pi@hpcuhb.HP.COM (Paul Ilgenfritz) (07/10/90)
I read a book on evolution which left me curious about how organelles in a cell reproduce after a cell divides. In particular, mitochondria, ribosomes, and chloroplasts. Do they divide themselves or are new ones produced under direction from the nucleus? The book implys that they divide since they have their own DNA and RNA but it is never directly stated. The book, _Blueprints:__Solving_the_Mystery_of_Evolution_ (Maitland A. Edey and Donald C. Johanson, Penguin Books), is very good for those who are not experts in the field. It may also be entertaining for the experts since many fascinating anecdotes about the major figures in evolutionary theory are included. (e.g. Darwin dragged his feet on publishing "Origin" until he found out that another guy was about to scoop him.)
eoph12@castle.ed.ac.uk (I F Gow) (07/11/90)
Organelles reproduce in the same way as their ancestral microbes did, i.e. by binary fission. This can be seen on some micrographs as the organelles appearing like "dumb-bell" structures as they are caught dividing. IFG
pi@hpcuhb.HP.COM (Paul Ilgenfritz) (07/12/90)
>Organelles reproduce in the same way as their ancestral microbes did, >i.e. by binary fission. This can be seen on some micrographs as the >organelles appearing like "dumb-bell" structures as they are caught >dividing. Thanks for the confirmation, sorry I was to lazy to go to the library. I can see why analyzing the DNA and RNA of these beasts is such an exciting topic. It seems like it may lead to an understanding of how the first cells evolved.
toms@ncifcrf.gov (Tom Schneider) (07/17/90)
In article <5115@castle.ed.ac.uk> eoph12@castle.ed.ac.uk (I F Gow) writes: >Organelles reproduce in the same way as their ancestral microbes did, >i.e. by binary fission. This can be seen on some micrographs as the >organelles appearing like "dumb-bell" structures as they are caught >dividing. > >IFG Unfortunately this is not a good proof. Mitochondria in serial sections turn out to be all interconnected. It's as if they were one long (perhaps branching) tube. when a slice is made through them, one gets circles and elipses mostly. But a 'dum-bell' is also possible. Consider sections through a banana and you will find these shapes. On the other hand, it does seem reasonable that they would reproduce by fission since they have their own DNA, and this DOES replicate. Since they have an enclosed membrane, it seems that the membrane must also fission. That inference is, of course, not the same as experimental data! Does anyone know more about how they do replicate? Tom Schneider National Cancer Institute Laboratory of Mathematical Biology Frederick, Maryland 21702-1201 toms@ncifcrf.gov
teexmmo@ioe.lon.ac.uk (Matthew Moore) (07/18/90)
In article <5180002@hpcuhb.HP.COM> pi@hpcuhb.HP.COM (Paul Ilgenfritz) writes: > >>Organelles reproduce in the same way as their ancestral microbes did, >>i.e. by binary fission. This can be seen on some micrographs as the >>organelles appearing like "dumb-bell" structures as they are caught >>dividing. > >Thanks for the confirmation, sorry I was to lazy to go to the library. > >I can see why analyzing the DNA and RNA of these beasts is such an >exciting topic. It seems like it may lead to an understanding of how the >first cells evolved. Try following up the name (Lyn?) Margulis. She put forward the view that mitachondria, choroplasts, and the centriole are the descendents of ancient symbionts, which have been an integral part of the evolution of eukaryotes. (mitachondria from bacteria, chloroplasts from blue-greeb algae, which they resemble, and the centriole from spirochaetes).
pi@hpcuhb.HP.COM (Paul Ilgenfritz) (07/18/90)
Here are some emailed responses with names removed to protect the innocent: ---------------------------------------------------- In article <5180001@hpcuhb.HP.COM> you write: > >I read a book on evolution which left me curious about how organelles in a >cell reproduce after a cell divides. In particular, mitochondria, >ribosomes, and chloroplasts. Do they divide themselves or are new ones >produced under direction from the nucleus? The book implys that they >divide since they have their own DNA and RNA but it is never directly >stated. > A brief answer is that the more-or-less autonomous organelles, including mitochondria, plastids, and centrioles, reproduce themselves but coordinate their timing of reproduction with the rest of the cell. Ribosomes are not autonomous, but are produced from DNA templets in either the nucleus or an organelle. A long answer would include discussion of the symbiotic origin of the eukaryotic cell, gradual transfer of genes from the organelles to the nucleus (most dramatic in the contrast between animal mitochondria which have a "stripped down" genome and higher plant mitochondria which retain more of their original genes), and lots of details about the regulation of gene expression, packaging and transport of proteins, export of mRNA's from the nucleus, and regulation of the timing of cell division. The larger organelles consist of a mix of proteins coded by their own genomes and by the cell nucleus. To take chloroplasts as an example, the mix ranges from some algae where almost nothing comes from the nucleus to higher plants where a number of enzymes critical for chloroplast function are coded in the nucleus and produced using nuclear-type ribosomes. A very accessable and visually attractive book, that deals with the varieties of cell structure in different groups, is called _Five Kingdoms_ and is by Lynn Margulis and Karen Schwartz. Most larger libraries should have it, and there is a second edition in print in paperback. -------------------------------------------------------------------- Subject: Re: Organelle Reproduction Newsgroups: sci.bio In-Reply-To: <5180001@hpcuhb.HP.COM> In article <5180001@hpcuhb.HP.COM> you write: > > I read a book on evolution which left me curious about how organelles in a > cell reproduce after a cell divides. In particular, mitochondria, > ribosomes, and chloroplasts. Do they divide themselves or are new ones > produced under direction from the nucleus? The book implys that they > divide since they have their own DNA and RNA but it is never directly > stated. As I recall, chloroplasts divide semi-independently... their own DNA is relativly complete. I've read that the genome of chloroplasts shows a strong relationship to the genome of cyanophytes ("blue-green algae"), and that it's generally believed that chloroplasts evolved from symbiotic cyanophytes. Mitochondria also contain their own DNA... but I believe that it's much less complete than chloroplast DNA, and that mitochondria are dependent on products of nuclear DNA for much of their ability to function. I don't recall how mitochondria reproduce.