High Yield MCAT: Introduction to the 20 Amino Acids

General Concepts

• Amino acids: Also referred to as residues.
  • 20 proteinogenic amino acids encoded by human DNA.
  • These are transcribed from DNA to mRNA and then translated into polypeptides (proteins).
  • Proteinogenic: Derived from "protein" + "genic" (gene, to produce).

Key Points

• Start codon AUG codes for Methionine.
• Memorizing all 20 amino acids is crucial for the MCAT.
• They are high-yield topics for the exam.

Methionine (Met, M)

• Abbreviations:
  • Three-letter: Met
  • One-letter: M
• Structure: Contains a sulfur in its R group.
• Classification: Nonpolar
• pKa Values: Not applicable to Methionine.
• Special Characteristics:
  • Encoded by the start codon AUG.

Amino Acid Learning Tips

• Use flashcards (virtual options: Anki, Quizlet).
  • Anki is user-friendly for adding pictures.
  • Drawing structures by hand recommended.

Fundamental Characteristics of Amino Acids

• Basic Structure:
  • Zwitterionic: Has both positive and negative charges, but a net charge of zero.
  • Physiological pH: 7.4
• N-terminus: Amino group
• C-terminus: Carboxylic acid group
• Translation direction: From N to C-terminus (5 prime end to 3 prime end of mRNA)
• R Group: Functional group that distinguishes different amino acids.
• Cα Carbon (Alpha Carbon):
  • Located one carbon away from the carbonyl carbon.
  • Each amino acid has one Cα carbon.

Additional Notes

• Eukaryotes: All amino acids have L-configuration (stereochemistry).
• C Alpha: Only chiral carbon in the amino acid backbone; R groups may also have chiral carbons.

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Reminder: Practice with flashcards, draw structures, and understand fundamental characteristics to excel in MCAT amino acid questions.