How are non essential amino acids synthesized?

[sameeralord]

Hello everyone,

My biochemistry book just says there are 20 amino acids that are essential and not synthesizd by the body. Then it doesn't say how other amino acids are synthesized. My guess is they are synthesized from transamination reactions of essential amino acids. Does that mean if you don't get 20 essential amino acids you would not have the rest either. Thanks

 

[Ygggdrasil]

There are 20 amino acids that are commonly used as building blocks for proteins. Of those 20, eight are not synthesized by the body and are considered essential. Many of the other non-essential amino acids are synthesized from intermediates of the central metabolic pathways (the reactions to synthesize the amino acids do generally involve a transamination step). For example, 3-phosphoglycerate, an intermediate in glycolysis, can be converted into serine, and serine can be converted into glycine.

Because most of these non-essential amino acids are not synthesized from essential amino acids (there are some exceptions like cysteine, however), a deficiency in essential amino acids should not impair synthesis of the non-essential amino acids (unless it gets so severe that there aren't enough essential amino acids to synthesize the enzymes needed to create the non-essential amino acids).

 

[sameeralord]

There are 20 amino acids that are commonly used as building blocks for proteins. Of those 20, eight are not synthesized by the body and are considered essential. Many of the other non-essential amino acids are synthesized from intermediates of the central metabolic pathways (the reactions to synthesize the amino acids do generally involve a transamination step). For example, 3-phosphoglycerate, an intermediate in glycolysis, can be converted into serine, and serine can be converted into glycine.

Because most of these non-essential amino acids are not synthesized from essential amino acids (there are some exceptions like cysteine, however), a deficiency in essential amino acids should not impair synthesis of the non-essential amino acids (unless it gets so severe that there aren't enough essential amino acids to synthesize the enzymes needed to create the non-essential amino acids).

Thanks a lot for the nice precise answer Ygggdrasil I really did make a meal out of the numbers. I checked the homocysteine cycle and how it forms cysteine after reading your reply. My problem is that for transamination reactions you already need an amino acid, so how is this made? I'm assuming after looking at the cycle and your reply to make cysteine you don't need another amino acid, while it can however undergo transamination later on.