Biology Chapter: Membrane Structure and Fluidity

Study Notes

Membrane fluidity depends on the type of fatty acids and cholesterol between the phospholipids.
Unsaturated fatty acids have bends in their chains, making them harder to pack together and increasing fluidity.
Saturated fatty acids are straight and pack together more tightly, leading to less fluidity.
Cholesterol regulates membrane fluidity by acting as a modulator.
At high temperatures, cholesterol binds to phospholipids to prevent them from becoming too fluid.
At low temperatures, cholesterol prevents phospholipids from packing too densely to increase fluidity.

The plasma membrane is composed of a phospholipid bilayer with embedded proteins.
Integral membrane proteins pass through the membrane and have both hydrophilic and hydrophobic regions.
Peripheral proteins are located on the surface of the membrane and can have various functions.
Glycoproteins have chains of sugars (oligosaccharides) attached, serving as cell recognition signals.

The cell membrane controls what enters and leaves the cell.
There are two main types of membrane transport: passive transport and active transport.

Simple diffusion: movement of particles from a region of high concentration to low concentration, requiring no energy.
Small, non-polar, and non-charged particles can diffuse directly through the phospholipid bilayer.
Facilitated diffusion: movement of particles across a membrane with the help of transport proteins, still along the concentration gradient.
Osmosis: movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration.

Hypotonic solutions have a lower solute concentration than hypertonic solutions.
Water moves from a hypotonic solution to a hypertonic solution to equalize the concentration of free-moving water molecules.
Animal cells lack a cell wall and use contractile vacuoles to regulate osmotic conditions in unicellular organisms.
Plant cells have a cell wall and a large vacuole.

Osmolarity is a measure of solute concentration in a liter of water.
Hypertonic solutions have a high solute concentration.
Hypotonic solutions have a low or no solute concentration.
Isotonic solutions have the same solute concentration on both sides of a membrane.