Sabtu, 18 Juni 2011


Mitochondria (Gr. mitos, thread, + chondros, granule) are spherical or filamentous organelles 0.5–1 m wide that can attain a length of up to 10 m (Figure 2–11). They tend to accumulate in parts of the cytoplasm at which the utilization of energy is more intense, such as the apical ends of ciliated cells (Figure 17–3), in the middle piece of spermatozoa (Figure 21–10), or at the base of ion-transferring cells (Figure 4–25).

Figure 2-11
Photomicrograph of the stomach inner covering. The large cells show many round and elongated mitochondria in the cytoplasm. The central nuclei are also clearly seen. High magnification.

These organelles transform the chemical energy of the metabolites present in cytoplasm into energy that is easily accessible to the cell. About 50% of this energy is stored as high-energy phosphate bonds in ATP molecules, and the remaining 50% is dissipated as heat used to maintain body temperature. Through the activity of the enzyme ATPase, ATP promptly releases energy when required by the cell to perform any type of work, whether it is osmotic, mechanical, electrical, or chemical.
Mitochondria have a characteristic structure under the electron microscope (Figures 2–12 and 2–13A). They are composed of an outer and an inner mitochondrial membrane; the inner membrane projects folds, termed cristae, into the interior of the mitochondrion. These membranes enclose two compartments. The compartment located between the two membranes is termed the intermembrane space. The inner membrane encloses the other compartment—the intercristae, or matrix, space. Compared with other cell membranes, mitochondrial membranes contain a large number of protein molecules. Most mitochondria have flat, shelflike cristae in their interiors (Figures 2–12 and 2–13A), whereas cells that secrete steroids (eg, adrenal gland; see Chapter 4: Epithelial Tissue) frequently contain tubular cristae (Figure 4–36). The cristae increase the internal surface area of mitochondria and contain enzymes and other components of oxidative phosphorylation and electron transport systems. The adenosine diphosphate (ADP) to ATP phosphorylating system is localized in globular structures connected to the inner membrane by cylindrical stalks (Figure 2–12). The globular structures are a complex of proteins with ATP synthetase activity that, in the presence of ADP plus inorganic phosphate and energy, forms ATP. The chemiosmotic theory suggests that ATP synthesis occurs at the expense of a flow of protons across this globular unit (Figure 2–14).

Figure 2-12
Three-dimensional representation of a mitochondrion with its cristae penetrating the matrix space. Note that two membranes delimiting an intermembrane space form the wall of the mitochondrion. The cristae are covered with globular units that participate in the formation of ATP.
Figure 2-13
Structural lability of mitochondria. A: Electron micrograph of a section of rat pancreas. A mitochondrion with its membranes, cristae (C), and matrix (M) is seen in the center. Numerous flattened cisternae of rough endoplasmic reticulum with ribosomes on their cytoplasmic surfaces are also visible. x50,000. B: Electron micrograph of striated muscle from a patient with mitochondrial myopathy. The mitochondria (arrows) are profoundly modified, showing marked swelling of the matrix.

Figure 2-14
The chemiosmotic theory of mitochondrial energy transduction. Middle: The flux of protons is directed from the matrix to the intermembranous space promoted at the expense of energy derived from the electron transport system in the inner membrane. Left: Half the energy derived from proton reflux produces ATP; the remaining energy produces heat. Right: The protein thermogenin, present in multilocular adipose tissue, forms a shunt for reflux of protons. This reflux, which dissipates energy as heat, does not produce ATP (see Chapter 6: Adipose Tissue).

