Lecture Notes on Phospholipids, Steroids, and Proteins

Phospholipids

• Definition: A type of fat called phospholipid, characterized by a lipid portion with a phosphate group.
  • Structure: Comprised of a glycerol backbone, one fatty acid chain, and a phosphate-containing polar group.
  • Terminology: The polar group is referred to as a phosphate group.
• Location: Found only in cell membranes.
  • Structure Depiction: Polar head (round portion) and non-polar tails (fatty acid chains).
• Cell Membrane Environment:
  • Extracellular and intracellular fluids are mainly water.
  • Phospholipid bilayer forms the cell membrane structure.
  • Polar heads: Hydrophilic, interact with water.
  • Non-polar tails: Hydrophobic, do not interact with water.
• Amphipathic Nature:
  • Phospholipids are both hydrophilic (head) and hydrophobic (tail).

Steroids

• Definition: A type of fat-derived hormone.
• Types of Hormones: Fat hormones (steroids) and protein-based hormones.
• Cholesterol:
  • Base molecule for steroid hormones (e.g., testosterone, estrogen).
  • Produced via de novo synthesis, not heavily reliant on dietary intake.

Proteins

• Types:
  • Structural Proteins: Form the shape and support of the body (e.g., bones, hair).
  • Functional Proteins: Perform specific roles (e.g., enzymes, hormones, antibodies).
• Amino Acids:
  • Building blocks of proteins.
  • Human body uses 20 types of amino acids.
  • Essential amino acids must be ingested in diet; non-essential can be synthesized internally.
• Protein Structure:
  • Primary Structure: Linear sequence of amino acids.
  • Secondary Structure: Alpha helix formed by hydrogen bonding.
  • Tertiary Structure: Complex 3D folding, forms globular proteins.
  • Quaternary Structure: Multiple tertiary structures combined (e.g., hemoglobin).
• Importance of Complete Amino Acid Profile:
  • Necessary for protein synthesis and repair.
  • Vegetarians need to combine specific foods to obtain all essential amino acids.
  • Historic error in protein drinks led to health issues due to missing amino acid.

ATP and Protein Function

• ATP (Adenosine Triphosphate):
  • Role in changing protein shapes by adding phosphate groups, breaking hydrogen bonds.
  • Misconception as "energy of the body"; primarily involved in protein conformation changes.

Protein Denaturation

• Definition: Loss of protein function due to excessive bond breaking and shape change.
• Causes:
  • Extreme pH shifts (e.g., acidosis) and high temperatures (e.g., fever > 104°F).
• Consequences:
  • Proteins become non-functional, leading to physiological failure.