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I'm fairly new learning about protein. As I know protein can be synthesis by condensation reaction. And the current method to produce protein is purify them from an organism. So why not produce protein based on condensation reaction instead of purifying it from an organism?

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can you give a link to the "condensation reaction"? I'm not sure what exactly you're referring to... – MattDMo Jul 25 '13 at 1:51
@MattDMo… – DucFabulous Jul 25 '13 at 2:07
@ĐứcUltraSoft, because it is difficult to synthesize long proteins that way.. small peptides can be synthesized like that.. – WYSIWYG Jul 25 '13 at 3:01
@WYSIWYG Thank you so much, now i understand. – DucFabulous Jul 25 '13 at 3:46
The chemical synthesis of peptides has actually been used for a long time, see the Wikipedia entry or this schematic for some examples. – nico Jul 31 '13 at 6:37

It is important to first remember that to do anything useful, the sequence of the amino acids in the protein must be exact. For example, sickle-cell anaemia is caused because one amino acid in a haemoglobin protein is incorrect. Because of this, peptide synthesis involves rather complex chemistry in order to ensure that amino acids are added in the correct order and number, and is only effect up to a chain of a few dozen amino acids.

Now it is possible to produce peptides of various lengths in a cell-free extract, which basically involves taking the cytosol out of cells (with all the ribosomes, tRNA's, and other factors therein) and adding the mRNA template to be translated and an ATP source. This way, a peptide can be prepared by using the cell's own machinery for protein synthesis without actually needing a viable cell.

Remember also that even if it were possible to chemically synthesize a correct peptide sequence, the protein would still need to fold into a correct 3-dimensional structure to work properly, which in some cases is impossible for any artificial method currently available.

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