Talk:Hershey–Chase experiment

UMD BIOE120

It was mentioned to us by our professor that we should discuss the recent findings on arsenic based life. While these findings are controversial we do believe the applications to Hershey-Chase are significant and have therefore included the topic in this entry. Jmn49114 (talk) 14:53, 30 March 2011 (UTC)

Additionally, the article cited was peer reviewed and published in "Science". While controversy surrounds the article, this situation is common within the scientific community and the findings have not been repealed by the authors and therefore the content should be considered a valid medium for discussion. Jmn49114 (talk) 21:31, 31 March 2011 (UTC)

Peer Review

PEER REVIEW Team Nine Hershey-Chase Experiment

For Team Nine’s peer review of Team One’s article, we read and edited the Wikipedia article on the Hershey-Chase experiment. Overall, Team One’s article on the Hershey-Chase experiment was very well written and detailed, with a few corrections to be made on organization and content.

First of all, while the opening sentence sums up what the Hershey-Chase experiments were, the last part of the sentence (“which had first been demonstrated in the 1944 Avery–MacLeod–McCarty experiment”) is probably not necessary information to be included; the opener should only include critical information about the experiment, so save this part for another sentence by itself. Also, the first section, which is just an overview of the article, can be shortened, as it is only supposed to provide a brief summary of the Hershey-Chase experiment; some of the detail is a bit redundant, as it is mentioned again under the heading “Methods and Results.’ The information provided in the very first section is too specific and detailed, which should be saved for the later sections and headings.

For the introduction and historical background section, the subheadings are a bit broad and underspecified. While the ‘previous assumptions’ section makes sense in relation to the overall heading of ‘intro and background,’ the sections ‘Need for clarification’ and ‘predictions’ do not say much about the background of the Hershey-Chase experiment. In other words, try to organize the information and details of ‘Need for clarification’ and ‘predictions’ into different headings under “Introduction and background,’ as they are a bit unclear. For example, since predictions are a part of making hypotheses change the ‘Predictions’ section to ‘Hypotheses’ and adjust the paragraph accordingly (which shouldn’t be by too much). In addition, the last sentence under ‘previous assumptions’ is wordy and confusing (“The multitude of functions that can be attributed to proteins was also known while DNA at the time had no known function, so it was sensible for scientists to believe that being genetic material and responsible for inheritance of traits could be just another function of proteins”); try to make the sentence shorter and more straightforward. Overall, the headings in this section are unclear and not very specific, but can be easily adjusted.

The “Methods and results’ section is very good and detailed. It includes all the necessary details about the experiment and does so in a clear and informative manner. This section could be expounded upon by moving some of the details from the very first opening section to this section, as mentioned before. The only other part of this section that could be changed is the ‘Limitations and opportunities for further research’ section; it does not directly relate to the experiment and results, and is instead more of the experiment’s impact on future DNA research. This could be made in to another section at the end of the article, where it ties in more to the implications and applications of the experiment.

Finally, for the “Applications’ section, the paragraphs on crime investigation and genealogy are a bit long and unrelated to the Hershey-Chase experiment itself; try to make these sections shorter and only discuss how the application related to the findings of the experiment. For example, for the crime investigation section, give a brief overview and then keep the last paragraph which relates directly to the experiment.

Overall, the article for the Hershey-Chase experiment is a very well written and in-depth article. The citations and pictures are all very good, and the edits for organization and content will help make the article flow more easily and read more like a scientific article. Cashley1 (talk) 14:38, 12 April 2011 (UTC)

Group Three peer review

The Hershey – Chase experiment was conducted to determine if DNA did in fact contain the genetic code for organisms. It was previously thought that proteins held the genetic information because only the multitude of combinations brought about by the 20 different amino acids in polypeptide chains could represent such a large number of traits in an organism. Hershey and Chase proved that DNA contained the genetic code by labeling phages with radioactive Phosphorus-32 (to track DNA) in one experiement, and with radioactive Sulfur-35 (to track protein) in another, and then allowing the two samples to be adsorbed into the cell. The lack of adsorption of the protein labeled with S-35 and the high rate of adsorption of the DNA labeled with P-32 into the cell proved that DNA is in fact associated with growth.

