While roughly 500 amino acids have been identified in nature, the answer depends on the context.
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In the context of protein synthesis in the human body, 20 amino acids are typically considered. These are often called the standard or canonical amino acids.
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In the broader context of nature, approximately 500 amino acids have been identified. These include non-proteinogenic amino acids, which are not incorporated into proteins during translation.
Therefore, the answer is context-dependent, but it is most accurate to say that roughly 500 amino acids exist in nature. However, only 20 are commonly used in human protein synthesis.
