Biochemistry Lecture 4: Weak Acids and Amino Acids

Weak Acids and pH Control

• Weak acids and their conjugate bases form buffer solutions that resist changes in pH when strong acids or bases are introduced.
• When equal concentrations of weak acid and its conjugate base are present, the system can effectively neutralize added strong acids (H⁺ ions) or bases (OH⁻ ions), maintaining pH stability.

Enantiomers vs. Diastereomers

• Enantiomers are non-superimposable mirror images of each other, having opposite configurations at all chiral centers and similar physical properties, except for their interaction with polarized light.
• Diastereomers differ in configuration at one or more (but not all) of their chiral centers, leading to different physical and chemical properties, unlike enantiomers.

Common Amino Acids

• There are 20 standard amino acids, each with a unique name and code:
  • Alanine (Ala, A)
  • Arginine (Arg, R)
  • Asparagine (Asn, N)
  • Aspartic Acid (Asp, D)
  • Cysteine (Cys, C)
  • Glutamic Acid (Glu, E)
  • Glutamine (Gln, Q)
  • Glycine (Gly, G)
  • Histidine (His, H)
  • Isoleucine (Ile, I)
  • Leucine (Leu, L)
  • Lysine (Lys, K)
  • Methionine (Met, M)
  • Phenylalanine (Phe, F)
  • Proline (Pro, P)
  • Serine (Ser, S)
  • Threonine (Thr, T)
  • Tryptophan (Trp, W)
  • Tyrosine (Tyr, Y)
  • Valine (Val, V)

Classification of Amino Acids

• Amino acids can be categorized based on side chain polarity:
  • Non-polar: Hydrophobic side chains, e.g., Leucine, Isoleucine, Valine.
  • Polar: Hydrophilic side chains, e.g., Serine, Threonine, Asparagine.
  • Intermediate: Exhibit properties of both polar and non-polar amino acids, e.g., Tyrosine.

Ionizable Side Chains

• Certain amino acids possess side chains that can gain or lose protons at physiological pH, allowing them to act as weak acids or bases.
• Ionizable side chain amino acids include Aspartic Acid, Glutamic Acid, Histidine, Cysteine, and Tyrosine.

Structures of Amino Acids

• Familiarity with the structures of all 20 common amino acids is crucial for understanding their function and interactions in protein synthesis and metabolism.
• Each amino acid contains a central carbon atom, an amino group, a carboxylic acid group, a hydrogen atom, and a distinctive side chain (R group) that determines its properties.

This quiz covers the key concepts from Lecture 4, focusing on weak acids and their role in pH regulation, as well as the comparison of enantiomers and diastereomers. Additionally, it includes the classification of amino acids based on their side chain polarity and requires knowledge of their names and codes. Test your understanding of these fundamental biochemistry topics.