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Overview of Amino Acids and Their Properties

Sep 19, 2024

Amino Acids Overview

Basic Structure

  • Carbon with four valencies:
    • Amino Group: NH2
    • Acidic Group: COOH
    • Hydrogen: H
    • R Group: Variable (sulfur, alcohol, etc.)

Definitions

Alpha Amino Acid

  • Alpha Carbon: Carbon next to the functional group.
  • Alpha Amino Acid: Amino group attached to the alpha carbon.
  • Most amino acids in the body are in alpha form. Exceptions include Beta-alanine and Gamma-amino isobutyrate.

Kerial Carbon

  • Carbon with four different groups attached.
  • Important for optical activity and mirror image formation.
  • Glycine is optically inactive because it lacks kerial carbon (two hydrogen atoms are attached).

Imino Acids

  • Example: Proline
  • Amino group is part of a ring structure and not free.

Classification of Amino Acids

Based on R Group

  1. Simple Amino Acids
    • Glycine (simplest), Alanine (most abundant)
  2. Branched-Chain Amino Acids
    • Leucine, Isoleucine, Valine
  3. Sulfur-Containing Amino Acids
    • Methionine, Cysteine
  4. Hydroxyl-Containing Amino Acids
    • Serine, Threonine, (Tyrosine - despite being non-water soluble)
  5. Acidic Amino Acids
    • Aspartate, Glutamate
  6. Amide Group Containing Amino Acids
    • Asparagine, Glutamine
  7. Basic Amino Acids
    • Histidine, Lysine, Arginine (most basic)

Based on Water Solubility

  • Hydrophilic (Polar) Amino Acids
    • Alcohol, Acid, Base, Amide
    • Glycine, Cysteine
  • Hydrophobic
    • Remaining amino acids

Based on Metabolism

  1. Ketogenic Amino Acids
    • Leucine, Lysine
  2. Glucogenic Amino Acids
    • All others except the specifically ketogenic and keto/glucogenic
  3. Keto and Glucogenic
    • Tryptophan, Phenylalanine, Tyrosine, Isoleucine

Based on Nutritional Requirement

  1. Essential
    • 9 amino acids (TV TILL 9 PMH)
  2. Semi-Essential
    • Arginine
  3. Non-Essential
    • Remaining 12 amino acids

Special Properties

Aromatic Amino Acids

  • Examples: Tryptophan, Phenylalanine, Tyrosine, Histidine
  • Properties: Absorb UV rays, Tryptophan absorbs the most.

Derived Amino Acids

  • Cannot be represented by a codon
  • Examples: Hydroxyproline, Hydroxylysine, Desmosine, Cystine, Ornithine, Citrulline

Newly Added Amino Acids

21st Amino Acid

  • Selenocysteine
  • Codon: UGA
  • Precursor: Serine

22nd Amino Acid

  • Pyrrolysine
  • Codon: UAG

This summary captures the important concepts and classifications of amino acids as presented in the lecture.

Full transcript