Godless Canadians

 
According to a recent poll, 23% of Canadians do not believe in God [Quarter of Canadians don't believe in any god, poll says].

Here's a summary of the findings ...

The Harris-Decima poll also indicated:

• Women (76 per cent) were more likely than men (67 per cent) to say they believed in a god.
• Canadians over the age of 50 (82 per cent) were far more likely than those under the age of 25 (60 per cent) to say they believed in a god. More than one in three (36 per cent) of those under the age of 25 said they did not believe in any god.
• English Canadians (73 per cent) were more likely than French Canadians (67 per cent) to say they believed in a god.
• Belief in a god is higher in rural Canada (76 per cent) than in urban Canada (69 percent).

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[Hat Tip: The Unexamined Life]

Best College Atheist Groups

 
The Guelph Skeptics at the University of Guelph won $300 from the Student Secular Alliance for Best Media Appearance.

They were in the campus newspaper once, then twice. They were in their local city paper, and most impressively, they are hosting their own radio show in Canada. They’re working on getting the show syndicated so they can play is across North America (it already airs in Guelph, in Victoria, BC and Winnipeg, MB).

Katie Kish of the group says: “With our own radio show we’ve had interviews with each of us on it, interviews with our speaker, coverage of our events. Hopefully it’ll all be podcasted soon.”

Cool.

One of the newspaper articles was about me! [How do you solve a problem like Moran?] It seems like a pretty fair representation of my talk at Guelph.

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[Hat Tip: Friendly Atheist]

Are Science and Religion Compatible? AAAS Says Yes.

 
This is a short video produced by the American Association for the Advancement of Science (AAAS). This is the organization that publishes Science.

The video features Francis Collins and others who promote the idea that religion and science are compatible.

Here's the question; why is the AAAS taking a position on this issue? Why aren't they also producing a video to present the other side; namely that science and religion are not compatible? I'm especially interested in hearing from John Pieret because he is highly critical of scientists who venture opinions about religion. John, does your criticism extend to an organization of scientists like AAAS who are taking sides in a controversial non-scientific debate? You wouldn't be happy if they came down on the side of incompatibility, is this any better?

It seems to me that organizations like AAAS should remain neutral in the debate about whether science and religions are compatible. It's okay for them to point out that intelligent design isn't science and it's okay to criticize astrology and quack medicine, but I don't think it's okay to say that the beliefs of Francis Collins (and others) are compatible with science. I don't think it's okay to promote the evangelical Christian views of Collins and not the atheist views of Richard Dawkins.

Does this meant that it will be difficult to publish an incompatibility article in Science because it contradicts official AAAS policy?

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[Hat Tip: Framing Science, because Nisbet thinks this is a good frame.]

How Many Biochemists Does It Take ....

 

... to fix a projector?

At one point during yesterday's talk the projector and Lewis Kay's powerpoint presentation failed to communicate with each other. That's Lewis behind the podium shortly after the problem was fixed. Helping him were, from left to right, David Isenman, Jacque Segall, Charlie Deber, and Peter Lewis.

They are all Mac users so they're used to this kind of tag team effort to solve computer problems. They do it quite often.

There were no glitches with the Windows operating systems.

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Biochemistry's 100th Birthday: Day 2

 
Day 2 of the Department of Biochemistry 100th Anniversary Symposium began with a series of lectures by former graduates of the department; Shelagh Ferguson-Miller (Michigan State University), Natalie Goto (University of Ottawa), and Mark Glover (University of Alberta).

This was followed by a talk on the early history of the department by Professor Marian Packham. Marian was a student in the department from 1946-1949 and then she did her Ph.D. in the department. After a postdoc and a few years working for the government and the Red Cross, she joined the department as a faculty member in 1966 and rose to become a University Professor in 1989 (our highest title). Professor Packham gave an entertaining summary of the early years complete with humorous anecdotes that I won't repeat here.

Following Marian's talk we heard from two current members of the department: Lewis Kay and Lynn Howell.

The early afternoon was devoted to the poster session, featuring posters from students and postdocs. More than half the graduate students presented posters. One of my colleagues suggested that the high participation rate was due to the prize money being given out. Students have a 12.5% chance of winning at least $250. I'd like to think that they were motivated by a desire to communicate good science and just as many would have turned out if the prizes were just a handshake from our Chair.

