essential aminoacids

[Prasad]

why essential aminoacids eventhough essential for the survival is not synthesized in the body?

[insane_alien]

because it takes energy to synthesise them. so as we got plenty of these from food, over time the synthesis pathways got selected out of the species.

[CharonY]

Actually, it is more likely that there was no selective pressure to maintain them.

[Vindhya]

because it takes energy to synthesise them. so as we got plenty of these from food, over time the synthesis pathways got selected out of the species.

 

Then why some amino acids are called semi essential?

[insane_alien]

our bodies can make them, but only under the right conditions and we can't always make enough of them.

 

so if you have the right diet but are lacking semi-essential amino acids, your requirements for those will be lowered, but not completely eliminated.

[jimmydasaint]

Actually, it is more likely that there was no selective pressure to maintain them.

 

Charon Y, I don't quite understand that statement. Would there not be selective pressure to maintain synthesis of essential biochemical components of the diet? It seems counter-intuitive to me at the moment. I would think that an organism capable of essential amino acid synthesis would be able to out compete a rival which cannot do the same, and get a reproductive advantage.

[CharonY]

Not necessarily. If the required element is abundant there will no selective pressure to maintain them. I.e. mutations can occur within this genes without strong negative effects on the organism.

There are scenarios, in which that may be an advantage as flows towards the synthesis of the abundant nutrients could be diverted to something that is more needed. However, synthesis pathways are normally strictly regulated anyway. One would have then to take into account the underlying regulatory networks and the potential effects of disruptions of those by mutations to estimate their impact.

In many cases a neutral assumption comes close to what happens, though.

[Mr Skeptic]

Similar to how many of us have lost the ability to synthesize vitamin C. In the right conditions we get all we need from the diet and so have no need to make our own. Having no need to make our own, there is no mechanism to provide selective pressure to preserve these metabolic pathways.

[jimmydasaint]

OK, so humans evolved to not synthesise the essential amino acids:

 

Arginine

Histidine

Isoleucine

Leucine

Lysine

Methionine

Phenylalanine

Threonine

Tryptophan

Valine

 

However, does the absence of the genes for synthesis of the above comprise an energy-saving mechanism?

 

Additionally, are the genes inactivated by transposable elements?

[insane_alien]

well, yeah, it is energy saving as it takes energy to turn amino acids from one form to another(as well as requiring more input of the base amino acid you're converting.)

[Vindhya]

During the course of evolution if more complex animals are formed (than man), can their requirement of essential amino acids decrease? Can their body adapt itself to produce these essential amino acids?

[insane_alien]

only if there is an advantage to being able to produce the amino acids such as there being significantly lower levels of an essential amino acid in the populations food sources and no suplementary sources are available either.

 

it will of course take many hundreds of generations before the mutation that allows synthesis of the amino acid shows up and takes hold in a significant amount of the populace though.

[CharonY]

Also it depends on how they are inactivated. A simple point mutation, for instance, could happen rather fast, but the complete loss of genes would require probably gene duplication events plus mutations to generate enzymes with similar function. That could take very long (or may not happen at all). Note that this has nothing to do with the complexity of an organism (whatever metric one would use to assess it).