Wikipedia:Reference desk/Archives/Science/2008 January 28

= January 28 =

Irreversible enzymes?
As a medical student rather well aware of chemistry, I have lately gotten a bit confused about the notion of enzymes catalyzing a reaction only in one direction. For example, hexokinase, an enzyme which catalyses the first step of glycolysis (turning glucose into glucose 6-phosphate), catalyzes the reaction in said direction. This has been referred to (by lecturers etc.) as an irreversible step, a step which is catalyzed in only one direction. The reaction can of course be reversed and is so in gluconeogenesis, where the reaction is catalyzed by another enzyme.

My questions regarding this are:
 * 1) What mechanism allows an enzyme to catalyse a reaction in only one direction?
 * 2) What effect will this have upon the balance of a reaction? While Kc should remain unchanged, adding e.g. hexokinase to a solution of glucose and glucose 6-phosphate should cause the balance to shift away from the equilibrium towards glucose 6-phosphate? OK, this is a bad example, since this step involves the hydrolysis of ATP, but suppose it didn't, or better up that my example was one which involved no other molecules but was otherwise the same, irreversible?

Thanks! ~Linus, 07:40, 28 January 2008 (UTC)


 * Strictly speaking all enzymes catalyze their specific reactions both ways; they do not shift the equilibrium. In the case of hexokinase (and some other enzymes), the reaction is called "irreversible" because the equilibrium clearly favors one side. Icek (talk) 14:22, 28 January 2008 (UTC)

Actually, the truth of the matter is that the equilibrium does not favor one side so clearly all the time. In the case of Glucose -> Glucose-6-phosphate, the hydrolysis of ATP provides a very favorable impetus for the forward reaction, which is why it is considered "irreversible". Nature couples ATP hydrolysis reactions with the reactions that need to go but don't go favorably enough.18.96.7.80 (talk) 16:17, 28 January 2008 (UTC)


 * Yes, ATP is the real secret escape from "catalysts don't change chemical equilibria." In a coupled reaction, you've added a new reactant and new products, and so the chemical equilibrium is changed as the chemical reaction is different. Someguy1221 (talk) 16:29, 28 January 2008 (UTC)

"Down's Syndrome" in animals
Does an analogous genetic disorder to Down's Syndrome exist in other species of animals? --Taraborn (talk) 02:48, 28 January 2008 (UTC)
 * Apparently not. However, this article says that by inserting human genes into lab rats, it may be possible to recreate Down's in other animals. .  bibliomaniac 1  5  02:51, 28 January 2008 (UTC)


 * This website describes some very interesting mouse models of down syndrome, and suggestions on where to find papers on it. Someguy1221 (talk) 02:54, 28 January 2008 (UTC)
 * . This states its in every population. its late. [User:Mion|Mion]] (talk) 02:59, 28 January 2008 (UTC)


 * It's clearly referring to humans only, however. Someguy1221 (talk) 03:03, 28 January 2008 (UTC)
 * I think you're right Someguy,it's the extra 21st chromosome in humans that is named Down's Syndrome, now you can inject a artificial human something into a human/mouse to experiment or mimik effects, its still not the extra 21st chromosome in humans, i think similar errors happen in animals as well, but they have another name, so the answer is no the extra 21st chromosome in humans (down syndrome) is not present in animals. Mion (talk) 03:13, 28 January 2008 (UTC)


 * Some budgerigar breeders claim that the 'feather duster' mutation (which causes constant abnormal feather growth, deafness, blindness and mental retardation and is probably a result of too much inbreeding) is analogous to Down's Syndrome. I'm not sure if there has been any serious scientific research undertaken. --Kurt Shaped Box (talk) 07:35, 28 January 2008 (UTC)


