Cell Membrane Structure and Functions

Structure and Composition

• Phospholipid bilayer: a double layer of lipids with hydrophilic heads and hydrophobic tails
• Embedded proteins: integral proteins (span the membrane) and peripheral proteins (attached to the surface)
• Cholesterol molecules: embedded between phospholipids, maintaining fluidity and structure
• Carbohydrates: attached to lipids and proteins, forming glycolipids and glycoproteins

Functions

• Barrier function: regulates what enters and leaves the cell
• Cell signaling: proteins and lipids participate in signal transduction pathways
• Cell adhesion: proteins and carbohydrates facilitate cell-cell interactions
• Transport: proteins facilitate movement of molecules across the membrane
• Cell recognition: carbohydrates and proteins help identify self and non-self

Fluid Mosaic Model

• Fluidity: phospholipid bilayer is dynamic and flexible, allowing for movement of proteins and lipids
• Mosaic: proteins and lipids are arranged in a mosaic pattern, with varying degrees of mobility

Types of Transport

• Passive transport: movement of molecules down their concentration gradient (diffusion, osmosis)
• Active transport: movement of molecules against their concentration gradient, requiring energy input
• Facilitated diffusion: assisted transport of molecules down their concentration gradient
• Receptor-mediated endocytosis: uptake of molecules into the cell through receptor-mediated vesicle formation

Membrane Permeability

• Semipermeable: allows certain molecules to pass through, while restricting others
• Selective permeability: specific molecules are allowed to pass through, while others are restricted
• Permeability coefficients: measure of a molecule's ability to pass through the membrane

Cell Membrane Structure

• Phospholipid bilayer consists of a double layer of lipids with hydrophilic heads and hydrophobic tails
• Integral proteins span the membrane, while peripheral proteins attach to the surface
• Cholesterol molecules are embedded between phospholipids, maintaining fluidity and structure
• Carbohydrates attach to lipids and proteins, forming glycolipids and glycoproteins

Cell Membrane Functions

• Regulates what enters and leaves the cell through barrier function
• Participates in signal transduction pathways through proteins and lipids
• Facilitates cell-cell interactions through proteins and carbohydrates
• Enables movement of molecules across the membrane through proteins
• Helps identify self and non-self through carbohydrates and proteins

Fluid Mosaic Model

• Phospholipid bilayer is dynamic and flexible, allowing for movement of proteins and lipids
• Proteins and lipids are arranged in a mosaic pattern, with varying degrees of mobility

Cell Transport

• Passive transport: movement of molecules down their concentration gradient through diffusion and osmosis
• Active transport: movement of molecules against their concentration gradient, requiring energy input
• Facilitated diffusion: assisted transport of molecules down their concentration gradient
• Receptor-mediated endocytosis: uptake of molecules into the cell through receptor-mediated vesicle formation

Membrane Properties

• Semipermeable: allows certain molecules to pass through, while restricting others
• Selective permeability: specific molecules are allowed to pass through, while others are restricted
• Permeability coefficients: measure of a molecule's ability to pass through the membrane