1. Amino Group (NH2): This is a nitrogen-containing group that is basic (can accept protons). It is attached to the alpha carbon.

2. Carboxyl Group (COOH): This is an acidic group containing a carbon atom double-bonded to an oxygen atom and also single-bonded to a hydroxyl group (-OH). It is also attached to the alpha carbon.

3. Side Chain (R Group): This is a variable group that differs between different amino acids. It is attached to the alpha carbon and determines the amino acid's unique chemical properties.

Here's a visual representation:

```

NH2

|

H - C - COOH

|

R

```

The alpha carbon: This is the central carbon atom that connects all three parts of the amino acid.

Let's break down the R groups:

* Non-polar side chains: These are hydrophobic and tend to cluster together in the interior of proteins. Examples include glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, tryptophan, and methionine.

* Polar side chains: These are hydrophilic and can interact with water. Some are uncharged (e.g., serine, threonine, tyrosine, asparagine, glutamine), while others are charged (e.g., aspartic acid, glutamic acid, lysine, arginine, histidine).

The specific R group of each amino acid determines its unique properties and how it will interact with other amino acids in a protein.