The core difference lies in the side chain (R group) of the amino acid: a basic amino acid has a side chain that contains an amino group, whereas not all amino acids do. This distinction affects their charge at physiological pH.
Here's a breakdown:
Amino Acids
- General Structure: All amino acids share a common structure:
- A central carbon atom.
- An amino group (-NH2).
- A carboxyl group (-COOH).
- A hydrogen atom (-H).
- A unique side chain, or R group.
- Diversity: The R group is what makes each of the 20 standard amino acids unique. These R groups can be nonpolar, polar uncharged, acidic, or basic.
- Neutrality: Many amino acids at physiological pH (around 7.4) are electrically neutral, meaning they have no overall charge, despite having both an amino and carboxyl group which can gain or lose protons.
Basic Amino Acids
- Characteristic: The key feature of a basic amino acid is its side chain containing an amino group (-NH2). This extra amino group can accept a proton (H+), giving the side chain a positive charge at physiological pH.
- Charge at Physiological pH: Due to this extra amino group, basic amino acids are positively charged at neutral pH.
- Examples: Examples of basic amino acids include:
- Lysine (Lys, K)
- Arginine (Arg, R)
- Histidine (His, H)
Comparison Table
| Feature | Amino Acid | Basic Amino Acid |
|---|---|---|
| Side Chain | Varies; can be nonpolar, polar, acidic, or basic. | Contains an amino group (-NH2). |
| Charge at pH 7.4 | Can be neutral, negative (acidic), or positive (basic). | Positive |
| Key Group in Side Chain | Varies depending on type. | Amino group (-NH2) that can gain a proton. |
Key Takeaway
The crucial difference is the presence of an extra amino group in the side chain of basic amino acids. This additional amino group allows them to gain a positive charge, making them distinct from other types of amino acids including those with acidic side chains (containing a carboxyl group that allows them to bear a negative charge), or those that are neutral at physiological pH.