Comments (Introduction and Historical Background)

• Good background on the previous theories and reasons why they seemed valid.
• They also present applications of DNA as genetic material to highlight the significance of the experiments.
• Under the Need for Clarification section, there is an extra “<” before the footnotes.
• The first part of the article is too technical – there is a lot of repetition with the other parts of the article.The beginning of the article should be more general and easier to understand, and later sections should be used to further explain the technical aspects of the experiment.

Comments (Methods and Results)

• “Establishing Conceptual Baselines” is too specific to be a heading for a Wikipedia page. Try to keep section titles more general. Perhaps merge this section with “Experiment and Conclusions” or “Predictions”
• “most of the P-32 and a heavier solution”
• “Hershey and Chase first needed to determine a viable way of isolating for observation the different parts of the phages they were studying.” - awkward sentence structure.
• “DNA from the phage is inserted into the bacteria shortly after the virus attaches to its host.”
• “This was shown by freezing the bacterial cells after they had been infected which caused cell lysis and the bacteria ruptured enough for the release of most cellular material to occur but none on the phage’s labeled DNA could be detected outside of the bacterial cells.” This is a run-on sentence and is very confusing
• Limitations and Opportunities for Further Research- This section is unnecessary. If you want to keep it, add it to the end of the previous section or explain more in depth what this means.

References

• “Using X-ray crystallography, the structure of DNA was discovered by James Watson and Francis Crick with the help of previously documented experimental evidence of Maurice Wilkins and Rosalind Franklin.[6]”

^ Champoux, James ([2001]). "DNA topoisomerase:Structure, function and mechanism." (PDF). Annual Review of Biochemistry(journal). doi:10.1146/annurev.biochem.70.1.369 The source is cited correctly but does not contain information pertaining to this section of the text.

• The remaining references and citations we checked were accurate.

Minor Concerns (Discussions section)

• Confirmation, Line 2, “…and only said that IT must have…”
• Similar Experiments, Line 3, “…documented experimental evidence BY Maurice…”
• Similar Experiments, Line 3, “…representing one OF the twenty amino acids.”
• Similar Experiments, Line 7, “transcription” is repeated.
• Arsenic -Based Life Forms, Line 5 “…and therefore confirmed the sustained…”

General Comments

• Overall the Discussion section effectively relates its topics to the Hershey-Chase experiment without going into unnecessary in depth analysis.
• Under Crime Investigation, in the Applications Section, the group goes into great detail about the history of forensic sceince and how it transgressed over the century. The last paragraph, however, is the only connection to the Hershey-Chase experiment. It might be preferrable to limit the detail in the first paragraph or to remove it altogether.
• The Geneology section could also be shortened a bit and more effectively related to the Hershey-Chase experiment. For example “…which is heavily relied on by those on a journey to find more information on their ancestry,…” is unnecessary.
• The external links are very helpful and could maybe be emphasized to refer to for further clarification of the experiments.
• The first image displayed does not emphasize that sulfur was used in the making of the protein and that phosphorus was used for the DNA. It only demonstrates which section of the phage were radiocative. The image in the second external links does however distinguish this, so maybe it should be used instead. Xcnunes10 (talk) 22:11, 12 April 2011 (UTC)

Group Three 2nd peer review

The introductory section was condensed and the numerous technical terms were taken out, as suggested. Overall, a lot of repetitive information was removed throughout the article, making the section much easier to understand. The addition of the new color-coded diagram does a better job in depicting the experiment.

Of the five minor concerns listed in the Discussions section, only two of them were adhered to. We still suggest changing the other three and proofreading the article for other grammatical errors. The Legacy section is well condensed and mentions effectively how the Hershey-Chase impacted future discoveries and technology.

