dcohen@paul.rutgers.edu (Dawn Myfanwy Cohen) (05/12/91)
Where do herbivores (especially those like cows that only eat grass)
get amino acids from? Carnivores can obviously get them from meat.
Is it the case that leaves have enough protein for the herbivores,
if eaten in large enough quantities? If so, why couldn't humans
use them as a (possibly incomplete) source of protein, too? Is it
that the herbivores are capable of forming their own amino acids from
products of carbohydrate metabolism? (If so, what is the source of
nitrogen?)
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arpa: dcohen@paul.rutgers.eduwinalski@psw.enet.dec.com (Paul S. Winalski) (05/12/91)
In article <May.11.16.42.41.1991.4952@paul.rutgers.edu>, dcohen@paul.rutgers.edu (Dawn Myfanwy Cohen) writes: |>Where do herbivores (especially those like cows that only eat grass) |>get amino acids from? From the plant material that they eat. |>Is it the case that leaves have enough protein for the herbivores, |>if eaten in large enough quantities? Yes. There's no problem with plant material as a source of protein. Ask any vegetarian. |>If so, why couldn't humans |>use them as a (possibly incomplete) source of protein, too? The problem with most leaves as a source of food is the tough cell walls. Vertibrate digestive tracts can't digest cellulose. Cattle and other herbivores deal with this problem through symbiosis--their digestive tracts are filled with protozoans capable of digesting cellulose. The highly rammified digestive tracts of herbivores are their way of culturing these protozoans and giving them enough time to break down the cell walls of the ingested plant material. Humans can't do this because their digestive tracts aren't set up for it. --PSW
karl@quercus.gsfc.nasa.gov (Karl Anderson) (05/14/91)
In article <1991May11.213947.10968@hollie.rdg.dec.com>, winalski@psw.enet.dec.com (Paul S. Winalski) writes: |> In article <May.11.16.42.41.1991.4952@paul.rutgers.edu>, |> dcohen@paul.rutgers.edu (Dawn Myfanwy Cohen) writes: |> |> |>Where do herbivores (especially those like cows that only eat |> |>grass) get amino acids from? |> |> From the plant material that they eat. |> |> |>Is it the case that leaves have enough protein for the |> herbivores, if eaten in large enough quantities? |> |> Yes. There's no problem with plant material as a source of |> protein. Ask any vegetarian. |> |> |>If so, why couldn't humans use them as a (possibly incomplete) |> |>source of protein, too? |> |> The problem with most leaves as a source of food is the tough |> cell walls. Vertibrate digestive tracts can't digest cellulose. |> Cattle and other herbivores deal with this problem through |> symbiosis--their digestive tracts are filled with protozoans |> capable of digesting cellulose. The highly rammified digestive |> tracts of herbivores are their way of culturing these protozoans |> and giving them enough time to break down the cell walls of the |> ingested plant material. Humans can't do this because their |> digestive tracts aren't set up for it. |> |> --PSW Actually, herbivores are able to manufacture more of the twenty amino acids making up proteins than humans can. In addition, the endosymbionts that play such a large role in ruminant (cows, sheep, deer etc.) digestion can synthesize amino acids using nonprotein nitrogen sources, contributing to the protein intake of their hosts. This is why cows are often fed urea, as a cheap nitrogen source. Human metabolism can synthesize all but seven (the "essential" amino acids) of the twenty; they must get those seven from their food. Few plant foods contain all seven in the proper ratios for humans to be able to utilize them in building proteins. Cereal grains, for example, tend to be low in lysine. There are exceptions, for example soybeans. And it is possible to get the proper ratios by combining plant foods in a meal, for example red beans and rice. Among primates, vegetarian species like gorillas have adaptations to help them extract the maximum possible nutrition from their food. The human vermiform appendix is a vestigial form of an organ that serves our vegetarian relatives as a microbial fermentation vat like the rumen of ruminants. The human appendix lost this function as our progenitors evolved omnivory. -- Karl A. Anderson | Internet: karl@forest.gsfc.nasa.gov NASA/GSFC code 923 (STX) | voice: (301) 286-3815 Greenbelt, MD 20771 | #include "std_disclaimer"
davison@menudo.uh.edu (Dan Davison) (05/16/91)
In article <1991May14.102820@quercus.gsfc.nasa.gov> karl@quercus.gsfc.nasa.gov (Karl Anderson) writes:
Human metabolism can synthesize all but seven (the "essential" amino
acids) of the twenty; they must get those seven from their food.
[..]
Nope, it's nine. The essential: histidine, isoleucine, leucine,
lysine, methionine, phenylalanine, threonine, tryptophan, valine.
The non-essential: alanine, arginine, asparagine, aspartate,
cystenine, glutamate, glutamine, glycine, proline, serice, and
tyrosine.
How did you get 7? I don't see any interconversion pathways in humans
listed...perhaps you were counting salvage pathways?
source: Stryer, "Biochemistry", 3d. ed, pg. 578.
I just finished teaching this a few weeks ago!
dan
--
dr. dan davison/dept. of biochemical and biophysical sciences/univ. of
Houston/4800 Calhoun/Houston,TX 77054-5500/davison@uh.edu/DAVISON@UHOU
Disclaimer: As always, I speak only for myself, and, usually, only to
myself.