tronvillain

Hey, I'm "a biochem person" too (check my profile). While I see "oxidating" used occasionally, "oxidizing" seems to predominate. I'm assuming there's not some distinction between them that I'm missing.

pepperlandgirl

Thanks for the great responses! I really appreciate them.

Actually, we just learned about this today. But, unfortunately, we couldn't really explore it.
Maybe I've just spent too long round creationists, but they're some of the smartest questions I've seen for a long time! [/quote] Thank you, I try.


Actually, I realize they weren't similar. I worded my question incorrectly. I'm actually not entirely sure what I was thinking. I guess I wanted to know if mitochondria would be considered "living" if they were not part of a eukaryote cell.

This is pretty much what I figured, I just didn't express it quite the same. Thank you.

Like I said before, I'm fascinated by biology, especially evolution. It's realy one of my favorite things to read about and learn about. I've always wanted to be a writer, but now I want to write about evolution. Does that sound crazy?


[quote]

scigirl

<a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=8&t=000008" target="_blank">Not at all!</a>

scigirl

Kosh

[quote]Originally posted by pepperlandgirl:
The class is only <strong>3 weeks long.
</strong>
[/QUOTE

Father Guido Sarducci's 5 minute college???

Beer: "Helping Ugly People Have Sex Since 1865"

Makes it durn hard to select out the cellulose...

lpetrich

I'll take a stab at some of these:

True, it's possible to survive without digesting cellulose; however, cellulose is nevertheless worth digesting if one is able to digest it, because like starch, it is a polymerized sugar. And some animals, like ruminants and termites, are able to live off of cellulose by having microbes in their stomachs digest it for them.

This suggests that, for some reason, it is difficult to evolve cellulose-digestion enzymes; that may explain why ruminants and termites "cheat" and use the services of organisms that have mastered that trick. The whole question of structural constraints on the direction of evolution is a very interesting one, but that question is difficult to answer without a good understanding of the mechanisms for producing various features.

An obvious sort of constraint is a physical constraint, such as being able to obtain enough usable energy to survive or avoiding being too hot or too cold. However, there are other sorts of constraints, such as developmental constraints. Cetaceans are land animals that have gone back to sea, converging on very fishlike shape and habits. However, they still need to surface to breathe air; could it have been too difficult for their ancestors to grow usable gills? But such questions may be difficult to answer without a good understanding of the mechanisms that produce such features.

Finally, methanogens do not digest cellulose; they subsist on the hydrogen released by some of the other bacteria in a cow's stomach.

This is well-established; mitochondria are closest to certain bacteria, like those that live in the root nodules of certain plants. They were "eaten" because they had worked out how to combine food molecules with oxygen for energy, while their hosts had not. Likewise, chloroplasts were once free-living blue-green algae. And this "eating" process can happen more than once, with some protists having extra membranes and the remnants of the nucleus of some other protist that they had "eaten" in this fashion.

Why do plants release oxygen and not nitrogen? One important feature of biological molecules is that they are heavily hydrogenated (reduced, to be precise), and that hydrogen has to come from somewhere. So a plant might either extract hydrogen from ammonia, yielding nitrogen, or extract hydrogen from water, yielding oxygen. Ammonia has the problem of not being as chemically stable as water, so it would be broken down much more easily by heat or solar ultraviolet or lightning. Meaning that a plant would be much better off getting its hydrogen from water than from ammonia. Which is why they release oxygen.

We now consider the merits of nitrogen as opposed to oxygen as a hydrogen sink; which provides the better energy source? Making ammonia does release energy, but the process is relatively difficult; nitrogen fixing is done by that means, but it is only done to produce usable nitrogen compounds. However, making water releases much more energy, and is much easier; which is why oxygen is the favorite hydrogen sink when it is available.

As to releasing carbon dioxide, that is because combining carbon and oxygen to produce it releases energy; biochemical molecule-shuffling processes that release CO2 has that same ultimate result.

abe smith

Pepperland Girl: I too got bit by the Biology bug, back in 1945. I suggest strongly that you MAJOR in Bio, toot sweet; Take every course you can get; read every book you can lay hands on; come on in the water's fine. Blessings on yo' haid! the world needs more people like you. Grandpa. A good way to learn is to read the NOTES in the back of any bio book; those & the bibliographies will lead you on to other sources. Also I suggest you get the habit of reading the NYT TUesday "Science Times" section, to get an idea of what's current; also see the little weekly periodical { at your local library periodical room} "Science News"; wh/ is also available on the Web., i believe. Hey! welcome to *Infidels*! Stick w/ us, Babe! Note that your textbooks, that cost too much! are probably already out-of-date.... xxxxxoo

stryder2112

My research area is in cellulose hydrolysis so I'll take a stab at it. While it's true that cellulose is simply a polymer of glucose like starch, the secondary and tertiary structures are vastly different between the two.

A straight chain of starch contains alpha 1-4 glycosidic bonds between the individual glucose monomers. This causes a secondary structure of the polymer to be a loosely wound helix. If you get a bunch of starch polymers together, these helices can hydrogen bond to one another to form a relatively open tertiary structure that can relatively easily be hydrated and broken up.

On the other hand, cellulose is composed of glucose monomers linked by beta 1-4 glycosidic bonds. The resulting secondary structure is flat and ribbon-like. When you get several of these cellulose chains together, they naturally stack together into a crystalline structure with numerous hydrogen bonds between the adjacent ribbons. This makes cellulose very difficult to hydrate and makes it difficult to "peel" the stacked ribbon-like chains apart. This is what gives cellulose such amazing mechanical strength (e.g. wood).

This difficulty is reflected in the biodegradation of cellulose versus starch. Starch digestion requires two different enzymes. Bacteria and fungi that break down cellulose require a whole system of enzymes (7 or more different enzymes of 3 distinct types) to break down cellulose. In some bacteria these enzymes are packaged into a lipid micelle complex called a cellusome that is responsible for cellulose hydrolysis. Couple this difficulty with the added difficulty of digesting plant cellulose which is encased in another hard-to-break-down aromatic polymer (lignin) and surrounded by yet another carbohydrate polymer (hemicellulose) and you can see how hard it would be to evolve a system for doing this.

Stryder

[ January 24, 2002: Message edited by: stryder2112 ]</p>

BLoggins02

WOW! <img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" />

Just think, I was born 35 years after you got bit by the biology bug. I feel really young now.

Kosh

Your ARE young! 1980? I had just gotten my
first car with a big back se.... uh, what
was your mothers name? Just, uh, wondering.

Quetzal

Hi pepperlandgirl: Welcome to II, and the incredible world of biology and natural history!

If you'd like to learn more than you can find in a Bio 101 class, below are three of my favorite websites. All are very readable, and kind of fun just to explore:

<a href="http://www.sprl.umich.edu/GCL/notes1.html" target="_blank">UMich Global Change Crs</a>, good general discussion of ecosystems, evolution, and origins.

<a href="http://gened.emc.maricopa.edu/Bio/BIO181/BIOBK/BioBookTOC.html" target="_blank">On line biology text</a>, constantly updated.

<a href="http://www.ucmp.berkeley.edu/index.html" target="_blank">UC Berkeley Museum of Paleontology</a>, the entire history of life on earth in a readable, searchable format.

Enjoy!