Twenty amino acids are encoded by the standard genetic code, but what builds them and where? tRNA transfers amino acid to ribosome, but where does it get it from?

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Nevermind. The answer is nutrition.

http://en.wikipedia.org/wiki/Essential_amino_acid

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The body can build 12 of the 20 amino acids inside the cell... this does require enzymes which are made of proteins though.

Th remaining 8 amino acids are essential, meaning that we don't have enzymes to build them, and so we have to get them from the food that we eat. Protein rich foods (like meat, beats, rice, wheat and tofu) get broken down into individual amino acids which are then transported in the blood to all the cells of the body.

Any amino acids that are not needed get broken down for energy, or stored as fat (we cannot store excess amino acids).

Amino acids are also recycled within the cell. Some proteins are only needed when a cell is dividing, for example. Once the cell is done dividing, that protein gets broken down (by other proteins) to individual amino acids.

Free amino acids, whether produced by the cell, obtained from food, or recycled within the cell, then hook up with their proper tRNA to build the next protein that you need.

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Twenty amino acids are encoded by the standard genetic code, but what builds them and where? tRNA transfers amino acid to ribosome, but where does it get it from?

tRNA carries a message from the cell nucleus (where DNA is stored) to the Ribosome where it is then run through like a computer program to construct an amino acid chain that becomes a protein.

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It's mRNA (transcribed from DNA) that carries the message out of the nucleus to the ribosomes.

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