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MITOCHONDRIA

Discussion of all aspects of biological molecules, biochemical processes and laboratory procedures in the field.

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MITOCHONDRIA

Postby dijitolboy » Mon Jul 18, 2005 1:49 pm

Hey all. Got a question for those of you who know a lot about micro-biology (which seems like ALL of you, judging by the astounding level of acronyms I've encountered that mean nothing to me):

I've been reading about mitochondria, and especially about the fact that they have their own DNA. I've heard all sorts of theories about this, including the one stating that originially, many millions of years ago (perhaps a few billion), that mitochondria would have been a seperate organism that eventually took shelter in our protozoic ancestors. The benefit was obviously mutual. Either way, I'm curious about this DNA. It is totally seperate from human DNA, no? As rediculous as it sounds, I actually was in a bit of an argument with a friend about this. She knows, as do I, that the mitochondria will only come from a mother. However, she seems to think that it's "her DNA", whereas I seem to think that it's neither person's DNA. No matter which parent it came from, it's not human DNA. So there's my question (or questions): is human mitochondria identical to animal mitochondia, and if, through some as-of-yet unaccomplished experiment, the mother's DNA replaced with the father's, wouldn't the organism still turn out the same? Or would there be a genitic conflict (i.e. the cell recognizing the mitochondria as as foreign organism). I've always thought that the mother's DNA was the only passed down because the oocyte contains 99% of the organelles of the soon-to-be zygote. Let me know what you all think; thanks.
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Postby MrMistery » Mon Jul 18, 2005 8:05 pm

You are right in that last sentence of yours. It does contain 99% of the egg cell's organelles. Of course it would differ if you were to put the father'smithocondrial DNA instead of the mother's. DNA is never identical. Mithocondrial DNA of 2 different persons contains info that is common for everyone(info that is needed for protein synthesis) plus info that differes from one person to another, just like human DNA. in your case, i'd say you are right, it's neither person's DNA, it is simply the mithocondrial DNA inherited from the mother.
To sum up, there are some parts of the DNA that are the same for every mithocondria on this planet, but also some that differ from one person to another
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Postby fab » Mon Jul 18, 2005 9:54 pm

I remember the term 'maternal effects' being applied to this situation where the offspring inherits their mother's cytoplasm and mitochondria. This brings up a question of my own. Would maternal effects be considered genetic factors, or environmental factors? To be genetic factors I believe a trait would have to originate from your DNA. But to be an environmental factor it has to have some environmental influence. Would your mother's cytoplasm be considered part of your environment?
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Postby ginny » Mon Jul 18, 2005 11:25 pm

This staff working paper was discussed at the Council's January 2002 meeting. It was prepared by staff solely to aid discussion, and does not represent the official views of the Council or of the United States Government.


The following brief review of some scientific aspects of human and animal cloning is based on scientific research published through the end of December 2001. However, the scientific fields involved in cloning are being very actively investigated, and significant new developments are being published frequently. Publication of new results could change some of the interpretations and emphases in this review.

Use of unfamiliar technical terms and jargon has been avoided wherever possible. Scientific names and terms whose use was required are described and defined in the Glossary of Terms below. In cases where there is disagreement about definitions, this has been noted.

Some Basic Facts about Human Cell Biology and Sexual Reproduction
These elementary facts about human cells, germ cells (egg and sperm), and early embryogenesis will provide the background for understanding the mechanism of cloning and the differences between sexual and asexual reproduction.

Adult human cells with nuclei contain 46 chromosomes, 22 pairs plus two X chromosomes if the adult is female, or 22 pairs plus one X and one Y chromosome if the adult is male. These chromosomes contain the bulk of the cell's DNA, and therefore the genes of the cell. During formation of sperm cells, specialized cell division (meiosis) produces mature sperm cells containing 23 chromosomes (22 chromosomes plus either X or Y). During fertilization of eggs (or oocytes) by sperm, a pronucleus containing half the egg chromosomes is ejected from the cell. Fusion of egg and sperm cells and their nuclei (the defining acts of all sexual reproduction) produces a zygote that again contains a nucleus with the adult cell complement of 46 chromosomes, half from each parent [See Figure 1]. The zygote then begins the gradual process of cell division, growth, and differentiation. After several days in an appropriate nutritive environment, the zygote attains the 100-200-cell (blastocyst) stage. In normal reproduction, the blastocyst implants into the uterine wall, where, suitably nourished, it continues the process of coordinated cell, tissue, and organic differentiation that eventually produce the organized, articulated, and integrated whole that is the new-born infant.

Not quite all the genetic material of a cell resides in its nucleus. Both egg and sperm cells contain small, energy-producing organelles called mitochondria. Mitochondria contain a small piece of DNA that contains the genetic information for making several essential mitochondrial proteins. When additional mitochondria are produced in the cell, the mitochondrial DNA is replicated, and a copy is passed along to the new mitochondria that are formed. During fertilization, sperm mitochondria are selectively tagged and subsequently degraded inside the cell. Thus, the developing embryo inherits solely or principally mitochondria (and mitochondrial DNA) from the egg.

Human reproduction, in cases hampered by one or another cause of infertility, has been accomplished with the help of in vitro fertilization of egg by sperm (IVF) and the subsequent transfer of the early embryo to a woman for gestation and birth. Though such union of egg and sperm requires laboratory assistance and takes place outside of the body, IVF reproduction is still sexual in the biological sense: the new human being arises from two biological parents through the union of egg and sperm.

Egg and sperm cells combined in vitro have also been used to start the processes of animal embryonic development. Implantation of the resulting blastocysts into the uterus of a female of the appropriate animal species is widely used in animal husbandry.

"Reproductive" Cloning (Asexual Reproduction) of Mammals
The startling 1997 announcement that "Dolly" the sheep had been produced by "reproductive" cloning (Wilmut et al, 1997) indicated that it was possible to produce live mammalian offspring via asexual reproduction through cloning with adult donor cell nuclei.1

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Postby Dr.Stein » Tue Jul 19, 2005 1:31 am

Another mitochondria thread? :wink:
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Postby xand_3r » Sat Aug 06, 2005 3:52 pm

As far as I now, mithocondria have their own DNA coding for the oxido-reducing enzymes in the Krebs cycle but they lack the reparatory system of our cells. This means that when we get old we have mithocondria with DNA full of errors - which explains the decrease in the oxido-reducing power. Personally I have a question: are some mithocondria better than others (I know that they are basically the same, but beacause they mutate and mutations canonot be repaired I thought that there are some differences between them) - and I'm thinking also of animal mithocondria. I need to know what animal has mithocondrias with a high rate of enzymes production and a low rate of mutations. I thought that small mammals (rabbits, mice) with intense metabolism must have more mithocondrias or mithocondrias that produce a higher quantity of enzymes.
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