Amino Acids

Amino Acids Overview

  • Amino Acids as Building Blocks

    • Proteins are constructed from amino acids.

    • Over 500 amino acids are found in nature, but only 20 are genetically encoded in humans.

    • Essential Amino Acids: Must be obtained from the diet.

    • Non-Essential Amino Acids: Synthesized by the body.

Learning Outcomes for Biochemistry

  • Reflect on the achievements of biochemists and their importance.

  • Understand the structure and function of amino acids and proteins.

  • Acknowledge the role of chemistry in biochemistry development.

  • Recognize the relevance of amino acids in enzymes and biochemical reaction mechanisms.

  • Learn about the metabolical importance of amino acids and proteins.

Classification of Amino Acids

  • Amino acids are categorized into groups based on their chemical properties:

    • Aliphatic: Examples include Alanine (A), Glycine (G), Valine (V).

    • Aromatic: Phenylalanine (F), Tryptophan (W), Tyrosine (Y).

    • Acidic: Aspartic acid (D), Glutamic acid (E).

    • Basic: Arginine (R), Lysine (K), Histidine (H).

    • Sulfur-Containing: Cysteine (C), Methionine (M).

    • Amidic: Asparagine (N), Glutamine (Q).

Historical Context

  • Amino acids are among the earliest organic molecules on Earth and have evolved from the Hadean to the present.

  • Significant eons in amino acid synthesis:

    • Hadean: Formation of Earth and initial molecular structures.

    • Archean: Rise of bacteria and archaea.

    • Proterozoic: Gathering of oxygen.

    • Phanerozoic: Diversification of life.

Synthesis and Functional Importance

  • Early selection of amino acid structures influenced by biophysical properties affecting protein folding.

  • Recognition of the amino acid alphabet impacted protein synthesis.

Protein Structure and Function

  • Amino acids play pivotal roles in nitrogen fixation and metabolism, including:

    • Nitrogen Fixation: The process by which nitrogen is converted into a usable form by bacteria.

    • Protein Structures: Include primary (amino acid sequence), secondary (helix/sheet formations), tertiary (3D structure), and quaternary structures (multiple polypeptides).

General Structure of Amino Acids

  • All amino acids share a common structure:

    • Central α-carbon.

    • An amino group (NH2).

    • A carboxylic acid group (COOH).

    • A hydrogen atom (H).

    • A unique side chain (R group) that defines the amino acid type.

Ionization and Zwitterion Formation

  • Amino acids at physiological pH (7.4) exist primarily as zwitterions:

    • Carry no net charge due to the ionization of the amino and carboxyl groups, acting as weak acids and bases.

pH and Amino Acid Behavior

  • pH influences amino acid charge states:

    • Isoelectric Point (pI): pH at which amino acid has no net charge.

    • Amino acids can have acidic or basic properties depending on their side chains (e.g., aspartic acid, lysine).

Polar and Non-Polar Variations

  • Side chain polarity affects aqueous solubility:

    • Polar Side Chains: Hydrophilic, containing hydroxyl or charged functional groups (Serine, Threonine).

    • Non-Polar Side Chains: Hydrophobic, lack charged groups (Leucine, Methionine).

Biological Roles of Amino Acids

  • Energy Metabolism: Serve as nutrients and energy substrates.

  • Function as neurotransmitters (e.g., dopamine derived from tyrosine).

  • Act in metabolic pathways (e.g., urea cycle intermediates).

  • Methylation: Universal methyl donor role by S-adenosylmethionine (SAM).

Enantiomers and Chirality

  • Most amino acids are chiral (except glycine) and exist as D and L forms:

    • CORN Rule: Determines L and D configurations of amino acids.

Relevance to Biochemistry Studies

  • Importance of understanding amino acids' roles in enzyme mechanisms and metabolic pathways for further studies in biochemistry.