Notes on Amino Acid Classification

Introduction

• Discussing classification of amino acids in biochemistry.
• 20 standard amino acids involved in protein synthesis.
• Discovery of 21st (selenocysteine) and 22nd (pyrolysin) amino acids.

Amino Acid Classification

Amino acids are classified based on four criteria:

1. Structural Classification
2. Polarity
3. Nutritional Requirement
4. Metabolic Fate

1. Structural Classification

• Types of Structural Classification:
  • Aliphatic Side Chain:
    • Simple Amino Acids: Glycine, Alanine
    • Branched Chain Amino Acids: Valine, Leucine, Isoleucine
    • OH Group Containing:
      • Mnemonic: "Oh, Thai, Saree, Thread"
      • Includes: Tyrosine, Serine, Threonine
    • Sulfur-Containing: Methionine, Cysteine
    • Acidic Amino Acids: Aspartic Acid, Glutamic Acid
    • Amide Group Containing: Asparagine, Glutamine
    • Basic Amino Acids:
      • Mnemonic: "His Basics are Loose"
      • Includes: Histidine, Arginine, Lysine

2. Polarity Classification

• Polar Amino Acids (Hydrophilic):

  • Charged:
    • Negatively Charged: Aspartic Acid, Glutamic Acid
    • Positively Charged: Histidine, Lysine, Arginine
  • Uncharged: Glycine, Serine, Threonine, Asparagine, Glutamine

• Non-Polar Amino Acids (Hydrophobic):

  • Includes:
    • Aromatic: Phenylalanine, Tyrosine
    • Branched Chain: Valine, Leucine, Isoleucine
    • Methionine, Alanine

3. Nutritional Requirement Classification

• Essential Amino Acids:
  • Must be obtained from diet (not synthesized by the body)
  • Mnemonic: "Mat Will Fly"
  • Includes: Methionine, Arginine, Threonine, Tryptophan, Valine, Isoleucine, Leucine, Phenylalanine
  • Arginine is semi-essential (needed in growth or pregnancy)
• Non-Essential Amino Acids:
  • Synthesized by the body

4. Metabolic Fate Classification

• Glucogenic Amino Acids:
  • Can be converted to glucose
• Ketogenic Amino Acids:
  • Converted to ketones or fats
  • Exclusively Ketogenic: Leucine
  • Predominantly Ketogenic: Lysine
• Both Glucogenic and Ketogenic:
  • Includes: Aromatic Amino Acids (Phenylalanine, Tyrosine, Tryptophan, Isoleucine)

Conclusion

• Four classifications of amino acids are crucial for understanding biochemistry.
• Important for MCQs in university exams and NEET.
• Reminder to engage with further educational content.

Additional Notes

• Focus on key amino acids for exams.
• Review mnemonics for easier recall.