I took a picture of Professor Packham at the poster session.

The speaker in the afternoon session (Theo Hoffman Lecture) was Greg Petsko from Brandies University in Boston (USA). Petsko is one of the gurus of structural biology. He has many connections to our department through his former students, postdocs and colleagues. He spoke on the structure of enzymes involved in Parkinson's disease.

Greg Petsko is as proud of his teaching as he is of his research accomplishments—and that's saying a lot. He is a very entertaining speaker. At the end of his talk everyone wanted to rush back to the lab to solve neurodegenerative diseases since many of us are going to get them. That was the main point.

The day ended with a gala banquet at Hart House that lasted until midnight. A very, very good time was had by all. There was plenty of opportunity to experience the products of anaerobic metabolism in yeast.

The person in the photo is John Challice, a former graduate student in our department and currently Vice President and Publisher Higher Education for the U.S. division of Oxford University Press.

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Telomeres

 
Telomeres are sequences at the ends of linear chromosomes that protect the essential part of the chromosome from damage following repeated rounds of DNA replication.

Because of the way DNA replication works, it is impossible to replicate both stands of parental DNA right to the very end. Consequently, after each round of DNA replication the chromosome loses a little bit of DNA and the ends get shorter and shorter.

The telomere consists of multiple copies of repetitive DNA. In the case of humans, the repeat is (TTAGGG)_n where "n" is usually between 1500-2000 in germ line cells. Thus, the average telomere is about 10 kb (10,000 base pairs) in length (Riethman 2008).

THEME

Genomes & Junk DNA

Total Junk so far

    54%
After every cell division the telomere gets a little shorter so that in old individuals the average length is reduced to about 2-3 kb in most somatic cells. The original length is preserved in germ line cells.

There are 23 chromosomes in humans. If the average telomere length is about 10 kb then the total amount of TTAGGG repeats is 230 kb, or far less than 1% of the genome. Even if the total amount of essential sequence at chromosome ends is increased to include adjacent regions, it won't even come close to a significant percentage. Thus, while telomeric DNA is essential non-coding DNA—and not junk— it doesn't change our calculation.

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[Image Credit: The image shows human chromosomes labelled with a telomere probe (yellow), from Christoher Counter at Duke University.]

Riethman, H. (2008) Human Telomere Structure and Biology. Annual Review of Genomics and Human Genetics 9: epub ahead of print [doi:10.1146/annurev.genom.8.021506.172017]

Biochemistry's 100th Birthday: Day 1

 
Yesterday was the first day of our department's 100th birthday party celebrations [Department of Biochemistry 100th Anniversary Symposium].

About 250 people showed up. It was fun to meet former students and retired faculty members, some of whom I hadn't seen for 10 or 20 years.

The first Connell Centennial Lecture was given by James Rothman of Columbia University (soon to be Yale University). His title was The biochemical basis of vesicle transport in the cell.

No matter how many times you hear him talk you can't fail to be impressed by Rothman's style and his ability to present complex material in a manner that can be understood by everyone in the audience. It was a wonderful way to begin our celebrations.

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Tangled Bank #106

 
The latest issue of Tangled Bank is #106. It's hosted at ars technica [Welcome to the 106th Tangled Bank].

Greetings, and welcome to Nobel Intent, the corner of Ars Technica devoted to science. For those Tangled Bank readers who have never stumbled across Ars before, it's a large, tech-focused site that takes its science seriously. We have six science writers here, with backgrounds in planetary science, physics, chemistry, materials science, and biology, and we set them free daily on whatever bit of science catches their fancy. Check things out once you've feasted on the content of this edition of the Tangled Bank, a carnival of science blogging content.

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If you want to submit an article to Tangled Bank send an email message to host@tangledbank.net. Be sure to include the words "Tangled Bank" in the subject line. Remember that this carnival only accepts one submission per week from each blogger. For some of you that's going to be a serious problem. You have to pick your best article on biology.

Science Fiction and Intelligent Design

 
Peter Kazmaier (photo, left) is a research scientist for some private company. He is also an Adjunct Professor of Chemistry at Queen’s University in Kingston, ON (Canada). Kazmaier is the author of a science fiction novel called The Halcyon Dislocation.

Peter Kazmaier has a blog. He recently posted some comments that were picked up by Denyse O'Leary. Here's what Kazmaier says on Who is ‘Galileo’ in 2008? Limitations of Science II.

