Cell Membranes and Organelles Study Notes

Gangliosides and Organelles

  • Gangliosides are lipids found in neurons.
  • Produced primarily in the smooth endoplasmic reticulum (ER).
  • Function of smooth ER: lipid production and detoxification of toxins.

Enzymes and Breakdown

  • Hexosaminidase: enzyme that breaks down gangliosides; located in lysosomes.

Protein Synthesis and Transport

  • Ribosomes on rough ER synthesize proteins.
  • Proteins are transported to the Golgi apparatus via transport vesicles.
  • Golgi modifies and sorts proteins before sending them to the cell membrane.

Biological Membranes

  • Cell membranes define the boundaries of cells; consist of a lipid bilayer.
  • Membranes are essential for compartmentalization of cellular functions.
  • All cells (prokaryotic and eukaryotic) have a plasma membrane.

Cytoplasm and Cytosol

  • Cytoplasm: includes all non-nuclear content within a cell.
  • Cytosol: the aqueous component of the cytoplasm, primarily water (65%).

Membrane Structure

  • Phospholipid bilayer: contains hydrophilic heads (polar) and hydrophobic tails (nonpolar).
  • Cholesterol in membranes modulates fluidity: may make more fluid or less fluid depending on surrounding lipids.
  • Proteins embedded within membranes facilitate various functions (transport, recognition, etc.).

Fluid Mosaic Model

  • Describes membrane structure as fluid and composed of a mosaic of different components (lipids, proteins, carbohydrates).
  • Membrane components can move laterally within the layer but cannot easily flip between layers.

Membrane Proteins

  • Different types of proteins perform diverse roles: transport, signaling, recognition, anchoring, etc.
  • Protein structure is influenced by their environment—hydrophobic amino acids face inward and hydrophilic amino acids face outward.

Transport and Permeability

  • Membranes are semi-permeable: allow certain molecules (nonpolar substances) through but restrict polar/charged substances (e.g., ions).
  • Osmosis: movement of water across a membrane from high to low concentration, crucial for cellular function.
  • Proteins are needed for the transport of ions and larger polar molecules across the membrane.