because this is an encyclopedia it is necessary to keep things as clear as possible to the uninitiated. I suggest you ask a friend or relative who has no biological training to read the article and to give you feedback, you might find that a great deal of it is meaningless to them. It is also important to include internal wiki links for words and terms which might need further explanation. I have already added a lot to the introduction and the first part of the article, but many more still need to be added. I have made some relatively minor alterations to phrases and words, little more than proof reading edits. I have also been playing around with chemical drawing packages and have included the structures of some of the lactose/allolactose analogues used in molecular biology. I might have a go at a major edit of this article in the near future, though I think it is fundamentally sound, it could possibly do with some major tinkering. On the whole I do like what you have done to the article, it is far more comprehensive than it was before.Alun 07:31, 16 October 2005 (UTC)
 * I have added a too technical tag.Alun 07:36, 16 October 2005 (UTC)
 * I think there are two different issues here. The first is whether the article is too complex.  I think it is an admirable, though impossible, goal for this encyclopedia to have as much information as possible.  The problem is to structure articles so that each progresses from less to more complicated, providing the reader with enough text (or links) so that they can educate themselves to the point of being able to understand the next section.  For the moment, coverage of most topics that I know something about is so sparse that I'm not tempted to add much more to this one.  But there is a second issue, rooted in the nature of science.  Science is not just facts.  It is the intellectual context---questions and ideas for solutions---that makes science alive.  The most interesting thing Jacob & Monod did was to distinguish between regulatory substances and their sites of action.  You can tell people repressor binds to this site, blah blah blah.  It's boring.  What is interesting is to understand how the complementation test supports their mental construct.  And to realize that the construct came first and the test after.  Most people completely misunderstand how science is really done and maybe this will help them see it.  The point about links and references is well-taken and I will work on it when I get a chance.Telliott 21:51, 29 October 2005 (UTC)
 * I agree totally, and your thinking is sound. Maybe it's more a question of presentation? I still think it might be a bit confusing for the uninitiated though. As I say, I think the content of the article is basically sound.Alun 12:25, 30 October 2005 (UTC)

Somebody PLEASE edit this - it's terribly obscure: "The dominance of operator mutants also suggests a procedure to select them specifically. If regulatory mutants are selected from a culture of wild type using phenyl-Gal, as described above, operator mutations are rare compared to repressor mutants because the target-size is so small. But if instead we start with a strain which carries two copies of the lac genes (that is diploid for lac), the repressor mutations (which still occur) are not recovered because complementation by the wild type genes confers a wild type phenotype. Instead, operator mutations predominate." Philbradley 14:02, 9 December 2006 (UTC)

CAP
CAP stands for catabolite activator protein, not cAMP activator protein. Or am I missing something...?


 * It is also known as CRP, or cAMP repressor protein - probably the source of confusion. 71.162.36.220 13:51, 14 December 2006 (UTC)


 * Yes, CAP stands for catabolite activator protein. Also, it is inclear in the diagram when cap is and isnt bound. It appears to be labelled as CAP bound when the blue box representing CAP is not present

image of operon is misleading
The image of the operon may mislead some to think each gene is only a few turns of the helix. Also, the major groove : minor groove ratio should be about 2 : 1. One turn of the helix should be about 3.5 times the width, which looks approximately correct in the figure by eye. —The preceding unsigned comment was added by Albert.tsai (talk • contribs) 20:04, 21 December 2006 (UTC).

How works the conversion of lactose to allolactose?
I have just read the article and I like it very much. But a question came up for me: Lactose has to be converted to allolactose by β-galactosidase, before it is able to bind to the lac repressor (LacI) causing an allosteric change in its shape. But if β-galactosidase is not transcribed due to the action of the repressor, how is the conversion of lactose to allolactose then working. Is it possible, that a small amount of the enzyme is present at any time? I am thinking of an equilibrium that is changed by the presence of one or the other compound. Or did I possibly miss something?

[Katja] 19:09, 10 January 2007 (UTC)
 * You are indeed right that there is a small amount of the enzyme present at any time (for Y, Z and A genes). This is basically the leaky expression, and it is necessary for import of lactose and conversion to allolactose. 84.197.145.92 23:20, 3 June 2007 (UTC)

On being too technical / Not accessible
I think the best way to make this article more accessible would be to add a couple of introductory sentences, in lay language, about why this topic is notable. I'd also like to see a brief explanation of what it means for an operon to be "regulated," as mentioned in the introduction. (E.g., does this mean different genes are expressed, or passed on during reproduction, or something else, depending on the factors mentioned?) -- Super Aardvark 20:52, 14 May 2007 (UTC)
 * Exactly. Yes, but what does it do?? ~user:orngjce223 how am I typing? 23:41, 20 October 2007 (UTC)
 * Keep in mind that a general audience isn't that likely to read this article - it's more something biology students who already know some biology are going to read. Richard001 (talk) 08:49, 21 September 2008 (UTC)
 * I am a biology student - but I think this should still be informative at least...say in directing someone to the biology wiki book.