The removal of many of the subsections under “Methods and Results” made the section a lot clearer and more concise. Now the section is shorter and confusing sentences were fixed, so the section is more focused and comprehensive.

Wiki-links should be used the first time a word appears in the article. For example “adsorption” appeared several times in the article before it was wiki-linked. Xcnunes10 (talk) 23:31, 2 May 2011 (UTC)

Group Nine 2nd Peer Review

I like the overall format of this article. Everything flows together well, and the redundancy was limited to the fact that DNA was the genetic material. I had a little trouble understanding the information, as it was portrayed very concisely. The pictures were helpful and fit into the article nicely.

The only major problem I have is that you used very limited number of sources (I count actually 1) to write your Introduction, Historical Background, and the Methods & Results sections. I understand that that source is the actual publication by Hershey and Chase, but it would be nice to have some follow-up experiments that verified some of the information that you address. Either way, some of the facts that you wrote were not cited at all in those three sections.

For minor concerns, I changed two little typos for you. If you go to history, you will find that "yshin14" username has changed like two little things. But, I do want you to consider rewording this part in the Hypothesis section: "since the element phosphorus does not exist in protein but does in DNA". I feel that this revision would be better: "...because the elemental phosphorus exists in DNA but not in protein". Also, reword this from the Methods & Results section: “It was found that these “ghosts” could adsorb to bacteria that were susceptible to T2, even though there was not DNA contained inside the structures”. The second portion of this sentence is written awkwardly.

Going back to the positives, I do like your Confirmation section in the end along with the added section on the arsenic-based life form. I'm not sure if it goes outside the scope of this Wikipedia article, but it is definitely interesting. Overall, excellent Wikipedia article; very professional.

Yshin14 (talk) 21:15, 3 May 2011 (UTC)

RE: Peer Reviews

Group 9 Review

I do not think this sub heading should be changed because it does not simply say "background" but "historical background" and so in that we are implying that we are talking specifically about the historical events leading up to the experiment and not the background of the experiment itself. — Preceding unsigned comment added by Richard.le12 (talk • contribs) 03:04, 23 April 2011 (UTC)

Group 3 Review

I did not change the name of the "Establishing conceptual baselines" section because I think it accurately describes the goal of the section. Hershey and Chase lay out in their article the procedures they took just to be ABLE to preform their experiment. These preparations were not part of the experiment itself but were required in order to be able to achieve any significant conclusions from their results. This process was a conceptually new idea based on observations from previous research by themselves and others and therefore merits its own section. Jmn49114 (talk) 15:28, 24 April 2011 (UTC)

Group 3 Review

The citation for the use of X-ray crystallography in the determination of the structure of DNA is updated with a more recent article published by The American Institute of Physics in Mar 2003. This publication clearly indicates that Watson and Crick could not have proposed the double helix structure of DNA without accessing the experimental results obtained by Rosalind Franklin.Mengew79 (talk) 04:42, 25 April 2011 (UTC)

Prediction vs hypothesis

Please note that a hypothesis is a statement about the phenomenon that answers a research question. Usually it's broad in scope. In this case, the hypotheses are "DNA is the genetic material (of T2 phage)" and "protein is the genetic material." Statements about what should happen in a specific experiment if the hypothesis is correct are predictions, not hypotheses. Predictions should be phrased as "If hypothesis A is true and experiment B is performed, then result C should occur." They aren't phrased as "If you get result C, then hypothesis A must be true." For one thing, it's always possible that result A could be accommodated by some other hypothesis -- which is why we say that hypotheses are supported, not proven, when they make correct predictions. Agathman (talk) 20:16, 29 March 2011 (UTC)

MSH

I see that this article has been nominated for review as a WP:Good article. It's technically not required for GA status, but Wikipedia's Manual of Style specifies sentence case rather than title case for the capitalization of section headings. (See WP:MSH for the full description.) It's not part of the GA criteria, but it might be just as well to change it. Good luck, WhatamIdoing (talk) 00:50, 3 April 2011 (UTC)