 * Three Cases of Trisomy in the Mouse; A. B. Griffen; M. C. Bunker Proceedings of the National Academy of Sciences of the United States of America, Vol. 52, No. 5. (Nov. 15, 1964), pp. 1194-1198 states that trisomy which means a chromosom is present three times is also possible in mice.--Stone (talk) 07:52, 28 January 2008 (UTC)
 * I was under the belief that the white tiger in some of these pictures had Down's Syndrome but I believe this may be inaccurate and that it simply has a strange appearance due to huge amounts of inbreeding.  Lanfear's Bane |  t  12:15, 28 January 2008 (UTC)


 * Yeah, skull deformity !necessarily= Down's, even though it may look superficially similar. Interesting site though. It contradicts WP's own White tiger article with regards to the claimed 80% infant mortality rate, though... --Kurt Shaped Box (talk) 16:37, 28 January 2008 (UTC)

Is down's syndrome what most people refer to as "retarded"? 64.236.121.129 (talk) 17:09, 28 January 2008 (UTC)


 * Down's Syndrome is one potential cause of Mental retardation in humans. There are others. I don't know if it's considered polite to use the term 'retarded' (in a non-insulting manner) nowadays. --Kurt Shaped Box (talk) 17:19, 28 January 2008 (UTC)

Scientists have actually created a Down Syndrome mouse, it's called the Ts65Dn mouse. As you probably know Down's is caused by trisomy 21 in humans (pretty much all other trisomies are lethal, its seems one of those quirks of nature that human 21 is small enough, and has the right combination of genes, to permit survival if one has an extra copy.)

In other animals, though, genes get scrambled around to different chromosomes during the course of evolution. What the scientists did, was create a mouse with an extra piece of mouse chromosome 16 spliced to an extra piece of chromosome 17. This construct contains 104 of the 231 genes we find on human chromosome 21, and introducing that to mice they modeled the disorder. The result was not a perfect copy of Down's, but it produced mice that live and have the characteristic skeletal changes (a shorter, broader skull and jaw, for instance) and changes in brain structure that are seen in humans with the syndrome.

Since then, scientists have gone on to make mice with ever small numbers of genes, to try and understand exactly which of the 104 are responsible for the characteristics of Down's. Ts1Cje has extra copies of 81 of the genes found on human chromosome 21. Like Ts65Dn it models the human disease pretty well. Ts1Rhr contains just 33 extra genes, and these are the ones found in the human Down Syndrome Critical Region (a stretch on the long (q) arm of human chromosome 21 proposed to be responsible for some, if not all, of the features of Down syndrome). Surprisingly, this mouse didn't have the characteristic features of Downs. They concluded that the disorder is more complex than they had originally thought, and rather than being a result of an extra copy of few genes, the characteristics are a result of interactions between a number of genes. Rockpock e  t  07:25, 29 January 2008 (UTC)
 * Shit. Having written all that I note that someone posted a link to an article above explaining it in much more detail. Oh well. Rockpock  e  t  07:29, 29 January 2008 (UTC)

Depth of ignition
At what depth and beyond will flammable material like clothing and paper inside a submarine hull ignite if the hull collapses? —Preceding unsigned comment added by 71.100.3.254 (talk) 08:00, 28 January 2008 (UTC)
 * I don't have any numbers for you. But, first: check the article on Self ignition. Next you want to measure how hot a gas will get when it's rapidly compressed, for that see Adiabatic compression. The final issue is that things will self ignite at a much lower temperature when the oxygen concentration is high. Now, I'm not sure that increasing the oxygen concentration by compression (not concentration really, but more like oxygen available near the item), is comparable to increasing it by having more oxygen, but it's got to have some effect. Ariel. (talk) 08:37, 28 January 2008 (UTC)


 * To the second part of your response, the answer is yes. In looking at the effective concentration of oxygen, the important term is the partial pressure of oxygen, not its relative fraction.  Take ordinary room air (roughly 20% oxygen, 80% nitrogen) and compress it to a pressure of 5 atmospheres&mdash;that gives a partial pressure of oxygen of 5 atm * 20%: one atmosphere.  Under those conditions, fires will burn essentially the same way they would under 100% oxygen at regular atmospheric pressure.  (For similar reasons, deep-sea scuba divers use gas blends that contain reduced oxygen – heliox or trimix often contain 10% oxygen, for example – to reduce the partial pressure of oxygen that the divers breathe at extreme depths and reduce oxygen toxicity.) TenOfAllTrades(talk) 22:17, 28 January 2008 (UTC)