Recently a film has been released Expelled! No Intelligence Allowed. In it Ben Stein and the producers argue that this very process of suppression is operating in the area of investigation into Intelligent Design. An excellent interview of Ben Stein and others can be found on the website for ListenUp tv.

I have listed the way in which 2008 science is even more susceptible to suppression than science in Galileo’s time. Are there any advantages on the side of those who believe they are being blocked? Yes there are. Through the democratization of knowledge, it is much easier to disseminate ideas today than in Galileo’s time. One can circumvent the journal refereeing process and publish the information directly through books, movies, or the internet.

So what are the personal messages for me to take away from this? First of all I need to understand and follow up the claims made by Expelled. Secondly, as I referee articles, I need to be aware of my own prejudices and biases and not allow them to influence my comments. Finally, at every turn I need to oppose suppression of free discussion of scientific ideas, whatever their source.

I really hope he will follow up on the claims made by Ben Stein in the movie Expelled. I look forward to seeing another post in the next few days where Kazmaier admits that he has been duped by the IDiots. That's what I expect from a Professor at Queen's.

It's true that we need to avoid suppression of good scientific ideas. That's always a given in science. On the other hand, the importance of free expression and skepticism is only manifest if we are able to freely speak out against bad science and bad ideas. There's no rule that says we have to praise every idea just because it claims to be science.

The mark of a good scientist is to be able to separate the potentially good ideas from those that are just plain silly. Offering tacit support to Ben Stein is not a good beginning.

In addition to being a scientist and a writer of science fiction, Peter Kazmaier is also a member of The Word Guild. Here's their mission statement.

Our goal is to impact the Canadian culture through the words of Canadian writers and editors with a Christian worldview. We will do this by connecting, developing and promoting Canadian writers and editors who are Christian.

Hmm ... I see why Kazmaier is so worried about bais when he says, "I need to be aware of my own prejudices and biases and not allow them to influence my comments."

Denyse O'Leary is on the Board of Directors of The Word Guild. Now I see why she promotes Kazmaier on her blog(s). I bet it has something to do with prejudices and biases.

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Nobel Laureate: Wendell Stanley

 

The Nobel Prize in Chemistry 1946.

"for their preparation of enzymes and virus proteins in a pure form"


Wendell Meredith Stanley (1904 - 1971) was awarded the 1946 Nobel Prize in Chemistry for purifying and crystallizing tobacco mosaic virus (TMV). Stanley shared the Nobel Prize with James Sumner and John Northrop who purified and crystallized the enzymes urease and pepsin, respectively.

Stanley's work seemed to indicate that the infectious agent in TMV was a protein, in spite of the fact that TMV was known to contain RNA. You can see from the presentation speech below that back in 1946 the prevailing consensus favored protein as the genetic material. We now know that in 1946 there was a small group of scientists who were thinking that nucleic acid was the genetic material and not protein.

The presentation speech was delivered by Professor A. Tiselius, member of the Nobel Committee for Chemistry of the Royal Swedish Academy of Science.THEME: Nobel Laureates

Your Majesty, Royal Highnesses, Ladies and Gentlemen.

In 1897 Eduard Buchner, the German research worker, discovered that sugar can be made to ferment, not only with ordinary yeast, but also with the help of the expressed juices of yeast which contain none of the cells of the Saccharomyces. The discovery was considered so important that in 1907 Buchner was awarded the Nobel Prize for Chemistry.

Why was this apparently somewhat trivial experiment considered to be of such significance? The answer to this question is self-evident, if the development within the research work directed on the elucidation of the chemical nature of the vital processes is followed. Here, as in other fields of research, progress has taken place step by step, and the conquest of new fields has often been very laborious. But there, more than in most fields, a tendency has showed itself to consider the unexplained as inexplicable - which is actually not strange where problems of life and the vital processes are concerned. Thus ordinary yeast consists of living cells, and fermentation was considered by the majority of research workers - among them Pasteur - to be a manifestation of life, i.e. to be inextricably associated with the vital processes in these cells. Buchner's discovery showed that this was not the case. It may be said that thereby, at a blow, an important class of vital processes was removed from the cells into the chemists' laboratories, to be studied there by the chemists' methods. It proved, too, that, apart from fermentation, combustion and respiration, the splitting up of protein substances, fats and carbohydrates, and many other similar reactions which characterise the living cell, could be imitated in the test tube without any cooperation at all from the cells, and that on the whole the same laws held for these reactions as for ordinary chemical processes. But - and this is a very important reservation - this was only possible if extracts or expressed juices of such cells were added to the solution in the test tube. It was then natural to assume that these cell juices or cell extracts contained some substance which had the capacity of initiating and maintaining the reactions and guiding them into the paths they follow in the cell. These unknown active substances were called enzymes or ferments, and the investigation of their effects became one of the principal problems of chemistry during the first decades of this century, which for the rest it still is.

