Hereditary Spherocytosis

Opening Remarks

  • The instructor greets students and indicates they will address a misconception regarding cell organelles.

Introduction of Club Question

  • A question is presented for review: "Which of the following structures are not organelles?"

    • Options: Nucleus, Nucleolus, Cytoskeleton, Ribosomes, Centrosomes.

    • Clarification on Misunderstanding:

    • The nucleus is an organelle, but the nucleolus is not.

    • Cytoskeleton, ribosomes, and centrosomes are not considered organelles.

  • Definition of an Organelle:

    • An organelle is defined as a membrane-bound compartment. Non-membrane-bound structures are not classified as organelles.

Membrane Structure Overview

  • Introduction to the topic of cell membrane structure. Includes discussion of hereditary spherocytosis, a genetic disease.

Hereditary Spherocytosis

  • Definition: A type of anemia characterized by a deficiency of red blood cells.

  • Etymology: "Anemia"

    • "Eemia" means blood, "IA" refers to a condition, and "AN" implies a lack of.

  • Symptoms:

    • Yellowing of the eyes (jaundice) due to breakdown of red blood cells, leading to bilirubin accumulation.

    • Enlarged spleen (splenomegaly):

    • Red blood cells become spherical instead of the usual biconcave shape, leading to recognition and destruction by the spleen.

    • Other common symptoms include fatigue, dizziness, hair loss, and shortness of breath.

  • Cause of Red Blood Cell Shape Change:

    • Dysfunction of proteins (spectrin and anchoring proteins) beneath the membrane that helps maintain the biconcave shape.

Proteins in Red Blood Cells

  • Spectrin and Anchoring Proteins:

    • Mutations or dysfunctions in these structures lead to a loss of the typical flexible shape of red blood cells.

  • Cell Cortex and Cortical Cytoskeleton:

    • Definition: Specialized layer of cytoskeleton beneath the cell membrane rich in actin proteins; helps maintain shape and facilitate movement.

Membrane Components

Phospholipids and Membrane Structure

  • The membrane is composed of:

    • Lipids (primarily phospholipids)

    • Proteins

  • Components and Functionality:

    • The membrane is approximately 5 nanometers thick and consists of two lipid layers containing various proteins.

  • Types of Lipids Found in Membranes:

    1. Phospholipids: Lipids with a phosphate group. Example: Phosphatidylcholine.

    • Structure includes hydrocarbon chains and phosphate which defines hydrophobic and hydrophilic characteristics.

    1. Cholesterol: Found in animal cells (not in bacteria or plants); contributes to membrane fluidity.

    2. Glycolipids: Lipids containing carbohydrates, significant in cellular recognition and interaction.

Amphipathic Nature of Lipids

  • Definition: Molecules possessing both hydrophobic and hydrophilic parts.

    • Example: Within phospholipids, the phosphate group and certain amino acids form the hydrophilic head, while hydrocarbon chains form the hydrophobic tails.

  • This amphipathic character leads to the formation of lipid bilayers when phospholipids are placed in aqueous environments, thus protecting hydrophobic tails from water.

Bilayer Formation and Structure

  • Description of the lipid bilayer symmetry and how it forms an energetically favorable structure, sealing itself off from water.

  • One layer faces the cytosol and the other faces the extracellular space.