Proteins are built from a set of 20 different small parts known as amino acids, which are found in both animal and plant proteins. These amino acids are linked together in specific sequences to form polypeptide chains, which then fold into unique three-dimensional shapes to create functional proteins.
The options you provided contain some inaccuracies. Here’s a clearer breakdown:
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First Response: Incorrect – Amino acids are not exclusive to animal proteins; they are found in both animal and plant sources.
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Second Response: Correct – Proteins are indeed constructed from 20 different amino acids that are available in both animal and plant proteins.
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Third Response: Incorrect – Proteins are not made by adding extra parts to existing proteins; they are synthesized from amino acids.
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Fourth Response: Incorrect – While proteins can sometimes be refolded, they are primarily synthesized from amino acids rather than existing proteins.
In summary, proteins are synthesized from 20 different amino acids found in both animal and plant sources, and their unique functions arise from their specific sequences and structures.