The number of mitochondria and the number of cristae in each mitochondrion are related to the energetic activity of the cells in which they reside. Thus, cells with a high-energy metabolism (eg, cardiac muscle, cells of some kidney tubules) have abundant mitochondria with a large number of closely packed cristae, whereas cells with a low-energy metabolism have few mitochondria with short cristae.
Between the cristae is an amorphous matrix, rich in protein and containing circular molecules of DNA and the three varieties of RNA. In a great number of cell types, the mitochondrial matrix also exhibits rounded electron-dense granules rich in Ca2+. Although the function of this cation in mitochondria is not completely understood, it may be important in regulating the activity of some mitochondrial enzymes; another functional role is related to the necessity of keeping the cytosolic concentration of Ca2+ low. Mitochondria will pump in Ca2+ when its concentration in the cytosol is high. Enzymes for the citric acid (Krebs) cycle and fatty acid -oxidation are found to reside within the matrix space.
The DNA isolated from the mitochondrial matrix is double stranded and has a circular structure, very similar to that of bacterial chromosomes. These strands are synthesized within the mitochondrion; their duplication is independent of nuclear DNA replication. Mitochondria contain the three types of RNA: ribosomal RNA (rRNA), messenger RNA (mRNA), and transfer RNA (tRNA). Mitochondrial ribosomes are smaller than cytosolic ribosomes and are comparable to bacterial ribosomes. Protein synthesis occurs in mitochondria, but because of the reduced amount of mitochondrial DNA, only a small proportion of the mitochondrial proteins is produced locally. Most are encoded by nuclear DNA and synthesized in polyribosomes located in the cytosol. These proteins have a small amino acid sequence that is a signal for their mitochondrial destination, and they are transported into mitochondria by an energy-requiring mechanism.
The initial degradation of carbohydrates and fats is carried out in the cytoplasmic matrix. The metabolic end product of these extramitochondrial metabolic pathways is acetyl coenzyme A, which then enters mitochondria. Within mitochondria, acetyl coenzyme A combines with oxaloacetate to form citric acid. Within the citric acid cycle, several reactions of decarboxylation produce CO2, and specific reactions catalyzed by dehydrogenase result in the removal of four pairs of H+ ions. The H+ ions ultimately react with oxygen to form H2O. Through the action of cytochromes a, b, and c, coenzyme Q, and cytochrome oxidase, the electron transport system, located in the inner mitochondrial membrane, releases energy that is captured at three points of this system through the formation of ATP from ADP and inorganic phosphate. Under aerobic conditions, the combined activity of extramitochondrial glycolysis and the citric acid cycle as well as the electron transport system gives rise to 36 molecules of ATP per molecule of glucose. This is 18 times the energy obtainable under anaerobic circumstances, when only the glycolytic pathway can be used.
In the process of mitosis, each daughter cell receives approximately half the mitochondria originally present in the parent cell. New mitochondria originate from preexisting mitochondria by growth and subsequent division (fission) of the organelle itself.
The fact that mitochondria have some characteristics in common with bacteria has led to the hypothesis that mitochondria originated from an ancestral aerobic prokaryote that adapted to an endosymbiotic (intracellular symbiosis) life within a eukaryotic host cell.

Medical Application
Several diseases of mitochondrial deficiency have been described, and most of them are characterized by muscular dysfunction. Because of their high-energy metabolism, skeletal muscle fibers are very sensitive to mitochondrial defects. DNA mutations or defects that can occur in the mitochondria or the cell nucleus cause mitocondria diseases. Mitochondrial inheritance is maternal, because few, if any, mitochondria from the sperm nucleus remain in the cytoplasm of the zygote. In the case of nuclear DNA defects, inheritance may be from either parent or both parents. Generally, in these diseases the mitochondria show morphological changes (Figure 2–13B).

