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mtDNA vs normal DNA - how to illustrate it in plants

Genetics as it applies to evolution, molecular biology, and medical aspects.

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mtDNA vs normal DNA - how to illustrate it in plants

Postby Karen » Sun Jul 10, 2005 6:37 pm

I am one of the editors of a smallorchid magazine and we have just gotten an article submitted about mytochondrial DNA, and I was wondering if there was some "easy" way to illustrate the difference.

I know mithocondrial DNA is found in the organelles and that it supposed is much smaller. Apparently this type of DNA is not found in the pollen of plants, but is only passed on from the mother/seed pod parent. But how and when is it transfered. Is it there from the moment of fertilisation or is it (also) passed on during the maternity periode?

Normal nuclear DNA is spiral shaped, but mtDNA is shaped like circles - right?

I also have read that mtDNA mainly controls characteristics related to the plastids (growth and caroten color), but does it control other things as well?

Really hope to be able to put together i simple diagram showing how it works - preferably so that people who know even less than I do shall be able to understand it w/o going into datails.

Thanks for any help you can provide

btw I found this link - can it meaning fully be translated into plants? (I know the number of chromosomes differs)
http://sunsite.wits.ac.za/focus/h_myto.gif
Regards/ Karen
Karen
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Postby Karen » Sun Jul 10, 2005 7:13 pm

ooops - should I have posted in Molecular Biology?
Regards/ Karen
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Postby ERS » Sun Jul 10, 2005 10:14 pm

Karen,
A little background, then let’s get to the gist of your ‘problem’. In a nutshell, mitochondria contain their own DNA, ribosomes, tRNA and other machinery components for protein synthesis. You are correct, in that mtDNA are in the form of super coiled circular chromosomes (much denser than nuclearDNA). mtDNA is located in specific regions of the mitochondrial matrix called nucleoids. mtDNA replication is independent of nuclear DNA replication. However, the numbers of mitochondria are relatively constant, implying that there must be some cellular regulation on some aspects of organelle replication. With that said, the majority of mitochondrial proteins are encoded by nuclear genes and are then imported from the cytosol. This includes Krebs cycle enzymes. Most proteins encoded by mtDNA are 70s ribosomal proteins and components of the electron transport system. This partial dependence on the nucleus for proteins is why mitochondria are considered semiautonomous organelles. The mitochondrial genome in plants is approximately 200kb pairs which is much larger than most animal mitochondria genomes. As a comparison, human mitochondrial genome is approximately 16kb pairs.

The real meat of mitochondrial inheritance is that cytoplasmic genes do not demonstrate Mendelian patterns of inheritance. Furthermore, it is the cytoplasm of the ovum that transmits the mitochondrial genome. The pollen donation to the effort has no effect because in fertilization, the pollen grain only donates the nuclear package and not the cytoplasmic contents of the sperm cell to the ovum (which contains the food for the embryo etc. via double fertilization). That is a whole other topic though. On an interesting note, extranuclear inheritance is not thwarted by substituting a genetically different nucleus—as in cloning.

As far as illustrating this, I don’t think it would be too difficult please see my Private Message for further recommendations.
ERS
p.s. aren't plants fabulous folks!!!
ERS
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Postby Karen » Mon Jul 11, 2005 6:32 am

ERS, thanks for the reply and yes plants are fantastic - never stops amazing you.

I shall reply later today, thank you so much.
Regards/ Karen
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