Inaccuracies

Sadly, this article is full of inaccuracies. The Applications section, which I have hidden, describes techniques which are not at all related to the experiment. This has already been mentioned at the Peer Review. To say that most biologists believed proteins carried the heredity material in not true. Following the work from Avery's laboratory in 1944, and by the time Hershey and Chase published their results in 1952, the belief that DNA was the genetic material was widespread. That's why Crick, Watson and others were so keen to determine the structure of DNA. Hershey and Chase were not convinced by their results and wrote, "Our experiments show clearly that a physical separation of the phage T2 into genetic and non-genetic parts is possible...The chemical identification of the genetic part must wait." They published there results at the same time Watson and Crick published there DNA model in Nature, so timing was in Hershey and Chase's favour. I think the article is overstating the importance of the experiment. It was not essential to our subsequent knowledge about DNA, it just provided a little more evidence of the role of DNA in biology—a role that was already widely accepted by the time of publication. Most textbooks only devote one or two pages to this subject, the claims currently made in this article are exaggerated and are not and cannot be supported by sources. Graham Colm (talk) 16:15, 24 April 2011 (UTC)

Re: Inaccuracies I tried to address when exactly biologists were uncertain about what was hereditary material, by adding "prior to the Avery–MacLeod–McCarty experiment in 1944" to the sentence in question. Homedog21 (talk) 02:20, 25 April 2011 (UTC)

I see that my edits that were made in attempt to restore the balance of the article have been reverted. [1] As a result the section on the historical background now contradicts itself. No page number is given for the Matthew Cobb; Morange, Michel (1998) citation, but this book does say this: "Early studies of molecular biology attributed the discovery of the genetic role of DNA to Hershey and Chase. It took protests from Avery's colleagues for his experiment to be restored to the pantheon of molecular biology. Even today molecular biology textbooks often put the two experiments on equal footing, ignoring the fact that they took place eight years apart". (My emphasis). This was written in 1998, modern textbooks do not perpetuate the myth, (See Lewin's Genes X, ISNB 9780763779924 pages 5 to 6, for example). The Lead section of the article gets the balance more or less right, but the first sentence of the historical background contravenes WP:NPOV and has unsupported attributions and weasel words. This is not how Good Articles are written.Graham Colm (talk) 18:22, 1 May 2011 (UTC)

I have tried to simplify and correct the "Historical background" section so that it does not contradict itself. I have stated simply that originally, proteins were thought to be genetic material, then the Avery-Macleod-McCarty experiment provided support for DNA as genetic material, which led to the Hershey-Chase experiment. Homedog21 (talk) 21:25, 1 May 2011 (UTC)

And the section is so much better. Simple statements of fact will really improve this article. We must try to avoid over-selling history. Graham Colm (talk) 21:48, 1 May 2011 (UTC)

Image

Depending on your language skills, it might be worth looking at versions of this article on other language Wikipedia pages. Anyhow, this image [2] is quite good. It does not seem to be available on the Commons, so if you decided to use it, it needs copying across. Graham Colm (talk) 08:25, 25 April 2011 (UTC)

That is a good image. I am still in favor of using different colors for different radioactive isotopes (32P and 35S). If you can get access to the source file and edit it, that will be great. UM BIOE120 Instructor (talk) 13:41, 26 April 2011 (UTC)

How about this?

Graham Colm (talk) 18:18, 26 April 2011 (UTC)

Thanks, and good work. I have incorporated this image into the "Experiments and conclusions" section. It can be further edited (or potentially moved to another part of the article if it seems redundant) if necessary. Homedog21 (talk) 02:49, 27 April 2011 (UTC)

Comparisions with protein analysis

Please be careful with comparisons to protein analysis, particularly in regard to DNA fingerprinting. This technique exploits variability in non-coding regions of DNA, i.e. DNA that is not used to direct protein synthesis, see Variable number tandem repeat). I have hidden some inaccurate statements. Please bear in mind that students all over the world will be reading this. Graham Colm (talk) 20:40, 29 April 2011 (UTC)

GA Review

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

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This review is transcluded from Talk:Hershey–Chase experiment/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: SpinningSpark 17:26, 29 April 2011 (UTC)

Please do not strike any of my comments - I will do that as the points are addressed. If you feel you need to indicate which points you have addressed please use some other method (text, graphic symbol eg tick etc)

There are a few edits that have occured since I started reviewing which are concerning;

• Unsourced text added to Legacy section [3]
• Some text in Legacy section placed in hidden tags[4] - are the claimed issues with this text going to be addressed?

