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Proteins

  • Proteins are essential to every living cell.

  • Major components in:
      - Hair
      - Skin
      - Muscle

  • Functions of proteins include:
      - Transporting oxygen, nutrients, and minerals through the bloodstream
      - Acting as chemical messengers (hormones)
      - Catalyzing the chemistry of life (enzymes)

Naturally Occurring Amino Acids

  • Definition:
      - The general formula for an amino acid includes four groups attached to a carbon atom:
        1. Carboxylic acid group, −COOH
        2. Amine group, −NH2
        3. Hydrogen atom, −H
        4. Side chain designated as R

  • Proteins are classified as polyamides or polypeptides, which are polymers made up of amino acid monomers.

  • Majority of proteins are constructed from various combinations of 20 different naturally occurring amino acids.

Structure of Amino Acids

  • General structure depicted as:

      H3N+−C−C(R)extwhereRisthesidechainH_3N^+-C-C(R) ext{ where R is the side chain}

      | |
      | | ------ (Carboxylic acid)
      | |
      | | ------ (Amine)
      | |
      | | ------ (Hydrogen)

Amino Acid Side Chain Groups

  • Side chains can be classified as:
      - Polar
      - Nonpolar

Characteristics of Side Chain Groups

  • Nonpolar Groups:
      - Tend to be hydrophobic
      - Associate with one another to avoid interaction with water
      - Interact via London dispersion intermolecular forces

  • Polar Groups:
      - May interact via:
        - Hydrogen bonding intermolecular forces
        - Attraction of ionic charges (acidic or basic groups, e.g., carboxylic acids or amines)

Peptide Bonds

  • Definition:
      - A peptide bond is formed when two amino acids link together by expelling a water molecule.

  • The process can repeat, leading to the creation of a peptide chain.

  • Once incorporated into the peptide chain, the amino acids are termed amino acid residues.

Essential Amino Acids

  • Importance:
      - The protein that is formed depends on the types and sequence of amino acids present in the peptide.

  • Some amino acids, known as essential amino acids, cannot be synthesized by humans; they must be ingested through diet.

  • Regular food intake is necessary to replenish the body's proteins, which are constantly broken down and rebuilt.

List of Essential Amino Acids

  1. Histidine

  2. Lysine

  3. Threonine

  4. Isoleucine

  5. Methionine

  6. Tryptophan

  7. Leucine

  8. Phenylalanine

  9. Valine