 * The question makes an untrue set of assumptions. Drawing on personal experience, submarine hulls do not get slowly, steadily smaller as they sink, yet keep their integrity and their shape, their internal volume shrinking, and air pressure increasing.   Yes, there is some tensile yield in the hull, but for all practical purposes it will keep it's size and shape until some component gives way.  At this point, lots of water comes spraying in, and two opposing mechanisms go to work.  On the one hand, the incoming water rapidly fills the "people tank" as we called it, so the air is forced into a decreasing volume and the air pressure rises quickly.  On the other hand, said air volume is also being kept "quenched" by the incoming spray of cold water.  The gripping hand is that a submarine has very little that can actually burn.  Possible fuels are limited to paper, fuel oils, lubricating oils, munitions, and the human body itself.  Prior research - recordings made during the Thresher accident - showed very few noises that could have been called a diesel type fuel-oxygen detonation.  The noises recorded were all the (expected) pops of breaking machinery and implosions of things that held gases but could not withstand the seapressure.  Please note that I have never served on a submarine that suffered a hull implosion while I was there so I have to depend upon other witnesses and records. -SandyJax (talk) 19:57, 29 January 2008 (UTC)

Musical brains
Has any research been done into the structure and function of the brains of composers (as compared to the brains of the rest of us)? I ask because it struck me the other day just how amazing it is to be able to produce new tunes (almost at will in the case of some "tin-pan alley" composers). DuncanHill (talk) 10:29, 28 January 2008 (UTC)
 * The brains of composers are much more succulent than those of ordinary humans. Weasly (talk) 11:16, 28 January 2008 (UTC)
 * On the topic perhaps this link would be useful to you.  Lanfear's Bane |  t  12:05, 28 January 2008 (UTC)


 * Or this one (or this) (must get round to reading this book myself) AndrewWTaylor (talk) 14:28, 28 January 2008 (UTC)

Phage titration / Identify bacteria
I have reading material written by a non-native English speaker and it says that "bacteria [can be] characterised by phage titration" (this is to confirm the integrity of an E. coli K12 DH5alpha culture). What are they trying to say? I think phage titration would be where you determine the number of phage per ml of a solution. Seans Potato Business 10:55, 28 January 2008 (UTC)
 * To test if the DH5alpha cells might have been over-grown by another strain of bacteria (or in some other way become less efficient as a host for the virus), you could test for the efficiency of infection using a virus stock. If all is well, you should see a high efficiency of infection in the test titration. If there is an apparent low rate of infection, then it might be time to grow up a fresh batch of the DH5alpha bacteria from a frozen stock. --JWSchmidt (talk) 04:06, 29 January 2008 (UTC)

Digital modulation transmission rates
I have a doubt about how can I manage the transmission rates on a system designed to allow multiple modulation schemes - for example, systems using the 802.16 standard. If the system uses BPSK I'll have a symbol rate equal to the data rate. If after a while I change the modulation, for example, to 16-QAM, the symbol rate will be 1/4 of the data rate, so, if the data rate remains unchanged, I'll not have a higher transmission rate, so, I wonder if those systems are operated by multiplying the data bit rate by the a constant dictated by the modulation in use (4 in 16-QAM, 6 in 64-QAM, etc.) in order to keep the symbol rate constant. Can you help me with that? Thanks in advance. 84.91.38.179 (talk) 10:58, 28 January 2008 (UTC)


 * I found something. It may answer your Question --TreeSmiler (talk) 02:16, 29 January 2008 (UTC)
 * Thanks, it is just as I expected. If the baud rate changed after changing the modulation scheme it would not be possible to make a fair comparison between them. Thanks. —Preceding unsigned comment added by 217.129.241.169 (talk) 21:50, 29 January 2008 (UTC)

