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This micrograph shows two round, membrane-bound organelles inside a cell. The organelles are about 400 microns across and have membranes running through the middle of them.
In this transmission electron micrograph of mitochondria in a mammalian lung cell, the cristae, infoldings of the mitochondrial inner membrane, can be seen in cross-section. (credit: Louise Howard)

Mitochondria divide independently by a process that resembles binary fission in prokaryotes. Specifically, mitochondria are not formed from scratch (de novo) by the eukaryotic cell; they reproduce within it and are distributed with the cytoplasm when a cell divides or two cells fuse. Therefore, although these organelles are highly integrated into the eukaryotic cell, they still reproduce as if they are independent organisms within the cell. However, their reproduction is synchronized with the activity and division of the cell. Mitochondria have their own (usually) circular DNA chromosome that is stabilized by attachments to the inner membrane and carries genes similar to genes expressed by alpha-proteobacteria. Mitochondria also have special ribosomes and transfer RNAs that resemble these components in prokaryotes. These features all support that mitochondria were once free-living prokaryotes.

Mitochondria that carry out aerobic respiration have their own genomes, with genes similar to those in alpha-proteobacteria. However, many of the genes for respiratory proteins are located in the nucleus. When these genes are compared to those of other organisms, they appear to be of alpha-proteobacterial origin. Additionally, in some eukaryotic groups, such genes are found in the mitochondria, whereas in other groups, they are found in the nucleus. This has been interpreted as evidence that genes have been transferred from the endosymbiont chromosome to the host genome. This loss of genes by the endosymbiont is probably one explanation why mitochondria cannot live without a host.

Some living eukaryotes are anaerobic and cannot survive in the presence of too much oxygen. Some appear to lack organelles that could be recognized as mitochondria. In the 1970s to the early 1990s, many biologists suggested that some of these eukaryotes were descended from ancestors whose lineages had diverged from the lineage of mitochondrion-containing eukaryotes before endosymbiosis occurred. However, later findings suggest that reduced organelles are found in most, if not all, anaerobic eukaryotes, and that all eukaryotes appear to carry some genes in their nuclei that are of mitochondrial origin. In addition to the aerobic generation of ATP, mitochondria have several other metabolic functions. One of these functions is to generate clusters of iron and sulfur that are important cofactors of many enzymes. Such functions are often associated with the reduced mitochondrion-derived organelles of anaerobic eukaryotes. Therefore, most biologists accept that the last common ancestor of eukaryotes had mitochondria.


Some groups of eukaryotes are photosynthetic. Their cells contain, in addition to the standard eukaryotic organelles, another kind of organelle called a plastid    . When such cells are carrying out photosynthesis, their plastids are rich in the pigment chlorophyll a and a range of other pigments, called accessory pigments, which are involved in harvesting energy from light. Photosynthetic plastids are called chloroplasts ( [link] ).

Questions & Answers

what is cell?
V.S.Nikhil Reply
The smallest structure and functional unit
Hydra reproduce through which process
Saint Reply
which is smallest organ in our body
pineal gland
Yh in the ears...
why you hand plam is sweating in everytime
who is the father of mycology
Sagar Reply
Heinrich Anton de Bary
describe the similarities and differences between cytokinesis mechanism found in animal cells versus in plant cells
hiro Reply
are humans beings considered to have the eukaryotic cells
success Reply
eukaryotes are organisms that possess cells with a nucleus enclosed in a membrane, humans, and all complex organisms are eukaryotes.
so humans and animals also have cell membranes.... cause I did this test prep and they said plants...I just want to be sure
and thank you for your reply it was helpful👍✌
eu= "perfect", "good", karyon= nut, amound, nucleus
you're welcome. Plants are also eukaryotes.
plants, like animals, possess a nucleus bound by a membrane.
similarities and differences between cytokinesis mechanism found in animal cell vs cell division
Raymark Reply
what is the name of a male flower?
Ikeomu Reply
staminate means flower containing only stamen
what is the definition of evolution in a population?
Homero Reply
the slow changing of a species to adapt to any changes in the environment or how it feeds/hunts. im not good at explaining things lol.
the organ which is sensitive to light in euglena
Fatimah Reply
the organ which is sensitive to light in euglena is
all chlorophyll containing motile cells are sensitive to light
there is no more other chapter
Sandeep Reply
Give tow examples for nutritional deficiency Diseases-
Singampalli Reply
How does a plant cell look like
Sang Reply
in a sleepers form
what do you mean ? I could not understand
they have a regular shape and a large vacoule
I thought it looked like rectangle
a stage in mitosis wherein in spindle fibers begin to shorten to pu the sister chromatids away from each other towards the opposite ends of the cell
Earl Reply
a stage in interphase where chromosome s are duplicated
What is biodiversity
Sp Reply
Name two secretions of Golgi apparatus
Daniel Reply

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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