🧬 Amino Acids – Structure, Properties, and Zwitterions
Amino acids are fundamental building blocks of proteins—and they are guaranteed to appear on the DAT. You’ll be tested on their structure, acid-base behavior, side chain properties, and zwitterion formation.
Today’s breakdown:
Amino acid structure basics
Side chain classifications (polar, nonpolar, acidic, basic)
Zwitterions and pKa behavior
DAT-style examples to lock it in
🔬 Basic Amino Acid Structure
| Group | Structure Component |
|---|---|
| Central Carbon (Cα) | Center of molecule |
| Amino Group (-NH₂) | Basic group (accepts H⁺) |
| Carboxyl Group (-COOH) | Acidic group (donates H⁺) |
| R Group (Side Chain) | Determines identity and properties |
🧠 All amino acids except glycine are chiral (have 4 different groups attached).
🌟 Amino Acid Side Chain Classifications
| Property Type | Examples |
|---|---|
| Nonpolar (Hydrophobic) | Glycine, Alanine, Valine |
| Polar (Uncharged) | Serine, Threonine, Asparagine |
| Acidic (Negatively Charged) | Aspartate, Glutamate |
| Basic (Positively Charged) | Lysine, Arginine, Histidine |
🧠 Tip: Acidic side chains have –COO⁻; Basic side chains have –NH₃⁺.
⚡ Zwitterions and pKa Behavior
At physiological pH (~7.4), amino acids exist as zwitterions:
–NH₃⁺ and –COO⁻ present simultaneously.
pKa values:
Carboxyl group pKa ≈ 2
Amino group pKa ≈ 9-10
At pH = pI (isoelectric point) → overall charge = 0
🧠 "Zwitterion = both positive and negative charges at once."
📈 DAT-Style Practice Questions
Q: What charge does an amino acid have at a pH above its isoelectric point (pI)?
A: Negative charge (deprotonated form dominates).
🎯 DAT Strategy Tips
✅ Memorize classifications (polar, nonpolar, acidic, basic)
✅ Know structure of glycine, alanine, and charged amino acids
✅ Understand zwitterion behavior at different pH
✅ Practice quick pKa and pI questions
✅ Visualize side chains and charges using KOTC diagrams
Study more visuals at kingofthecurve.org/studyscience
🚀 Call-to-Action
Want to build a strong DAT foundation?
Download the KOTC App to get:
Amino acid flashcards
Biochemistry-focused quizzes
Animations of acid-base behavior
Leaderboards + Curve Coins to track mastery
⚡ Master amino acids—be unstoppable on your DAT.
Frequently Asked Questions (FAQs)
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Aim for 4-6 focused hours, ensuring you incorporate breaks to avoid burnout.
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Practice mindfulness techniques, take practice exams under realistic conditions, and maintain a balanced lifestyle.
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Set short-term goals, seek support from mentors, and reward yourself for small achievements.
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Regular exercise improves focus, reduces stress, and enhances overall mental clarity.
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KOTC offers personalized learning tools, gamification features, and adaptive question banks to help students stay on track without burnout.