The important question of the nature of the enzymes remained unsolved, however, in spite of the energetic efforts of the research workers. It is manifestly a question of substances of complicated structures, which are present in such extremely small amounts that they, so to speak, slip through the fingers when one tries to grasp them. It is really remarkable to see how far it was possible to get in the study of the effects of the enzymes and the course of the enzymatic reactions, without knowing anything definite about the nature of these very active substances, nay, even without even being quite clear that they were substances which could be isolated in the pure form at all.

In 1926, however, in connection with his studies of a special enzyme "urease", James B. Sumner of Cornell University, Ithaca, U.S.A. succeeded in producing crystals which exhibited strikingly great activity. The basic material was the bean of a South American plant, Canavalia ensiformis, in America called the "jack bean", and the crystals had an activity that was about 700 times as great as that of bean flour. What was still more important was that it was possible to dissolve the substance and re-crystallize it several times without its activity being affected. The crystals proved to consist of a protein substance. Sumner expressed the opinion that in reality this protein substance was the pure enzyme.

As is so often the case with important discoveries, this result will probably to a certain degree have "been in the air", in that at the time it had been assumed in many quarters that the enzymes were protein substances of quite a special nature. On the other hand, Willstätter, the German chemist and Nobel Prize winner, had carried out far-reaching purifying experiments with enzymes and had arrived at results which caused him to doubt whether it was a question of protein substances or carbohydrates at all. We know now that this was due to the fact that Willstätter's purifying methods yielded solutions which were all too weak for it to be possible for chemical reactions to give a definite result.

For the chemist crystallization is the final goal in the preparation of a substance in pure form. Even though crystallizability is not such a reliable criterion of purity in the case of protein substances as in that of simpler substances, nevertheless Sumner's results have now been accepted as verified and thus also accepted as the pioneer work which first convinced research workers that the enzymes are substances which can be purified and isolated in tangible quantities. Thereby the foundation was laid for a more detailed penetration of the chemical nature of these substances, on which an understanding of the reactions taking place in living cells must finally depend.

Sumner's pioneer work was not immediately followed by similar work in other quarters, which might perhaps have been expected. About three years after Sumner's work had been published, however, Dr John Northrop of the Rockefeller Institute at Princeton began to work on the purification of the protein-splitting enzymes met with in the digestive apparatus and gradually succeeded in obtaining a number of them in crystallized form, e.g. the pepsin met with in the gastric juice and the trypsin and chymotrypsin in the pancreas. Northrop and his collaborators, among whom should be mentioned in the first place Kunitz, also made extremely comprehensive studies of the homogeneity and purity of these purified enzymes, and in that connection gave further proof of their nature as protein substances. Exceedingly interesting results were attained also in the isolation of some protein substances which appeared to be the mother substances of these enzymes. On the whole Northrop used his purified material for detailed chemical studies to a greater extent than did Sumner, and his contributions in the matter of working out the most satisfactory conditions for the crystallization of enzymes have been of the greatest importance for subsequent research workers.

This year's third Nobel Prize winner in Chemistry, Dr Wendell Stanley, first worked at the Rockefeller Institute in New York but moved in 1932 to the department of that Institute at Princeton. The problem which attracted his attention, namely the chemical nature of the viruses, was to a certain degree analogous to the problem of the enzyme just mentioned. As is well known, viruses are contagia which give rise to a large number of the best known illnesses in man, animals and plants, e.g. smallpox, infantile paralysis, influenza, foot-and-mouth disease, mosaic disease (on tobacco plants), etc. The virus particles are invisible in the microscope, and when Stanley began his work, they could only be identified by the symptoms of disease which they occasioned. Thus the problem was more difficult, inasmuch as the effect of the virus could not be as easily measured as that of an enzyme, where an exactly known chemical reaction can be employed. Stanley first tried to show the protein nature of viruses by studying how the virus of the tobacco mosaic disease was attacked by protein-splitting enzymes, but in 1934 he passed on to attempting to purify that virus by methods similar to those which Sumner and Northrop had employed so successfully for enzymes. In 1945, by using large quantities of infected tobacco leaves, he did succeed in producing small amounts of crystals which were extremely active, and which, after detailed investigation, proved to be the bearers of the virus's activity. Here, too, it was a matter of active protein substances. Subsequently it has been proved that nucleic acid also forms an important constituent of the latter.