Classifying transformed bacteria (biohazard)
If I was handling, experimentally, a high concentration of a very immunogenic protein, would that pose a risk? I'm a uni student and as part of an assignment, I have to classify E. coli K12 bacteria that has been transformed with ppUL32 of the cytomegalovirus. The bacteria is class I, and the viral protein shouldn't be harmful in "normal" concentrations (the concentration at which it would accumulate in a CMV infection) but the protein is highly immunogenic (the most immunogenic of all CMV proteins). Thus, could the transformed bacteria be classed as class II? As a separate question, does the concentrated protein post an immunomodulatory threat? Seans Potato Business 12:27, 28 January 2008 (UTC)
 * Isn't the E. coli K12 used for educational purposes not the same "bad" E. coli found intestines. According to the escherichia coli article, E. coli K12 "have lost their ability to thrive in the intestine". -- MacAddct &#xF8FF; 1984 (talk &#149; contribs) 20:33, 28 January 2008 (UTC)
 * Yes but it's important to take into account the danger posed by the genetic construct with which it was transformed. All E. coli K12 are not equal - indeed, some will be considered very hazardous and warrant level 4 containment, depending on the way in which they were modified (obviously strains modified in this way aren't used for normal educational purposes). Seans Potato Business 21:44, 28 January 2008 (UTC)
 * What kind of "immunomodulatory threat" are you imagining from this Cytomegalovirus protein? --JWSchmidt (talk) 03:49, 29 January 2008 (UTC)
 * I imagine some sort of harmful over-reaction to the concentrated protein, if it reaches a mucosal surface. Seans Potato Business 11:13, 29 January 2008 (UTC)
 * Um ... Wikipedia's probably not really the best place to be trusting for this sort of advice. (Not that we wouldn't know anything, it's just that were not *that* reliable in our answers - sort of the rationale behind the medical/legal advice rules: I wouldn't bet my life/health on the WP reference desk.) Your university should have a Health & Safety office which deals with research safety issues - I'd ask them. If for some reason your institution doesn't have one, ask around at the Health & Safety office of the nearest Big University. They should be able to give you answers, or if not, be able to talk to people (NIH, CDC, etc.) who would. For the most part, I've found (university) H&S people to be friendly and congenial. Don't worry about incurring their wrath - having a university researcher voluntarily consulting them is such a shock they tend to bend over backwards to help. (University researchers are notorious for ignoring safety regulations - by even considering the safety implications, you're doing far better than the average researcher.) BTW, if you haven't already, take a look at our Biosafety level article. -- 128.104.112.76 (talk) 22:52, 2 February 2008 (UTC)

What major would this fall under?
Lets say I want to build weapons, design new and different engines, cars and other vehicles. What college major would that fall under? 64.236.121.129 (talk) 17:08, 28 January 2008 (UTC)
 * Mechanical Engineering. Possibly aerospace engineering depending on the type of weapons and engines, but mechanical has that whole spectrum.  18.33.0.55 (talk) 17:26, 28 January 2008 (UTC)

British Rail Steam Locomotives
Some Tank engines used the suffix MT, what did the M stand for?90.198.148.196 (talk) 17:09, 28 January 2008 (UTC)


 * How was the suffix used? At LMS locomotive numbering and classification it refers to MT meaning "mixed traffic"; that would be as part of a class designation rather than, for example, a wheel arrangement.  --Anonymous, 23:40 UTC, January 28, 2008.

IMAX lamps -- as hot as the sun?
While waiting for an IMAX film to begin the other day, the trivia section in the beginning informed me that its lamps get as hot as the surface of the Sun. This claim is repeated on the web, e.g. here. Is this possible?

The Sun article says that the surface of the sun is over 5000 °C. At that temperature, isn't just about everything a gas? The article on the bulbs used in an IMAX theater, Xenon arc lamps, mentions that they use "fused quartz" electrodes. While I couldn't find anything on fused quartz, the Quartz article says that it has a melting point of about 1600 °C, well under the temperature on the surface of the sun.

Is their claim likely?

