Chapter Notes on Hydroxyviscine, Proteins, and Stereochemistry

  • Hydroxyviscine and Post-Translational Modifications

    • Hydroxyviscine stabilizes modifications in proteins.
    • Methylation: Generally deactivates proteins, limiting lysine reactivity.
    • Carboxyglutamate increases negative charge, altering protein function.
    • Desmozine and Selenocysteine: Unusual amino acids introduced post-translationally, demonstrating diversity in protein structures.
    • Post-Translational Modifications (PTM): Changes in proteins after they are synthesized; examples include phosphorylation, acetylation, and methylation.

  • Phosphorylation and Signaling

    • Phosphorylation can activate or deactivate proteins, crucial for cell signaling.
    • Examples:
    • GAP (GTPase-Activating Protein): Important for sensing environmental stiffness.
      • Integrins bind extracellular matrix proteins, affecting cell behavior and nucleus permeability.
      • Phosphorylation prevents GAP from entering the nucleus, leading to its degradation and impacting gene transcription.
      • Reversible Modifications: Such as phosphorylation and acetylation, often regulate gene expression.

  • Epigenetics

    • Focuses on how gene expression changes without altering DNA sequence.
    • Study Example: Mice exposed to predator cues show altered DNA methylation, which can be inheritable.
      • This results in behavioral changes across generations without genetic mutations.
    • Environmental impacts (like pesticides on fathers) can affect offspring predispositions to diseases like ovarian cancer.

  • Role of Peptides

    • Peptides serve as signaling molecules (e.g., hormones like insulin, oxytocin) and potential antibiotics.
    • Pheromones: Used in marketing by some colognes, though their actual effectiveness is debated.

  • Stereochemistry

    • Definition: Study of the 3D arrangement of atoms in molecules. Handedness (chirality) is crucial.
    • Tetrahedral Structure: If a carbon has four different groups, it displays handedness.
    • Types of Isomers:
    • Constitutional Isomers: Different connectivity (e.g., ethanol vs. dimethyl ether).
    • Stereoisomers: Same connectivity but differ in spatial arrangement.
      • Enantiomers: Non-superimposable mirror images (e.g., amino acids).

  • Fischer Projections

    • Technique to represent 3D molecules in 2D. Important for determining configurations of chiral centers.
    • Determining Configuration (R/S): Identify priorities based on atomic weight; clockwise (R) or counterclockwise (S) direction determines configuration.
    • Spatial orientation is key; flipping a molecule changes the configuration if the lightest group is on the right/left.
    • The difference in orientations alters apparent configurations in amino acids, emphasizing the necessity of 3D modeling.

  • Optical Activity

    • Identifying enantiomers through polarized light and determining how much rotation occurs when passed through.
    • The left rotation indicates L-enantiomer; right indicates D-enantiomer.
    • Polarimeter Use: Measure optical activity comparing unknown compounds to a standard (often glyceraldehyde) to establish relative configurations.
      • Absolute Configuration: Determined by understanding specific connectivity rather than relative to a standard.

  • Conclusion on Enantiomers

    • Significant distinctions exist between D/L configurations (relative) and R/S configurations (absolute).
    • Awareness is necessary for drug development, as enantiomeric forms can lead to different physiological responses.
    • Diversity of configurations highlights the importance of stereochemistry in biological processes and pharmaceutical applications.