Step by Step
1
Negatively charged (acidic) amino acids
Aspartate (D) and Glutamate (E) carry a negative charge at physiological pH, classifying them as acidic amino acids.
2
Positively charged (basic) amino acids
Histidine (H), Lysine (K), and Arginine (R) carry a positive charge at physiological pH, classifying them as basic amino acids.
3
Shared property: hydrophilic
All five charged amino acids are hydrophilic (water-loving), a direct consequence of carrying an electrical charge.
4
Where they're found in a folded protein
Because they're hydrophilic, charged amino acids are typically found on protein surfaces, where they can interact with the surrounding aqueous environment — the opposite location from nonpolar amino acids, covered in the next lesson.
Applied Walkthrough
1
Aspartate and Glutamate, both carrying a negative charge at physiological pH, are classified as acidic amino acids — while Histidine, Lysine, and Arginine, carrying a positive charge, are classified as basic.
2
All five of these amino acids share a key property regardless of the direction of their charge: they're hydrophilic, meaning they readily interact with surrounding water molecules.
3
This shared hydrophilic property explains exactly where these amino acids tend to be positioned within a folded protein — typically on the protein's outer surface, where they can interact directly with the surrounding aqueous cellular environment.
4
This positioning pattern — charged amino acids on the surface — stands in direct contrast to nonpolar amino acids, which instead cluster in the protein's hydrophobic interior, a distinction covered in the very next lesson.
Exam Application
Exams test whether you can correctly sort the five charged amino acids into acidic (Asp, Glu) versus basic (His, Lys, Arg) categories, and whether you understand why their shared hydrophilic property places them on a protein's surface.
⚠ Common Trap
The most common trap is confusing which charged amino acids are acidic versus basic — remember Aspartate and Glutamate are negatively charged (acidic), while Histidine, Lysine, and Arginine are positively charged (basic) — the mnemonic DEHKR keeps the full group together, but the acidic/basic split within it still needs to be memorized separately.
✓ Quick Self-Check
1. Which two amino acids are negatively charged (acidic) at physiological pH?
Aspartate (D) and Glutamate (E).
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2. Which three amino acids are positively charged (basic) at physiological pH?
Histidine (H), Lysine (K), Arginine (R).
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3. What shared property do all five charged amino acids have?
They are hydrophilic (water-loving).
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4. Where in a folded protein are charged amino acids typically found?
On the protein's surface.
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5. What does the mnemonic DEHKR stand for?
Asp, Glu, His, Lys, Arg — the five charged amino acids.
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