cmccaff@urbana.mcd.mot.com (Chuck McCaffrey) (04/05/90)
In article <1990Apr2.191538.8552@Solbourne.COM> taylor@anthrax.Solbourne.COM (Dick Taylor) writes: In article <3954@plains.UUCP> jarvi@plains.UUCP (Trent BIOLOGICAL Jarvi) writes: >... >Is it possible that the heart is another 'lobe' of the lungs? >That still would not explain the question about the heart being on the left > >Trent Jarvi ivraJ tnerT It would seem unlikely. The heart, after all, is different in structure, function, and connection to the outside world. It was interesting (and a good way of remembering which lung had how many lobes) to note that the tricuspid valve (between the right atrium and right ventricle of the heart) has three lobes, where the mitral valve (between the left atrium and left ventricle) has two. Does anyone else know of 3:2 asymmetries in the body? Are they also 3-right/2-left? ---- The heart also comes from different embryologic tissue. While it is true that the tricuspid valve (right side) has three cusps (hence its name) and the mitral valve (left side) has two cusps (it is also known as the bicuspid valve), I don't believe that this 3:2 structure is more than coincident with the fact that the right lung has three lobes and the left lung has two lobes. The left lung has an underdeveloped third lobe anyway, called the lingula. My embryology and anatomy are dim and distant, so the following conjecture is suspect, but I seem to recall that the heart folds and rotates as it develops in the embryo, as do many other organs in the thorax and abdomen. I further seem to recall that the heart can end up in the right side of the chest every 1 in N births, N being a very large integer. I distinctly remember listening to the heartsounds of a right-sided heart in a patient way back in medical school. (Please note that I did not finish medical school and am thus not an MD. I sampled med school and chose a different path.) -- Chuck McCaffrey cmccaff@urbana.mcd.mot.com 1101 E University Urbana IL 61801 217-384-8585 The opinions are mine. The facts belong to everyone. "If it were done when 'tis done, then't were well it were done bermspicfully."
mikey@bambam.WELLESLEY.EDU (Heather Corbett) (04/07/90)
This has nothing to do with honeycombs. However, it does have to do with DNA. Some resistance genes are on plasmids, which are double-stranded tiny circular chromosomes that occur within E. coli and most likelt other bacteria. Those plasmids can be used in experiments to confer antibiotic resistance on a previously susceptible strain of bacteria. In fact, this is a very useful tool for recombinant work - you put the gene you want on the plasmid, leaving the resistance gene intact. The most widely used plasmid is only about 4.5 kD long, remember; the smaller, the easier it is to get into the cell. Now, if you want to weed out those cells that did NOT take up the gene you wanted to insert, you culture the bacteria on plates with medium containing the antibiotic that the plasmid confers resistance to. Pretty clever, hm? Now, what I am skeptical about is muscle cells taking up mRNA. There is not any good reason that I can think of that a cell would be given a signal to manufacture mRNA for another cell. Eukaryotes (like humans) do not have plasmids, so if anything were transfered it would be mRNA transcripts, but why? Besides, mRNA in the laboratory is extraordinarily fragile and difficult to work with - for one thing, it is single-stranded... very easy to break. If indeed human cells "took up" mRNA for one reason or another, what is the mechanism by which it enters the cell? _In_vitro_ it is very hard to get cells to take up foreign genetic material. Curiously, Heather
baez@x.ucr.edu (john baez) (04/11/90)
In article <12826@bambam.WELLESLEY.EDU> mikey@bambam.UUCP (Heather Corbett) writes: > Now, what I am skeptical about is muscle cells taking up mRNA. There is >not any good reason that I can think of that a cell would be given a signal >to manufacture mRNA for another cell. Well, all I know is that they observed this phenomenon and it was written about in the LA Times; I don't know if they've gotten around to finding a mechanism. Also, there's no good reason for eukaryotes to let in plasmids (or viruses), is there? Let me speculate wildly -- couldn't transfer of mRNA from cell to cell during development facilitate morphogenesis?? I'm a mere mathematician... by the way, I'll be teaching at Wellesley next year --- are you a student, prof...?
riordanmr@clvax1.cl.msu.edu (Patricia McManus) (04/12/90)
In article <12826@bambam.WELLESLEY.EDU>, mikey@bambam.WELLESLEY.EDU (Heather Corbett) writes... > >The most widely used plasmid is >only about 4.5 kD long... Eukaryotes (like humans) do not have >plasmids... I know nothing about muscle and even less about honeycombs, but I do know that nucleic acids (plasmids included) are measured in kilobase pairs (kb) whereas proteins are measured in kilodaltons (kD). Plasmids are rather common in fungi which are eukaryotes, particularily in the mitochondria which are themselves believed to be prokaryotic in nature.