It seems as though Stanley's discovery may take us another long step forward along the road towards a closer understanding of the chemical nature of the vital processes, for apart from the fact that in extremely small quantities they can give rise to diseases, the virus substances, like the bacteria, have the capacity to reproduce themselves. It was remarkable enough when Buchner found that certain of the functions of the living cell can be separated out from it and are to be found in the expressed juice, but it appears still more remarkable that the capacity to reproduce - this unique characteristic of life - can also be exhibited by certain molecules, thus by dead substances. It must be borne in mind, however, that, as far as we know now, this capacity is only possessed by the virus molecule when it is in contact with the living cell, and that probably the latter is materially responsible for the reproduction of the virus substance.

Investigations both by Stanley and by other research workers show that many kinds of viruses, e.g. the smallpox virus, are considerably more complicated in structure. It is conceivable that the "molecular virus" which Stanley isolated represents the simplest type in a long series of different kinds of viruses which gradually approach the living bacteria. An extraordinarily fascinating field is hereby opened up to research workers, and it is not improbable that development will lead to a closer scrutiny of the border-line between living and dead matter.

Even among scientists we sometimes hear the assumption expressed that the innermost secrets of the vital processes will always be hidden from us, that there is a wall through which we cannot penetrate. Today we do not know whether that be correct, but we know that this wall - if there is one - is considerably farther away than one had dared to believe earlier. That this is so is to an appreciable degree the result of the discoveries which have been rewarded with the 1946 Nobel Prize for Chemistry.

...

Doctor Wendell Stanley. We owe to you one of the most striking discoveries in modern chemistry and biology. The demonstration of the fact that a virus can be crystallized in the same way as many proteins and enzymes, and that it actually is a protein, at once opened up an almost unlimited field of research with fascinating possibilities. You have not only thrown open the portals to this domain, but you are yourself successfully exploring its possibilities, and rich fruits have already been harvested, thanks to your own work and that of your school.

Gentlemen. The fundamental problems which you have attacked and solved with such remarkable success are closely related, and the methods used have much in common. The more recent achievements have added to the significance of the earlier advances in this field. Your work and your discoveries deserve the gratitude of mankind. The award to you of the Nobel Prize in Chemistry for 1946 is an expression of this gratitude.

Doctor James Sumner, Doctor John Northrop, Doctor Wendell Stanley. With the warmest congratulations of the Academy I now ask you to receive your awards from the hands of His Majesty the King.

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Browser Wars: What Browser Do You Use?

 
I started using Netscape about 15 years ago when it first evolved from Mosaic. I kept using the latest versions until just a few years ago when I switched to Firefox—the offspring of Netscape (they use similar Mozilla engines). I never liked Microsoft's Internet Explorer (IE) because it didn't work well on some of the scientific websites. Safari is okay but not as easy to use as Firefox, in my opinion. I'm not that familiar with Opera. (Most bloggers have to have several different browsers in order to make sure their blogs look good for all readers.)

Firefox is about to release a new version and this event is covered on the Scientific American website [The latest version of the Firefox Web browser: Fast and secure]. It's interesting that Scientific American would consider this a newsworthy event. I assume it's because so many scientists are using Firefox?

Anyway, that's not what I want to talk about today. Here's part of the SciAm article.

Where would we be without the ubiquitous Web browser? More than a decade ago, Netscape, AOL and its ilk helped transform the Internet from simply a network of networks to the backbone of modern society by giving users access to anything and everything that was searchable. In typical fashion, Microsoft soon took hold of the Web browser market with Internet Explorer, which chased its competitors down to single-digit market share and borderline irrelevance.

