Proteins and Cell Membrane Transport

Protein Classification

• Peripheral proteins make up 10% of membrane proteins, while integral proteins make up 90%
• Integral proteins are transmembrane or in-wall, meaning they span across the membrane or are embedded in it

Transport Mechanisms

Passive Transport

• Occurs along the concentration gradient, requiring no energy
• Examples include passive diffusion, where molecules move from an area of higher concentration to an area of lower concentration

Facilitated Diffusion

• Involves the use of channel proteins or carrier proteins to facilitate transport
• Channel proteins form a pore or channel in the membrane, allowing specific molecules to pass through
• Examples include porin proteins

Active Transport

• Transport occurs against the concentration gradient, requiring energy consumption
• Examples include the Na+ pump, which transports sodium ions into the cell against their concentration gradient

Osmosis

• Movement of water molecules from an area of higher concentration to an area of lower concentration
• Occurs through a selectively permeable membrane, allowing polar molecules like water to pass through

Plasma Membrane

• Discovered by Singer and Nicolson in 1972
• Labeling proteins on the membrane surface confirms the fluid mosaic model, where proteins are able to move laterally but do not flip-flop across the membrane

Glycoproteins and Cell Recognition

• Glycoproteins, or sugar-proteins, are important for cell-to-cell recognition
• They provide mobility and flexibility to the cell surface, allowing for interactions with other cells