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What is location of non-essential amino acids synthesis in a cell? Is it some specific organelle? And what is the gene driver behind this?

I thought the whole point of DNA is coding for how to synthesize proteins and that it is the mechanism of genes expression. Triplets of nucleotides are codes of amino acids and that is the granularity that cell works with.

Now it turns out cells knows how to synthesize more than half of the 20 amino acids, in humans, and I do not see, in the web, good texts of how it is done, where, and how that is coded.

Thank you for helping to shed some light.

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  • $\begingroup$ This is a very basic question, the answer to which is easy to find on the internet. Did you search Wikipedia for Essential Amino Acids or Amino Acid Synthesis? If that is insufficient and you need a biochemical text book chapter, Berg et al. on NCBI Bookshelf should be your next port of call. The specific section is in Chapter 24. Your expression "gene driver" is unclear to me. Read the chapter and then explain any further questions. $\endgroup$ – David Jul 1 at 10:15
  • $\begingroup$ Hardly it is a basic question, David. I did go through the wikipedia articles but I did not manage to answer the title question. I am a computer programmer, I have no formal education in molecular biology. $\endgroup$ – Срба Jul 4 at 21:00
  • $\begingroup$ Consider the response if I posted a question on Stack Overflow asking what a “for loop” was (for). Not only would I be posting a basic question to the wrong sort of site, but I would have shown a singular lack of initiative or aptitude in using the resources of the internet. $\endgroup$ – David Jul 4 at 21:10
  • $\begingroup$ You are showing a lack, that is sure. Quite singular $\endgroup$ – Срба Jul 8 at 20:35
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I think you are almost right. DNA (in the nucleus) is transcribed to mRNA, and protein synthesis occurs on ribosomes where the the sequence of bases in the mRNA is translated into protein. Ribosomes are located in the cytoplasm or attached to the endoplasmic reticulum. (The 'mRNA story' is well told in Who discovered mRNA?)

But there is also another type of RNA that is critical to protein synthesis, and that is transfer RNA (tRNA): each amino acid is attached to an 'adaptor' molecule (tRNA) and it is this form of the amino acid that is used by the ribosome. It is the adaptor molecule (a tRNA 'charged' with an amino acid) that contains the anti-codon, which base-pairs with the mRNA during protein biosynthesis.

In order to carry out protein biosynthesis, the cell needs a supply of amino acids, the 'building blocks' of proteins. It is here your thinking (maybe) is a little confused? The building blocks may come the digestion of protein in food, or they may be synthesized by the organism. If they can be synthesized 'de novo', perhaps starting from a glycolytic or Krebs cycle intermediate, they are (usually) considered non-essential. What amino acids are considered essential or non-essential depends on the organism. Humans, for example cannot synthesize 'de novo' the aromatic amino acids Phe, Tyr or Trp, but we can convert Phe to Tyr. E.coli, on the other hand, can make all three of these amino acids from simple building blocks, but cannot convert Phe to Tyr (see Miller & Simmonds). Thus Tyr is considered non-essential for humans (provided that an adequate supply of Phe is available).

The biochemical pathways leading to amino-acid biosynthesis are usually quite complex, with the involvement of many gene products (enzymes). The story of amino acid biosynthesis is well told in Umbarger(1978):Amino Acid Biosynthesis and its Regulation.

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There are several enzymes involved in amino acid biosynthesis. These some of thse enzymes are encoded in the human genome. You can check out KEGG for a detailed pathway in different organisms.

enter image description here

The green arrows denote reactions (and enzymes) that are present in a given organism (Homo sapiens, in this case). If you click on the arrows you can know the details about the enzyme.

These enzymes are present in the cytoplasm as well as in mitochondria. Moreover, the reactants for synthesis of certain amino acids are produced in mitochondria (TCA cycle intermediates). See this article on the role of mitochondria in amino acid metabolism.

enter image description here Overview of the amino acid metabolic network in human mitochondria. Shaded areas represent the cytoplasmic segments of the pathways.

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  • $\begingroup$ I lack chemistry knowledge in order to understand the answer fully. Thank you for answering - it gives some key hints and introductions to the topic and has quite good links. One thing perplexies me still - enzymes are transcribed & translated from DNA which are to participate in non-essential amino acids sythesis, but for the translation you need amino-acid building blocks. So it might happen the same amino acid is needed,which is then a recursive task? Seems I have to read more to understand,I am also a layman in molecular biology $\endgroup$ – Срба Jul 4 at 20:51

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