That's the way it was until 1998, when Netscape (battered by Microsoft in the browser wars) decided to share its Mozilla browser software with the public for free. To make a long story short, the public tweaked and improved the software over time until, in 2003, the Firefox Web browser was born. Today, there are about 180 million people using Firefox to navigate the Web, according to Mozilla Corp., formed three years ago to oversee a number of public software projects.

With the Firefox version 3.0 (the latest) only a few weeks away from launching, the Web browser poses a serious threat to Internet Explorer's dominance. As of April, about 40 percent of Web surfers were using Firefox compared with 55 percent relying on Internet Explorer to navigate the Web, according to W3Schools, a Web site that tracks browser usage. Not bad, considering Microsoft held nearly 69 percent of the market at the end of 2005, the first year Firefox started its rise to prominence. (Firefox, which runs on the Windows, Linux and Mac operating systems, was used by about 24 percent of Web surfers at that time.)

One of the advantages of Firefox is that there are many second party add-ons because of the open source nature of the browser engine. Some of these widgets are pretty useful.

I'm not too excited about the upcoming changes in the new version of Firefox but it looks like other people might be more impressed. The trend is clear. Firefox is on the verge of displacing IE from it's dominant position.

Here's the question. What browser do you use? You can answer in the poll found at the top of the left sidebar. Why do you like your browser?

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What's the Difference Between Female DNA and Male DNA?

 
Answer: The "female" DNA sequence is incomplete because it lack DNA from the Y chromosome.

A recent press release from the Leiden University (Netherlands) proclaims Leiden scientists sequence first female DNA.

This is a well-deserved winner of Jonathan Eisen's second Genomics by Press Release Award [Genomics By Press Release Award #2: Lieden University and the First "Female" Genome]. Read the award persentation speech on his blog The Tree of Life.

Congratulations to Leiden University¹ for showing us how science should not be done and how science journalism is taking over from peer review publication.^2.

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1. "Leiden University is the oldest university in the Netherlands. It was founded in February 1575, as a gift from William of Orange to the citizens of Leiden who had withstood a long siege by the Spaniards."

2. We look forward to more press releases when the data is actually published in the peer reviewed literature.

The Blue Watermelon Theory

 
A reader sent me the link to this video with the following comment ...

I came across this movie. It's amazing!!
Please make time to watch it. It'll blow your mind.

We can turn it into a contest.

Question 1: What is the IQ of Shawn? and where did he learn to talk so fast?

Question 2: How many times are the words "false," "falisfiy" and "falsification" used in the video?

Question 3: How come nobody ever told me that evolution has been falsified?


Question 4: Why do we call them IDiots?

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Apologies to those who have seen this video before.

An Amazing Photograph

 
This is an amazing photograph. Phil Plait of Bad Astronomy explains why [Phoenix Descending].

Phil is an excitable guy but you've rarely seen him this excited in a video.

He has good reason ...

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Tobacco Mosaic Virus

 

Monday's Molecule #73 is tobacco mosaic virus (TMV). As its name implies, TMV is a plant virus that infects tobacco and related species. It was one of the first viruses to be identified and one of the first to be purified.

A large number of studies have been done with TMV because it is so easy to purify and because of its simple structure. The virus is composed of 2130 copies of a small coat protein (158 amino acids) wrapped around a single-stranded RNA molecule of 6000 nucleotides.

Stanley won the Nobel Prize in 1946 for crystallizing TMV—a result that was widely interpreted as evidence that proteins were the genetic material (the RNA component wasn't recognized). Watson studied TMV crystals in order to learn about helices. Later on Rosalind Franklin worked on the structure of TMA with Stanley. Aaron Klug worked out the mechanism of assembly based on the demonstration by Fraenkel-Conrat and Williams (1955) that purified coat protein and purified RNA could be mixed and spontaneously reassembled to form active virus particles [See Citation Classic from Oct. 26, 2007].

Later, Fraenkel-Conrat mixed and matched coat protein and RNA from different viruses and used the hybrids to infect plant cells. He showed that the new viruses always had the properties of the RNA and not the coat protein, demonstrating that the genetic material was the RNA and not the protein.

Early workers on in vitro translation uses TMV RNA as a template since it was one of the few examples of pure mRNA.

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[Image Credits: The figures are from Alberts et al. (2002) Figure 3-33.]

Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K. and Walter, P. (2002) The Molecular Biology of the Cell 4th ed., Garland Science, New York (USA)