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  #1  
Old 04-16-2010, 11:34 AM
kanicbird kanicbird is offline
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Where does protein (& amino acids) come from?

For the purpose of this, I'm just taking amino acids and protein interchangeably as one is just a combo of the other.

Plants have some protein but are they the only source? Do animals just concentrate them and rearrange them, or do animals actually make protein out of non-protein (non-amino acids)?
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  #2  
Old 04-16-2010, 11:37 AM
Shmendrik Shmendrik is offline
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Quote:
Originally Posted by kanicbird View Post
For the purpose of this, I'm just taking amino acids and protein interchangeably as one is just a combo of the other.

Plants have some protein but are they the only source? Do animals just concentrate them and rearrange them, or do animals actually make protein out of non-protein (non-amino acids)?
Some amino acids are "essential", which means the human body can't synthesize them, so they are an essential part of the diet. But most amino acids can be synthesized from non-AA precursors.
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Old 04-16-2010, 11:42 AM
Triskadecamus Triskadecamus is offline
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Actually, plants have proteins in them too, and amino-acids. So do a number of types of less complex forms, including yeasts (fungi) and bacteria, even viruses.

Humans manufacture their own proteins, with the exceptions already noted, and when they ingest proteins almost all of those proteins are broken down and converted into others things before they are used.

Tris
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  #4  
Old 04-16-2010, 11:47 AM
Markxxx Markxxx is offline
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Think of it like this, different animals need different proteins and in differing amounts. This is akin to different animals need different vitamins and in differing amounts.

This is why humans have to eat different plant foods to get a complete protein. (Or eat animal products). But the protein needs for a human is different from a cat or a dog.
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  #5  
Old 04-16-2010, 12:26 PM
Smeghead Smeghead is offline
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Ultimately, all the carbon comes from photosynthesis, and the nitrogen comes from nitrogen-fixing bacteria. But yes, your body is making and breaking down both proteins and amino acids all the time.
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  #6  
Old 04-16-2010, 12:30 PM
Crescend Crescend is offline
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Oversimplified summary: A protein is a chain of amino acids. A given organism will usually have some amino acids that they can synthesize from other chemicals (non-essential) and some that they cannot, which means that they need to ingest them (essential). There's 20 'standard' amino acids in nature, of which different ones are essential and non-essential for different organisms. Assuming you have the needed amino acids, a protein is made by putting them in a chain. Ingested protein is broken down into single amino acids before we can use those amino acids as building blocks for our proteins.

There are different types of "non-essential" amino acids, by the way. Some can be made from very generic material, while others can only be made from other, essential amino acids. It depends on what machinery you have.
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  #7  
Old 04-16-2010, 12:33 PM
ToeJam ToeJam is offline
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Also the sequence is:
Amino Acid---> Peptide ---->(Complex) Polypetides--->> Proteins. Proteins are made up of peptides which are then made up of the Amino acids. So when you tend to eat nutrients, they fall into 3 categories: Lipids, Sugars, and proteins (broken down into their amino acid forms).

Sugars can be used via the TCA cycle to produce energy, and a few of the byproducts of the cycle is that a few amino acids are produced naturally from the sugar molecules. We can use those, and then convert those molecules to further make other amino acids and peptides as needed. However, there are a few amino acids that we cannot produce naturally, and as mentioned above we must seek them out in our diet to compensate.
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  #8  
Old 04-16-2010, 12:34 PM
lazybratsche lazybratsche is offline
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There are 20 different amino acids, and all living things need at least a trace amount of every one (though there are some organisms that can substitute one particular amino acid for another in certain circumstances). Plants and microbes can synthesize all of the amino acids they need*, as long as they've carbon and nitrogen sources. Herbivores, similarly, can synthesize the amino acids they need, though sometimes they depend on gut bacteria for particular amino acids.

Over the course of evolution, omnivores and carnivores that can get the necessary amino acids in their diet have lost the ability to synthesize certain amino acids. Humans, in particular, can no longer synthesize eight of them, and we must get these amino acids in our diet. These are the "essential" amino acids, and we need significant quantities of these from the food we eat. A small amount of meat, or the right combination of high-protein vegetables and grains, will provide the essential amino acids in our diet. For a given amino acid, if we eat too little we'll die, a bit more we'll survive but be unhealthy, and there's some optimal amount where we'll be healthy. And if we get too much overall protein (greater than 30% of our total caloric intake), our kidneys can't handle the toxic metabolic by-products of burning protein for energy.



*in biology there are always exceptions... someone will be along shortly with a correction.
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  #9  
Old 04-16-2010, 12:46 PM
lazybratsche lazybratsche is offline
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Originally Posted by Triskadecamus View Post
Actually, plants have proteins in them too, and amino-acids. So do a number of types of less complex forms, including yeasts (fungi) and bacteria, even viruses.
Every living thing has protein. And every plant has every amino acid in some quantity, it's just that most plants have only trace amounts of certain amino acids. Thus, we need to find plants with high levels of the essential amino acids to get enough of all the essential amino acids.

