Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: quadir on 31/12/2002 11:55:56
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i have got an assignment which requires information
about how cells mutate and why and how these
mutations occur. any help would be welcomed!
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Thanks for your enquiry.
Cells themselves don't mutate; rather their DNA, which dictates how cells behave, is altered, leading to a change in cell function, one consequence of which includes cancer :
http://www.thenakedscientists.com/HTML/Guestfile/helenaearl.htm
There are many ways to introduce changes into DNA, either intentionally, as used by scientists, or unintentionally, as occurs in nature.
http://www.thenakedscientists.com/forum/index.php?topic=35
Scientists change DNA sequences by selectively adding and removing pieces of DNA to study the effect on individual cells in a dish, or even on an entire animal as in a transgenic mouse.
See Kat Arney's column for more information on genetically modified mice :
http://www.thenakedscientists.com/HTML/articles/article/katarneycolumn2.htm
...and Mark Tester's column about GM plants:
http://www.thenakedscientists.com/HTML/articles/article/marktestercolumn.htm
There are many ways in which DNA can be mutated by things present in the environment. For example radiation, including Xrays, Gamma Rays, UV light:
http://www.thenakedscientists.com/HTML/articles/article/bobburycolumn3.htm
...and the carcinogens present in cigarette smoke.
These agents interact with DNA, in one way or another, to alter the genetic sequence, distorting the instructions given to the cell. The changes within the DNA can be gross - rearrangements of whole portions of chromosomes for example, or restricted to a single DNA base or letter.
Every cell in the body contains a complete copy of your DNA, and when that cell divides, to replace dead cells, or to help you grow, it has to make a copy of your entire DNA sequence - one copy for each of the 2 new daughter cells.
http://www.thenakedscientists.com/HTML/articles/article/chrissmithcolumn.htm
In order to generate a new copy of your DNA an enzyme, DNA Polymerase is used. It usually makes a faithful copy of your DNA sequence, partly because it has the ability to check for errors as it makes the copy. But all systems are fallable, and occasionally it makes a mistake, changing an occasional letter in your DNA sequence. Most of these mistakes never cause a problem because the majority of your DNA doesn't code for anything so changes within the non-coding regions don't have a major impact. Also, because in some instances you can change the genetic code and the protein product remains the same (so called degeneracy), even mutations within the coding regions are not necessarily clinically manifest.
This is a very simple overview, but hopefully it will help you get started.
TNS
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I'm sure you know this naked (and good overview by the way, I'm sure that helped quadir out a lot) but I want to bring up on key point for others who might read this that you left out, and frankly a lot of people leave out of the story. Cells don't even have to have a change in their DNA to induce a change in their function. Environmental factors (whether from sources outside the body, put into the body, or chemicals excreted by neighboring cells). Remember that all your cells have an IDENTICAL copy of your DNA. They obviously do not all express everything that is encoded into that DNA though. If they did, and you had blue eyes, the fat cells in your butt would excrete the same blue pigments found in your eyes, and you'd have a blue butt too. As a matter of fact every cell in your body would be identical. So ontop of the actual genes encoded in your DNA there are also many elements that regulate which of these codes will be read (transcription factors). These factors can be influenced dirrectly by external cues, and can thus change the activity of a cell with no actual change in DNA.
Like I said before, I know that this doesn't dirrectly relate to the actual question (but its a neat side point) and most people on this site already know about it. But we get so worked up about the genes coded in our DNA that we over look TF's quite often so its good to remind ourselves about them
Yar, the flies be everywhere!!!
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A reasonable point, but as you say yourself, the question specifically asked about DNA mutation, not how genes alter their function due to external factors. In the context of cancer this would be more consistent with a 'paraneoplastic' effect.
