1. The Davson-Danielli model proposed a "protein sandwich" model where the phospholipid bilayer was coated with a layer of protein.
2. Biological studies that showed the Davson-Danielli model to be incorrect:
- Proteins vary in size, shape, and function and are not all present in a uniform layer.
- Antibody tagging experiments showed membrane proteins were fixed and not fluid.
- Proteins extracted from membranes were found to be insoluble in water (hydrophobic), indicating they were embedded within the bilayer, not just on the surface.
3. Functions of the plasma membrane components:
- Cholesterol: Regulates membrane fluidity and structure.
- Channel and carrier proteins: Facilitate transport across the membrane.
- Peripheral proteins: Bind to the surface; involved in cell signaling and structural support.
- Enzymes: Catalyze chemical reactions on the cell surface.
- Hormone receptor proteins: Bind hormones for signal transduction.
- Adhesion proteins: Mediate cell-cell and cell-matrix interactions.
- Neurotransmitter receptors: Bind neurotransmitters for neural signaling.
4. A single phospholipid has both polar (hydrophilic) head and nonpolar (hydrophobic) tail regions.
5. Hydrophilic heads face outward toward aqueous environments, while hydrophobic tails face inward, creating a semipermeable barrier that allows small, nonpolar molecules to pass through.
Parent Tip: Review the logic above to help your child master the concept of cell membrane transport worksheet.