 * Also - the image used is deceptive. It shows the genes in the DNA double helix - but in reality, the B-Galactosidase gene, and the others, are dozens or even hundreds of base pairs (and therefore codons) long - not one or two.
 * Elwood —Preceding unsigned comment added by 173.19.42.67 (talk) 06:35, 17 November 2008 (UTC)

The I (eye) in lacI looks too much like a lower-case l (elle)
It does. I have no idea how it should be fixed. This entry into the discussion was actually just to confirm which it was (l or I) to people. 143.167.240.191 (talk) 22:53, 2 June 2010 (UTC)
 * To be fair it's a Roman numeral, meaning one. So http://en.wikipedia.org/wiki/Roman_numeral#Unicode says you can do that in unicode. &#x2160; works (edit to see how to do it). I would like to propose that as a change. 143.167.240.191 (talk) 23:02, 2 June 2010 (UTC)

Hi theres an error under the Isopropyl-B-D-thiogalactoside (IPTG) heading. It says that entry is DEPENDENT on lac permease, however this should read that IPTG's entry into the cell is INDEPENDENT of lac permease as it is definitely known that IPTG can enter into the cell without lac permease. — Preceding unsigned comment added by 211.30.181.169 (talk) 10:45, 24 June 2011 (UTC)

Piece of information severely outdated
This article, as well as practically every genetics textbook in the world, has still not caught up to research done 15 years ago that showed that levels of cAMP are in no way related to levels of glucose. Paper citation: Inada et al., 1996, Genes Cells 1:293-301 Mechanism responsible for glucose-lactose diauxie in Escherichia coli: challenge to the cAMP model. http://www.ncbi.nlm.nih.gov/pubmed/9133663 — Preceding unsigned comment added by 143.206.236.187 (talk) 20:12, 27 February 2012 (UTC)


 * Are the conclusions from this research generally accepted? One paper challenging a long held theory doesn't disprove that theory. Ashcanpete (talk) 23:58, 30 August 2012 (UTC)


 * Yes, it is accepted that there is little difference in intracellular cAMP levels in lactose- and glucose-grown E. coli. The textbooks are wrong.  See, a review paper that is cited in the article.  CatPath (talk) 05:47, 8 September 2012 (UTC)

LacI binding to allolactose
The article currently states that since LacI is tightly bound to DNA, then allolactose must bind it while the repressor is still bound to DNA. If allolactose binding stablizes the non-DNA-bound form of LacI, then this likely happens in free solution, not while still attached to DNA. Unless there are some actual enzyme kinetics studies that suggest otherwise, I suggest removing those comments about LacI binding. — Preceding unsigned comment added by Ashcanpete (talk • contribs) 23:52, 30 August 2012 (UTC)

Etymology of lac operon
To the fluent Latin speaker it's quite obvious where the name "lac operon" comes from.

Unfortunately, there aren't that many fluent Latin speakers nowadays. I suggest adding a note saying that the operon was named lac because of its function relating to the substance lactose, which is found in milk. However, I don't know where in the article to add it. 68.173.113.106 (talk) 02:05, 27 May 2013 (UTC)

cAMP
I'm unhappy with the complete removal of the cAMP section. The reason is that the article seems to promote the idea of inducer exclusion when it cannot explain all the observed phenomena in catabolite repression, and it is probably only half correct. From studies of mutants glucose appears to have direct inhibitory influence on the promoter itself that cannot be explained by inducer repression, so we are left with a hole in the understanding of what is going on. I feel that it should have been rewritten rather than completely removed. Hzh (talk) 01:08, 12 October 2013 (UTC)
 * That was me who removed the cAMP sections. I put those sections back in the article.  I'm sorry for taking so long; I intended to restore the passages when I first saw your comment, but I simply forgot about it (no excuses).  As you proposed, I will rewrite those sections (if I ever have the time).  CatPath (talk) 18:03, 11 April 2014 (UTC)

Isn't lac operon is negative inducible instead of repressible?
The Regulation part states that "The type of regulation that the lac operon undergoes is referred to as negative repressible". However, the operon article says that "The lac operon is a negatively controlled inducible operon, where the inducer molecule is allolactose." — Preceding unsigned comment added by 194.150.65.253 (talk) 11:50, 15 May 2015 (UTC)
 * Thank you for catching that. I corrected the error.  CatPath (talk) 04:12, 16 May 2015 (UTC)

Assessment comment
Substituted at 21:31, 29 April 2016 (UTC)

Alternative (correct?) view
Could mention be made of the view that the lac operon model is possibly a lab artefact? E. coli in nature probably doesn't encounter lactose. It is, however, exposed to a plethora of plant degradation products - including galactolipids. Beta-galactosyl glycerol is perhaps the true inducer of the operon and the substrate of the beta-galactosidase enzyme, rather than lactose. See: The 'lac' operon: an irrelevant paradox, TIG February 1988, Vol. 4, no. 2. Zwirko (talk) 21:37, 12 July 2016 (UTC)
 * I don't think this should be mentioned unless there are well-cited sources that present the same viewpoint. The TIG source is a letter to the editor.  According to Google Scholar, no journal article has ever cited this letter, suggesting that the author's views have been ignored by the field.  CatPath (talk) 19:59, 14 July 2016 (UTC)

== lac I is part of the lac operon!!! == lac I is actually part of the lac operon. This is according to Raven et al.'s textbook. Image = wrong.35.16.127.8 (talk) 21:48, 27 March 2017 (UTC)

Wrong paragraph about reason for basal expression
The following paragraph is wrong:

"However the lactose metabolism enzymes are made in small quantities in the presence of both glucose and lactose (sometimes called leaky expression) due to the fact that the LacI repressor rapidly associates/dissociates from the DNA rather than tightly binding to it, which can allow time for RNAP to bind and transcribe mRNAs of lacZYA. Leaky expression is necessary in order to allow for metabolism of some lactose after the glucose source is expended, but before lac expression is fully activated."

It is true that when both glucose and lactose are present, there is some expression of the enzymes, but not for the reason given above, since the LacI repressor is not bound at all in the presence of lactose. Rather, the reason for leaky expression is that the RNAP can still sometimes bind and initiate transcription even in the absence of CAP. 2804:14C:6181:8747:E485:499A:9C0B:FD61 (talk) 18:43, 24 January 2023 (UTC)