Proteins: Functions and Examples

Proteins: Functions

• Proteins are large, complex molecules that perform various essential functions within the body.
• They are responsible for the construction, function, and control of tissues and organs.
• Proteins are composed of amino acids linked together in chains.
• The sequence of amino acids determines the unique three-dimensional structure and function of each protein.

Examples of Protein Functions

• Antibodies help protect the body by binding to foreign particles like viruses and bacteria.
  • Example: Immunoglobulin G (IgG)
• Enzymes carry out chemical reactions within cells and assist in the formation of new molecules.
  • Example: Phenylalanine hydroxylase
• Messenger Proteins transmit signals to coordinate biological processes between cells, tissues, and organs.
  • Example: Growth hormone
• Structural Support Proteins provide structure and support for cells and facilitate movement.
  • Example: Actin
• Transport/Storage Proteins bind and carry atoms and small molecules within cells and throughout the body.
  • Example: Ferritin

Amino Acids: Properties

• Building Blocks of Proteins: Amino acids are the basic units that form proteins.
• Amine and Acid Groups: All amino acids have an amine group (NH2) and an acid group (COOH).
• Zwitterions: Amino acids exist in a neutral state called zwitterion, where they have both positive and negative charges.
• pH Sensitivity: The carboxyl and amino groups are sensitive to pH changes, affecting their protonation or deprotonation.

Amino Acid Subgroups

• Amino acids are categorized into four subgroups based on the properties of their side chains:
  • Nonpolar (Hydrophobic) and Uncharged: These amino acids repel water.
    • Examples: Alanine, Glycine, Isoleucine, Methionine, Phenylalanine, Proline, Tryptophan, Valine
  • Polar (Hydrophilic) and Uncharged: These amino acids attract water.
    • Examples: Asparagine, Cysteine, Glutamine, Serine, Threonine, Tyrosine
  • Acidic (Polar and Charged): These amino acids have a negative charge.
    • Examples: Aspartic acid, Glutamic acid
  • Basic (Polar and Charged): These amino acids have a positive charge.
    • Examples: Arginine, Histidine, Lysine

Peptide Bonds

• Peptide bonds are formed between two amino acids through a dehydration reaction, releasing a water molecule.
• The resulting amide group is the peptide bond.
• Two amino acids linked together form a dipeptide.
• Peptide bonds have a flat, planar structure.
• Examples of peptides: Oxytocin and vasopressin, which are involved in social processes.

Levels of Protein Structure

• Fundamental Level: Primary structure refers to the sequence of amino acids in a protein chain.
• Folding and Shape: Secondary structure involves the folding of the polypeptide chain into specific arrangements like alpha-helices and beta-sheets, held together by hydrogen bonds.
• Three-Dimensional Arrangement: Tertiary structure describes the overall three-dimensional shape of a protein, stabilized by interactions between amino acid side chains, including hydrogen bonds, salt bridges, disulfide bonds, and hydrophobic interactions.
• Multiple Polypeptide Chains: Quaternary structure exists when multiple polypeptide chains (subunits) assemble to form a functional protein complex.

Protein Denaturation

• Denaturation disrupts the secondary and tertiary structures of a protein without breaking peptide bonds.
• Denaturation unfolds the protein, destroying its alpha-helices and beta-sheets.
• Factors that cause denaturation include heat, pH changes, and reducing agents.
• Denaturation typically results in protein precipitation or coagulation.

This quiz covers the essential functions of proteins within the body, highlighting their role in constructing and controlling tissues and organs. Learn about different types of proteins such as antibodies, enzymes, messenger proteins, structural support proteins, and transport proteins. Test your knowledge on the significance of protein structure and its various functions.