All protein amino acids have an asymmetric center except .................

Explanation

To solve the question "All protein amino acids have an asymmetric center except .................", we need to identify the specific amino acid that does not have an asymmetric center.

### Step-by-Step Solution:

1. **Understanding Protein Amino Acids**:
- Protein amino acids are the building blocks of proteins. They contain an alpha carbon (Cα) that is typically bonded to four different groups: an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom (H), and a variable side chain (R group).

2. **Definition of Asymmetric Center**:
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