To get a little more specific, the essential amino acids in humans are phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine, and lysine. Corn is a relatively good protein source, but it doesn't have enough lysine or tryptophan, so we can't eat corn alone. Beans, likewise, are also protein-rich, but they lack methionine. So a diet based on both corn and beans provides all of the amino acids we need to grow and to be healthy.

Last edited by lazybratsche; 04-16-2010 at 12:46 PM..
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  #10  
Old 04-16-2010, 01:10 PM
kanicbird kanicbird is offline
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Do animals make amino acids from just other amino acids or can they use non amino acids as the building blocks and manufacture amino acids? One person stated that breakdown of sugar will produce some amino acids though that production is unclear if it's new, or just a reused amino acid that is remade into a different amino acids.

But besides that it seems like the answer is unclear if animals actually manufacture amino acids from raw materials, as opposed to just reorganizing amino acids from other amino acids, in which case all amino acids would come from plants, and just processed by animals.
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  #11  
Old 04-16-2010, 01:19 PM
Shmendrik Shmendrik is offline
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Quote:
Originally Posted by kanicbird View Post
Do animals make amino acids from just other amino acids or can they use non amino acids as the building blocks and manufacture amino acids? One person stated that breakdown of sugar will produce some amino acids though that production is unclear if it's new, or just a reused amino acid that is remade into a different amino acids.

But besides that it seems like the answer is unclear if animals actually manufacture amino acids from raw materials, as opposed to just reorganizing amino acids from other amino acids, in which case all amino acids would come from plants, and just processed by animals.
Animals manufacture amino acids from non-amino acid precursors, including sugars, as noted above. However, ammonia is needed for this process because sugars have no nitrogen, and most ammonia ultimately comes from protein, in the western diet.

I don't understand what you mean by "reorganizing amino" acids, and "processed by animals". If every atom of the amino acid molecule were disassembled and used to make new amino acids, and in the interim they are part of other macromolecules, would you describe that as processing? Reorganization?
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  #12  
Old 04-16-2010, 01:26 PM
kanicbird kanicbird is offline
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Originally Posted by Shmendrik View Post
Animals manufacture amino acids from non-amino acid precursors, including sugars, as noted above. However, ammonia is needed for this process because sugars have no nitrogen, and most ammonia ultimately comes from protein, in the western diet.

I don't understand what you mean by "reorganizing amino" acids, and "processed by animals". If every atom of the amino acid molecule were disassembled and used to make new amino acids, and in the interim they are part of other macromolecules, would you describe that as processing? Reorganization?


It would seem like materials input yield materials output
or to write it differently:
Input > Output
Can animals get amino acids on the output side without putting any amino acids in on the input side?
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  #13  
Old 04-16-2010, 01:36 PM
Shmendrik Shmendrik is offline
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Originally Posted by kanicbird View Post
It would seem like materials input yield materials output
or to write it differently:
Input > Output
Can animals get amino acids on the output side without putting any amino acids in on the input side?
Yes. Some of the nitrogen comes from other sources, such as nucleotides, so it's likely that some of the amino acids made by the body do not derive any of their substituent atoms from amino acids.
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  #14  
Old 04-16-2010, 03:29 PM
Smeghead Smeghead is offline
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It's really very simple
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  #15  
Old 04-16-2010, 03:38 PM
Shmendrik Shmendrik is offline
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Originally Posted by Smeghead View Post
Unfortunately, if I understand the OP correctly, it's not that simple, since you have to know what else goes in during some of those reactions, and where that comes from. But that is the gist of it. I'd recommend chapters 19 and 20 of Lippincott's Biochemistry.
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  #16  
Old 04-16-2010, 04:10 PM
lazybratsche lazybratsche is offline
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Originally Posted by Shmendrik View Post
Animals manufacture amino acids from non-amino acid precursors, including sugars, as noted above. However, ammonia is needed for this process because sugars have no nitrogen, and most ammonia ultimately comes from protein, in the western diet.
I think animals (humans, herbivores, or otherwise) depend on ingested proteins for the vast majority of their nitrogen intake. These proteins ultimately come from plants or microbes, which can use nitrates, ammonia, etc. as a nitrogen source. Nitrogen isn't an abundant component of nucleotides, and they make up a pretty small fraction of your food.

I know that some herbivores (cows in particular) can use a modest amount of ammonia or urea in their diet as a nitrogen source, but they rely on gut bacteria to convert these into amino acids.

So for humans, I'd say that pretty much all the amino acids we synthesize use nitrogen from other amino acids. Of course, that's not very surprising. Biochemically, it's relatively easy to remove or add side chains to an existing amino acid, and most of these side chains lack nitrogen.
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  #17  
Old 04-16-2010, 05:29 PM
Triskadecamus Triskadecamus is offline
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Originally Posted by lazybratsche View Post
Every living thing has protein.
Well, I didn't make that clear, although I did say that plants, fungi, bacteria, and viruses (which either are, or are not alive, depending on which biological church you attend) do. I did leave out the Archea, and some others.

Yeah, Protein is part of all living things.

Tris
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