Thanks! &mdash; Sam


 * While you're quite correct that the solid components of the lamp would not survive at five-thousand-degree temperatures, the arc itself can get that hot. The arc is a hot plasma that only slowly conducts heat out to the electrodes and quartz lamp envelope.  (This is why high-powered xenon arc lamps require water cooling&mdash;without it, the electrodes would heat to melting and the lamp would fail.) TenOfAllTrades(talk) 17:52, 28 January 2008 (UTC)


 * Thank you! &mdash; Sam —Preceding unsigned comment added by 63.138.152.238 (talk) 17:59, 28 January 2008 (UTC)


 * You might enjoy our article on Xenon arc lamps, the technology used in the IMAX projectors. And yes, the arc is very hot.


 * Atlant (talk) 23:46, 28 January 2008 (UTC)

How well would modern body armor stand up to musket fire?
Lets say, muskets used during the American Revolutionary War and rifled muskets used during the American Civil War. 64.236.121.129 (talk) 17:46, 28 January 2008 (UTC)


 * Body_armor is relevant. There are many different levels of body armor.  I would suspect that a typical musket of that era is comparable to say, a shotgun slug, in performance.  Pretty much even the wimpy body armor should stop a large, slow-moving. not-pointed projectile.  Speed and shape of the bullet make a large difference. Friday (talk) 17:52, 28 January 2008 (UTC)
 * Sounds about right. The soft non-jacketed lead will also aid energy dissipation. &mdash; Lomn 18:06, 28 January 2008 (UTC)

Do British men have higher pitched voices than American men?
If so, why? 64.236.121.129 (talk) 17:48, 28 January 2008 (UTC)
 * Apparently not. The American Language/Chapter 29. "the American voice in general starts on a higher plane, is normally pitched higher than the British voice". Martinp23 19:04, 28 January 2008 (UTC)


 * I do think that British men are more likely to vary the pitch of their voices. DuncanHill (talk) 19:14, 28 January 2008 (UTC)


 * Compare Prince Charles and George Bush : ) Julia Rossi (talk) 02:59, 29 January 2008 (UTC)


 * Hardly what one might consider a representative statistical sample. :)  --  JackofOz (talk) 03:08, 29 January 2008 (UTC)


 * Perhaps you live in one of those countries, so you often hear one in person, but the other on TV/telephone, which might change the tone. &#x2013; b_jonas 07:51, 30 January 2008 (UTC)

There may be a British tendency for the male voice to rise to a high pitch when bellowing orders in military drill, which is less likely among American soldiers, based on observation of soldiers drilling in London. I have also observed this when British men are yelling about anything. Edison (talk) 02:07, 31 January 2008 (UTC)

Species Identification


I was wondering if anyone could identify the species pictured in Image:South African Insect.JPG; the photo was taken in the Madikwe Game Reserve in South Africa which borders Botswana. —Preceding unsigned comment added by Guest9999 (talk • contribs)


 * It is a foaming grasshopper from the family Pyrgomorphidae. Genus Dictyophorus and probably D. spumans. Colourful South African grasshoppers tend to be poisonous. Take care. (online reference image) -- Lycaon (talk) 23:46, 28 January 2008 (UTC)
 * Thanks for the information. Guest9999 (talk) 01:31, 29 January 2008 (UTC)
 * That's a nice photo you took, Guest9999. -GTBacchus(talk) 00:01, 29 January 2008 (UTC)
 * Thanks. Guest9999 (talk) 01:32, 29 January 2008 (UTC)

β-mercaptoethanol uses
Along with smelling horrendous, I recall using β-mercaptoethanol as an ingredient for a DNA stain. I think it was when we did DNA sequencing. The article does not mention anything about its use in stains. Anyone have an idea? -- MacAddct &#xF8FF; 1984 (talk &#149; contribs) 19:06, 28 January 2008 (UTC)
 * It is an antioxidant that prevents the formation of disulfide bonds in and between proteins. It is used in many biochemical buffers for that reason. Сасусlе 21:00, 31 January 2008 (UTC)