Show the fundamental unit of structure common to all polypeptides and proteins and show how cross linking occurs between two chains by H-bonding.

Explanation

### Step-by-Step Text Solution

**Step 1: Identify the Fundamental Unit of Polypeptides and Proteins**

The fundamental unit of structure common to all polypeptides and proteins is the amino acid. Amino acids are the building blocks that link together to form polypeptides through peptide bonds.

**Step 2: Structure of an Amino Acid**

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