Afzelius BA, Eliasson R: Flagellar mutants in man: on the heterogeneity of the immotile-cilia syndrome. J Ultrastruct Res 1979;69:43. [PMID: 501788]
Aridor M, Balch WE: Integration of endoplasmic reticulum signaling in health and disease. Nat Med 1999;5:745. [PMID: 10395318]
Barrit GJ: Communication Within Animal Cells. Oxford University Press, 1992.
Becker WM et al: The World of the Cell, 4th ed. Benjamin/Cummings, 2000.
Bretscher MS: The molecules of the cell membrane. Sci Am 1985;253:100. [PMID: 2416050]
Brinkley BR: Microtubule organizing centers. Annu Rev Cell Biol 1985;1:145. [PMID: 3916316]
Brown MS et al: Recycling receptors: the round-trip itinerary of migrant membrane proteins. Cell 1983;32:663. [PMID: 6299572]
Cooper GM: The Cell: A Molecular Approach. ASM Press/Sinauer Associates, Inc., 1997.
DeDuve C: A Guided Tour of the Living Cell. Freeman, 1984.
DeDuve C: Microbodies in the living cell. Sci Am 1983;248:74.
Dustin P: Microtubules, 2nd ed. Springer-Verlag, 1984.
Farquhar MG: Progress in unraveling pathways of Golgi traffic. Annu Rev Cell Biol 1985;1:447. [PMID: 3916320]
Fawcett D: The Cell, 2nd ed. Saunders, 1981.
Krstíc RV: Ultrastructure of the Mammalian Cell. Springer-Verlag, 1979.
Mitchison TJ, Cramer LP: Actin-based cell motility and cell locomotion. Cell 1996;84:371. [PMID: 8608590]
Osborn M, Weber K: Intermediate filaments: cell-type-specific markers in differentiation and pathology. Cell 1982;31:303. [PMID: 6891619]
Pfeffer SR, Rothman JE: Biosynthetic protein transport and sorting in the endoplasmic reticulum. Annu Rev Biochem 1987;56:829. [PMID: 3304148]
Rothman J: The compartmental organization of the Golgi apparatus. Sci Am 1985;253:74. [PMID: 3929377]
Simons K, Ikonen E: How cells handle cholesterol. Science 2000;290:1721. [PMID: 11099405]
Tzagoloff A: Mitochondria. Plenum, 1982.
Weber K, Osborn M: The molecules of the cell matrix. Sci Am 1985;253:110. [PMID: 4071030]



woww, I wanna save the pict :D


@Ladida simpen aja bos...lumayan buat nakut2in tikus di rumah... XD


It's very trouble-free to find out any matter on web as compared to books, as I found this piece of writing at this web page.

my web blog Evgeni Malkin Authentic Jersey


I do not even know how I ended up here, but I thought this
post was great. I don't know who you are but definitely you are going to a famous blogger if you aren't already ;) Cheers!

my web page; Authentic Sidney Crosby Jersey


Hello! Someone in my Myspace group shared this
website with us so I came to look it over. I'm definitely enjoying the information. I'm
book-marking and will be tweeting this to my followers!
Outstanding blog and wonderful design.

Take a look at my weblog - Abercrombie Fitch Belgique


Wonderful blog! I found it while surfing around on Yahoo News.
Do you have any suggestions on how to get listed in Yahoo News?
I've been trying for a while but I never seem to get there! Thank you

my homepage - Louis Vuitton Handbags


Asking questions are genuinely good thing if you are not understanding anything
fully, but this post offers good understanding yet.

My webpage: Gucci Borse


I get pleasure from, result in I found just what I used to be looking for.
You have ended my 4 day lengthy hunt! God Bless you man. Have a nice day.

Feel free to visit my site: an Seo software evolution


I really like your blog.. very nice colors & theme.
Did you design this website yourself or did you hire someone to do it
for you? Plz reply as I'm looking to construct my own blog and would like to find out where u got this from. thank you

My weblog


Wonderful web site. A lot of helpful information here.
I'm sending it to some pals ans also sharing in delicious. And of course, thanks in your effort!

Here is my web blog:


I know this if off topic but I'm looking into starting my own blog and was wondering what all is needed to get setup? I'm assuming
having a blog like yours would cost a pretty penny?
I'm not very internet savvy so I'm not 100% certain. Any suggestions or
advice would be greatly appreciated. Appreciate it

Look at my webpage; Abercrombie Et Fitch


Greetings! Very helpful advice in this particular post! It
is the little changes that make the largest changes.
Thanks for sharing!

my web-site: relic watches for men


When someone writes an post he/she retains the
idea of a user in his/her brain that how a user can understand
it. Thus that's why this post is perfect. Thanks!

