stein@dhw68k.cts.com (Rick Stein) (12/21/88)
I happen to be watching the "Mac-Neil/Leherer News Hour" on Tuesday
and they had a piece on the Human Genome Project. The background
discussion showed some electron micrographs of the human chromosomes.
I'm curious to know why the DNA material is "stored" in this conformation
as opposed to some other topology. Presumably, there is some "glue protein"
which forces the genetic material into this shape. Does anyone know what
they call this "glue?"
It seems that a great deal of energy is consumed by the cell while the
mitosis process takes place and the "X" and "Y" shapes might be more
energetically efficient if they appeared as "O" or long strands.
Is it true that human genomes only appear in the condensed form just
priori to mitosis and that the genetic material is primary in string
form during the post and pre-mitosis phases of cell life?
Any references to the conformation process would be most helpful.
--
Rick 'Transputer' Stein ( My mother was a clairvoyant. :-) )
uucp:{felix, spsd, zardoz}!dhw68k!stein
Internet: stein@dhw68k.cts.comdd@beta.lanl.gov (Dan Davison) (12/23/88)
In article <17231@dhw68k.cts.com>, stein@dhw68k.cts.com (Rick Stein) writes: > I'm curious to know why the DNA material is "stored" in this conformation > as opposed to some other topology. Presumably, there is some "glue protein" > which forces the genetic material into this shape. Does anyone know what > they call this "glue?" There is a problem in a chapter of the original Lehninger Biochemistry text that will give you the flavor of the problem. Leaving *lots* of other problems aside, the DNA in a human cell if a single straight strand would just about make it to the moon (if I am recalling the problem correctly). In any event, you have at least hundreds of miles of relatively fragile "carbohydrate with nitrogenous contaminants" that you must stuff into a nucleus that is (say) 10e-6 meters in diameter. The "glue" is an assortment of proteins, the predominant ones called "histones" which are among the most highly conserved proteins know. (For example, cow and pea histone (H1?) have one or two differences while their ancestors diverged at least 400 million years ago. -- dan davison/theoretical biology/t-10 ms k710/los alamos national laboratory los alamos, nm 875545/dd@lanl.gov (arpa)/dd@lanl.uucp(new)/..cmcl2!lanl!dd 'The true mark of intelligence is an unwillingness to fill in the many gaps in our understanding with a set of irrational beliefs'(Keats,paraphrased)
werner@aecom.YU.EDU (Craig Werner) (12/29/88)
In article <23046@beta.lanl.gov>, dd@beta.lanl.gov (Dan Davison) writes: > In article <17231@dhw68k.cts.com>, stein@dhw68k.cts.com (Rick Stein) writes: > > I'm curious to know why the DNA material is "stored" in this conformation > > as opposed to some other topology. Presumably, there is some "glue protein" > > which forces the genetic material into this shape. Does anyone know what > > they call this "glue?" > > > There is a problem in a chapter of the original Lehninger Biochemistry > text that will give you the flavor of the problem. Leaving *lots* of > other problems aside, the DNA in a human cell if a single straight > strand would just about make it to the moon (if I am recalling the > problem correctly). The DNA from a single cell can be measured in centimeters. The DNA from a single human being (all told) would probably make it to the moon. You could probably figure it out: 5 * 10^10 nucleotides. Unfortunately I don't have the inter-nucleotide distance handy, but the unit is in Angstroms. . . . . . . . . . . -- Craig Werner (future MD/PhD, 4 years down, 3 to go) werner@aecom.YU.EDU -- Albert Einstein College of Medicine (1935-14E Eastchester Rd., Bronx NY 10461, 212-931-2517) "Until it's on daytime television, it's impossible, and that's the final word."
alexis@reed.UUCP (Alexis Dimitriadis) (12/31/88)
> > There is a problem in a chapter of the original Lehninger Biochemistry > > text that will give you the flavor of the problem. Leaving *lots* of > > other problems aside, the DNA in a human cell if a single straight > > strand would just about make it to the moon (if I am recalling the > > problem correctly). > > The DNA from a single cell can be measured in centimeters. The > DNA from a single human being (all told) would probably make it to the > moon. It's been a few years, but I think it was thus: If you have a strand of silk from here to the moon, how do you pack it in a cylinder X by Y mm? There was a note to the effect that human DNA and the chromosome have the same proportions as the length/width of the strand and the cylinder. This does seems to square with Craig's estimate of a few cm. length for DNA. (I have the book at home, if it's worth the trouble to someone). Alexis Dimitriadis alexis@reed.UUCP (...tektronix!reed!alexis)
pell@boulder.Colorado.EDU (Anthony Pelletier) (01/01/89)
Someone writes: >> > There is a problem in a chapter of the original Lehninger Biochemistry (great book, but a bit out-dated, wouldn't you say?) >> > text that will give you the flavor of the problem. Leaving *lots* of >> > other problems aside, the DNA in a human cell if a single straight >> > strand would just about make it to the moon (if I am recalling the >> > problem correctly). Craig werner writes: >> The DNA from a single cell can be measured in centimeters. The >> DNA from a single human being (all told) would probably make it to the >> moon. In article <11465@reed.UUCP> alexis@reed.UUCP (Alexis Dimitriadis) writes: >It's been a few years, but I think it was thus: If you have a strand of >silk from here to the moon, how do you pack it in a cylinder X by Y mm? >There was a note to the effect that human DNA and the chromosome have the >same proportions as the length/width of the strand and the cylinder. > >This does seems to square with Craig's estimate of a few cm. length for DNA. >(I have the book at home, if it's worth the trouble to someone). > >Alexis Dimitriadis Alexis: God, I hate this...But Craig is quite right (just kidding old boy). Take a typical animal cell (not salamander), it will have about 3x10^^9nucleotides in it That would be about one meter of DNA (which is easily measured in centimeters, I might add). (source :Alberts, Bray, Lewis, Raff, Roberts et al. pp.103, if you don't want to take my word for it). A useful algorithm, for those who like such things: 1micron of DNA= 2kilodaltons = 3 kilobases (If I remember the old 1,2,3 rule correctly--I have to look it up everytime I have to teach it to someone). As for the silk analogy, perhaps they were doing things to scale? That is, if you increased the diameter of DNA to that of silk, the comparable length would reach to the moon? Offhand, this does not sound right either. My guess is you just don't know what you are talking about. Before you make claims like that, you really should check some reputable reference. This sort of discussion is just silly, chromsomes stretching to the moon!!! This is not a place for the unsupported oppinions of those who get all there biology from Nova (and misunderstand it at that). -tony