Comprehensive Cell Biology Notes

Cell Membrane Structure and Function

• Phospholipid Bilayer:
  • Arrangement of hydrophilic heads and hydrophobic tails.
  • Creates selective permeability.
• Membrane Proteins:
  • Channel Proteins: Regulate molecular transport.
  • Receptor Proteins: Involved in cell signaling and molecular transport; regulation can be chemical or electrical. Examples include those involved in cigarette addiction and HIV resistance.
  • Integral Proteins: Embedded within the membrane.
  • Peripheral Proteins: Located on the membrane surface.

Molecular Transport Mechanisms

• Passive Transport: Requires no energy.
  • Diffusion: Movement of molecules from high to low concentration.
  • Facilitated Diffusion: Movement of molecules through a protein channel, from high to low concentration.
  • Osmosis: Movement of water across a semi-permeable membrane from an area of low solute concentration to high solute concentration.
    • Crucial for fluid balance.
    • Salt concentration affects water movement and blood pressure.
    • Clinical significance: isotonic, hypertonic, and hypotonic solutions.
• Active Transport: Requires energy (ATP).
  • Moves molecules against their concentration gradients.
  • Maintains ion gradients.
  • Primary Active Transport
  • Secondary Active Transport
  • Sodium and potassium pumps are vital for nerve impulse transmission and muscle contraction.
• Endocytosis: Cell takes in substances.
  • Receptor-Mediated Endocytosis: Targeted molecule intake.
  • Pinocytosis: Fluid intake.
  • Phagocytosis: Cellular ingestion of pathogens or debris, primarily by immune cells like macrophages; important for immune defense.
• Exocytosis: Cell expels waste.

Cell Organelles and Their Functions

• Nucleus:
  • Houses DNA and nucleolus.
• Endoplasmic Reticulum:
  • Rough ER: Protein synthesis.
  • Smooth ER: Lipid and carbohydrate synthesis.
• Golgi Apparatus:
  • Modifies, packages, and distributes molecules.
  • Target of protease inhibitors in HIV treatment, disrupting protein modification.
• Ribosomes:
  • Protein synthesis.
• Mitochondria:
  • ATP production and cellular respiration.
  • Contains its own DNA (maternally inherited); evolutionary significance in tracing human ancestry.
• Lysosomes:
  • Digestive enzymes.
• Peroxisomes:
  • Detoxification and fatty acid breakdown.
• Cytoskeleton:
  • Maintains cell shape.
• Cilia, Microvilli, Flagella:
  • Cellular movement and absorption.

Clinical Connections and Examples

• Cigarette Addiction: Mediated by receptor proteins.
• HIV Resistance: Linked to genetic mutations affecting receptor protein configuration.
• Protease Inhibitors: Used in HIV treatment; target the Golgi apparatus and disrupt protein modification.
• IV Fluids: Isotonic, hypertonic, and hypotonic solutions used in clinical care.

Key Insights

• Cell Membrane Dynamics:
  • Phospholipid bilayer creates a semi-permeable barrier.
  • Embedded proteins act as specific gatekeepers, controlled by chemical and electrical signals.
  • Fluid mosaic model underscores the membrane’s adaptability.
• Osmosis and Salt Concentrations:
  • Movement of water across membranes is driven by salt gradients.
  • Explains fluid balance in the body and the effect of salt intake on blood pressure.
  • Essential knowledge in clinical care for administering IV fluids.
• Active Transport:
  • Requires ATP to move molecules against their concentration gradients.
  • Maintains vital electrochemical gradients (e.g., sodium and potassium pumps).
  • Critical for nerve impulse transmission, muscle contraction, and cellular viability.
• Endocytosis Types:
  • Pinocytosis: Fluid intake.
  • Receptor-Mediated Endocytosis: Targeted molecule intake.
  • Phagocytosis: Cellular ingestion of pathogens or debris.
  • Sophisticated mechanisms for maintaining homeostasis and defending the body from infection.
• Mitochondrial DNA:
  • Maternally inherited, allowing the tracing of human ancestry.
  • Connects cellular biology to anthropology and evolutionary medicine.
• Mutations in Receptor Proteins:
  • Can confer disease resistance (e.g., HIV resistance).
  • Influences susceptibility to viral infections.
  • Leads to innovative approaches in gene therapy and drug development.
• Protease Inhibitors:
  • Disrupt viral life cycle through interference with protein modification in the Golgi apparatus.
  • Highlights the therapeutic relevance of cellular organelles.

Equations and Formulas

• (\sqrt{9} = 3)