Here is my blog post :: strength shoes workout


Nice weblog here! Additionally your website lots up very fast!
What host are you the usage of? Can I am getting your
associate link to your host? I want my site loaded up as quickly as yours lol

Feel free to surf to my blog post ... Abercrombie and Fitch


great publish, very informative. I'm wondering why the other specialists of this sector don't notice this.
You must proceed your writing. I'm sure, you have a huge readers' base

Have a look at my webpage: Louis Vuitton Outlet


What's up, I want to subscribe for this website to obtain newest updates, thus where can i do it please assist.

my weblog: Nike Air Jordan


Hey there! I just wanted to ask if you ever have any issues with hackers?
My last blog (wordpress) was hacked and I ended up losing several weeks of hard
work due to no back up. Do you have any solutions
to prevent hackers?

Also visit my blog: Clicking Here


Great post.

My blog - NFL Jerseys Cheap


Hi Dear, are you truly visiting this web page regularly, if so after that you will
without doubt get nice experience.

Visit my web page: Jordan Femme


Hi there I am so thrilled I found your web site, I
really found you by mistake, while I was browsing on
Google for something else, Anyways I am here now and would just like to say thanks a
lot for a marvelous post and a all round enjoyable blog
(I also love the theme/design), I don’t have time to read it all
at the minute but I have bookmarked it and also added your RSS feeds, so when I have time I will
be back to read a great deal more, Please do keep up the fantastic work.

my webpage; Chaussure De Foot


My family members all the time say that I am wasting
my time here at net, except I know I am getting knowledge all
the time by reading thes fastidious posts.

My web-site


Great post. I used to be checking continuously
this blog and I am impressed! Very useful information specifically the final section :) I
deal with such info much. I used to be seeking this particular info for a long time.
Thanks and good luck.

my blog; Christian Louboutin


Thanks for sharing your thoughts. I really appreciate your efforts and I
am waiting for your further post thanks once again.

Look into my web site; helpful resources


I've been exploring for a little bit for any high quality articles or blog posts in this sort of space . Exploring in Yahoo I ultimately stumbled upon this website. Reading this info So i'm glad to express
that I have an incredibly good uncanny feeling I found out just what I needed.
I such a lot certainly will make sure to don?t overlook this web site and provides it a
glance on a constant basis.

Here is my webpage; Michael Kors Bags


Hey there! I've been reading your site for some time now and finally got the bravery to go ahead and give you a shout out from Houston Texas! Just wanted to tell you keep up the fantastic work!

my web-site: Air Max Femme


Hi there mates, its great post about teachingand fully explained, keep
it up all the time.

Feel free to surf to my site ... Nike Air Max


I do not know if it's just me or if everybody else encountering issues with your site. It seems like some of the text in your content are running off the screen. Can somebody else please provide feedback and let me know if this is happening to them too? This could be a problem with my web browser because I've had this happen previously.

Stop by my webpage - Oakley Sunglasses


May I simply just say what a relief to discover somebody who actually knows what they are talking about on the
web. You actually understand how to bring an issue
to light and make it important. More and more people need to check this out
and understand this side of the story. I can't believe you aren't more popular
given that you definitely possess the gift.

Here is my web-site :: Chaussures De Foot - -


I savor, result in I discovered just what I used
to be taking a look for. You have ended my 4 day long hunt!
God Bless you man. Have a great day. Bye

Feel free to visit my web-site: Sac A Main Louis Vuitton


I am regular reader, how are you everybody? This post posted at this website is actually good.

Feel free to surf to my blog :: helpful resources


I have been surfing on-line more than 3 hours these days, yet I never discovered any interesting
article like yours. It's lovely value sufficient for me. In my view, if all site owners and bloggers made excellent content as you probably did, the net will probably be much more helpful than ever before.

Here is my blog post Louis Vuitton Bags []


I'm really enjoying the theme/design of your weblog. Do you ever run into any browser compatibility problems? A small number of my blog audience have complained about my website not operating correctly in Explorer but looks great in Opera. Do you have any recommendations to help fix this issue?

Here is my homepage: Read More

Posting Komentar

Posting Lebih Baru Posting Lama Beranda


Chat Box

Top Commentators

Give Me +1


Foto Saya
I created this blog just to support the activities of my learning about histology and others



Copyright © 2011 De Histology

Templates by Poncol Gate | CSS3 by David Walsh | Powered by {N}Code & Blogger