how essential amino acids are synthesised

[krompir2]

Hello!

We've all heard of essential amino acids, which can not be synthesised in our own body. My question is, why can't we do that and also how come are animals capable of synthesising them?

I appreciate all of your answers.

[CharonY]

We (as other animals) basically lost the ability to synthesize a number of amino acids, presumably because there was no selective pressure to maintain the required genes (and hence, metabolic pathways).Thus it is not that we are any kind special in that regard, as other animals also lack the ability to synthesize all amino acids.

[krompir2]

I see. But how do they get in our food? What biochemical reactinos are responsible for that?

[CharonY]

Proximately you can get them from organisms that either synthesized them or obtained them from other organisms. Ultimately there are a number of plants and bacteria that synthesize them (and also certain animals). The synthesis pathways are dependent on the specific amino acid in question.

 

If you eat meat, for example they will contain proteins that include essential amino acids that the animal may have obtained from various plant or animal sources, for example. Instead of synthesizing the respectiva amino acid our body degrades the protein to its constituents (i.e. the amino acids).

Edited November 14, 2012 by CharonY

[Jens]

CharonY has answered your questions.

In case you are interested in more details, why exactly these amino acids, here some additional thoughts:

 

Facts:

- The published list of essential amino acids is Val, Ile, Leu, Thr, Lys, Met, Phe, Trp, His. This means that humans cannot synthesize them. The other 11 amino acids can be synthesized.

- There is no amino acid storage in the human body (besides usage in proteins).

- All proteins usually contain all amino acids. Only Trp makes up about 1% of the used amino acids. So in nearly 100% of all proteins you find at least 19 different amino acids. This means if you do not eat proteins, your body need to degrade other proteins to synthesize any protein.

 

Question: What is the sense of beeing able to synthesize 11 amino acids, if you cannot synthesize a single protein with this capability?

 

Answer: Actually for 9 of the 11 other amino acids the human body just is able to synthesize them by pure chance, because the enzymes for this are needed for other purposes any way. The only exceptions are Pro (proline) and Asn (asparagine).

 

Question: Why is it important for the human body to synthesize Pro (proline)?

Most proteins have a roughly standard distribution of the usage of the amino acids. This means if you eat proteins from plants they are very well suited to reconstruct human proteins out of the amino acids. But there is one big exception: collagen is quantitatively the most important protein in animals. Collagen has a very special amino acid composition. Pro and Gly are highly over-represented, because they are needed to form the quite unique secondary structure of collagene. So the synthesis of Pro is crucial for survival, if you eat only plant proteins (they do not have collagen).

 

Question: Why is it important for the human body to synthesize Asn (asparagine)?

No idea yet.

 

Summary: Actually it makes no sense to learn the essential amino acids by heart. With the exception of proline they are essential by pure chance, because the enzymes for there synthesis are not needed in any other pathways.

 

I hope this provides more insight. Jens

 

 

[BabcockHall]

In general the nonesssential amino acids are produced by transaminations of glycolytic or TCA cycle intermediates, or a few extra reactions. The essential amino acids generally have longer pathways. The aspartate pathway and the aromatic amino acid pathway both have many steps.

[Vignesh Loganathan]

In general the nonesssential amino acids are produced by transaminations of glycolytic or TCA cycle intermediates, or a few extra reactions. The essential amino acids generally have longer pathways. The aspartate pathway and the aromatic amino acid pathway both have many steps.

then you mean that those longer pathway for synthesis of essential aminoacids are present in other organisms other than us?

[CharonY]

Yes, most animals have reduced anabolic amino acid pathways. Apparently there was no selective pressure to maintain the respective genes and subsequently we lost the ability to synthesize them.

[alpha2cen]

Is this essential amino acid the vestige of metabolic evolution in human as a result of environmental change and human adaptation?

From the knowledge of the essential amino acid, can we learn what our ancestors ate at that era ?

Edited January 29, 2013 by alpha2cen

[vampares]

 

n the group of amino acids that cannot be synthesized by the organism but are required by the organism.

 

The "essential" amino acid concept is a bit skewed.

 

Humans cannot produce their own amino acids. From the ecological standpoint amino acids are essential.

 

Humans use all the amino acids. Amino acid sources are not ordinarily found incomplete or in isolated form. Where one is found, every other one will be found, albeit in minute quantities in some instances.

 

There are no instances that I know of where the "essential" amino acids are found isolated from all other amino acids.

 

If you ate just those amino acids your diet would be way off. The lack of glutamine, the phenylalinine intolerance, the homocystine, forget serine, alinine and glycine! It would have you reeling. Your children's urine would be toxic!

 

 

On the other side in the biosynthesis of the "other" amino's, the methylation provided by methionine is an essential process.

Edited February 2, 2013 by vampares

[Consistency]

We (as other animals) basically lost the ability to synthesize a number of amino acids, presumably because there was no selective pressure to maintain the required genes (and hence, metabolic pathways).Thus it is not that we are any kind special in that regard, as other animals also lack the ability to synthesize all amino acids.

 

You have no EVIDENCE which says we LOST THE ABILITY to produce the essential amino acids. Its bolony. Stop spreading unscientific information.

 

Only plants and bacteria have the enzymes, and have always only had them.

 

If we had the enzymes to produce our own essential amino acids, we wouldn't need to eat, we wouldn't need a mouth, we could stand under the sun and do photosynthesis like plants. But we can't.

 

Animals(like us) don't lack the ability to synthesize all the amino acids. Animals(like us) lack the ability to synthesize the essential amino acids.

 

Animals(like us) can synthesize the non-essential amino acids from essential amino acids.

Edited February 5, 2013 by Consistency