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who says cells can't change their DNA? adaptive mutation in
bacteria says they can.
all you need to do is look at the fruit fly used in research
to see that there is far more involved than random mutation
of genes
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no one said (at least not specifically in those words) that cells cannot change their DNA. Just that mutation in cells is caused my changes in DNA. HOwever, the fact of whether a cell can change its DNA is a matter of whether you believe that cells control DNA, or DNA controls cells. There is a very interesting book called "the smart gene" that proposes the theory that DNA is the true life form of this universe, and that it just "builds" our bodies and vessels by which to purpetuate itself. There are other people who go by similar theories but see DNA more along the lines of a parasite rather than a....whatever you would call what I explained in the last sentence.
I have seen some of the studies that you refer to in bacteria. Although it is not very comon in other kingdoms to my knowledge.
I am VERY currious as to which drosophila (fruit fly) studies you are refering to. Could you give me a few examples?
This is a signature.... AND YOU WILL LIKE IT!!
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who says cells can't change their DNA? adaptive mutation in
bacteria says they can.
all you need to do is look at the fruit fly used in research
to see that there is far more involved than random mutation
of genes
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no one said (at least not specifically in those words) that cells cannot change their DNA. Just that mutation in cells is caused my changes in DNA. HOwever, the fact of whether a cell can change its DNA is a matter of whether you believe that cells control DNA, or DNA controls cells. There is a very interesting book called "the smart gene" that proposes the theory that DNA is the true life form of this universe, and that it just "builds" our bodies and vessels by which to purpetuate itself. There are other people who go by similar theories but see DNA more along the lines of a parasite rather than a....whatever you would call what I explained in the last sentence.
I have seen some of the studies that you refer to in bacteria. Although it is not very comon in other kingdoms to my knowledge.
I am VERY currious as to which drosophila (fruit fly) studies you are refering to. Could you give me a few examples?
This is a signature.... AND YOU WILL LIKE IT!!
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I thought ALL mutations were random. Am i wrong? If I am right, you cannot possibly say that cells "control" DNA? Cells may be able to control what genes are expressed, but i thought that since mutations are random, it's just like saying we control the throw of a die.
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And let`s not forget about phisiologycal roll of mutations. Although, very rare, they occur in, for instance, activated B limphocytes, in process called somatic hypermutation which is responsible for production of antybodies of very high affinity for antigen. Also, in this process, the mutations are random, but cells with mutations that facilitates binding of foreign antigen are induced to devide more and more, and those which are not capable to produce "good" antybodies capable to effectievly bind antigen dies by apoptosis.
In a way, this is a case in which cell (organism) induce mutations in cells, and selects those ones that are good in a content of a function.
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quote:
Originally posted by alastair84
I thought ALL mutations were random. Am i wrong? If I am right, you cannot possibly say that cells "control" DNA? Cells may be able to control what genes are expressed, but i thought that since mutations are random, it's just like saying we control the throw of a die.
a mutation by definition is not neccisarily random. it just means a change in code. If I purposely changed a T to a G thats would still be a mutation, but it cn not be considered random. HOwvere, getting to the point that you were talking about, most mutations in nature are random (at least to some degree... a point mutation is more random than a translocation etc.) and they DO happen randomly. But the don't have to HAPPEN randomly. Many bacteria and other cells possess the ability to cause conditions withinthemselves that favor mutations often while under some sort of stress. the hope being that they will by chance mutate to a form that is better fitted to the current conditions. So while the actual mutation in that case is random, the fact that it happened isn't. To use your example, while I can't control what the dice land on, I can control whether or not I throw them. Although from time to time I may drop them even when I mean to hang on to them. Also in refference to different types of mutations, I can throw a 6 sided die or a96 sided die. odds are a little different
That's no moon.... its a GRAPEFRUIT!!!!
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Beautifully argued.
For interest's sake, can you provide some examples of this pro-mutational state occurring - i.e. some organisms in which it is known to happen, and the biochemical basis for how it is achieved.
Cheers,
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Awe, geeze you're calling my bluff eh? :)
Its been about 4 years since micro, and 2 since molecular, but I remember learning about these phenomena in both (especially micro) If work ever clams down (so never) I'll dry to dig out the old info for ya
That's no moon.... its a GRAPEFRUIT!!!!