Lede

• The dates in the lede (1952 and 1869) do not appear in the body of the article and are not cited (WP:LEAD issue)

Historical background

• "Before Hershey and Chase provided further evidence..." This is the first sentence of the article, there has been no discussion of what prior evidence existed. The sentence thus lacks context.
• The last sentence of the first paragraph is uncited - I assume that cite 2 covers the rest of the paragraph, not just the text it is attached to.
• "Avery–MacLeod–McCarty experiment" it is implied in the sentence that, but not explicit, that scientists then stopped believing that proteins were the genetic material. If that is what is meant, it should be explicit.
• The whole paragraph is confused, not least because the sentences are out of historical order. I can help copyedit, but the facts need to be clear first. If scientists stopped believing the answer was protein in 1944, how is it "...a few still believed that proteins..." is stated - is that 1862? 1944? or 1952? And who are these few?

I am pausing further review for now and putting the GA on hold as there has been no response on this page. The article seems to be simultaneously undergoing a peer review at this time. It is not sensible to conduct two reviews at the same time in this way and it may be best to withdraw the GA nomination for the time being. SpinningSpark 00:22, 6 May 2011 (UTC)

In view of zero response on this page from the authors, this nomination is failed. SpinningSpark 22:02, 19 May 2011 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Arsenic-based life forms

I see my concerns over the inclusion of this section have been ignored and my edits reverted. I remain completely unconvinced that this material belongs in the article. It has nothing to do with the experiment. It might, in time, be worthy of a new article, but it does not belong here. Readers who come to Wikipedia to read about the Hershey-Chase experiment will not be interested in this tangential discussion. I shall delete the aforementioned section. Please do not restore this material without further discussion and consensus. Graham Colm (talk) 20:23, 21 May 2011 (UTC)

Of course you are correct. The same information was added to Felisa Wolfe-Simon (diff—I reverted that addition because it appeared to be a list of items chosen by an editor to show defects in a paper, which is not appropriate in a BLP). Johnuniq (talk) 09:04, 22 May 2011 (UTC)

Injected DNA was not integrated into the bacterial DNA

I just deleted the following:

However, once the DNA was inserted, it did not remain in the cytoplasm of the bacterial cell but was incorporated into the bacteria in some fashion (later determined to be inserted into bacterial DNA). The infected bacterial cells were frozen to cause cell lysis and the release of most cellular material. Upon examination, almost all of the phage’s labeled DNA was found to have been incorporated into the bacterial cells.

Bacteriophage T2 is virulent virus and is incapable of being inserted into the bacterial DNA, as is the case for lysogenic bacteriophage such as Bacteriophage lambda. In fact, the T-even bacteriophages degrade the host chromosome as part of their life cycle. The DNA from the infecting phage is used as the template strands for the semi-conservative DNA replication for production of progeny phage. The nature of the DNA replication systems of T-even phage means that the parental DNA will be fragmented among progeny molecules by recombination. Interestingly, the experiment to show phosphate in the progeny is cited in the text with no data shown. They were not the first to show DNA phosphate transfer between generations - they cite earlier work on page 52. --JimHu (talk) 23:41, 3 February 2014 (UTC)

wrong picture for Martha Chase

The picture of Martha Chase is in fact a picture of Charlotte Auerbach : https://en.wikipedia.org/wiki/Charlotte_Auerbach 192.41.114.225 (talk) 11:22, 9 October 2023 (UTC)