How many types of amino acids are present in protein ?

Explanation

**Step-by-Step Solution:**

1. **Understanding Proteins**: Proteins are macromolecules that play crucial roles in biological processes. They are composed of smaller units called amino acids.

2. **Nature of Proteins**: Proteins are classified as hetero polymers, meaning they are made up of different types of monomers (in this case, amino acids).

3. **Types of Amino Acids**: There are 20 different types of amino acids that are commonly found in proteins. These amino acids are the building blocks of proteins.

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