MembranesChap. 5

Phosophlipids

Phospholipids will form a bilayer when placed in water.Phospholipid bilayers are fluid.

Membrane StructureCellular membranes have 7 different components:1. Phospholipid bilayer2. Transmembrane protein3. Interior protein network

Membrane StructureCellular membranes have 7 different components:4. Cell surface markers5. Protein pumps6. Cholesterol7. Receptor proteins

Membrane Protein Functions

Diffusion - Passive Transport“Movement of a molecule across a membrane without the use of energy”

Diffusion is a form of passive transport.

Facilitated DiffusionFacilitated diffusion: “Molecules that cannot cross the membrane easily alone can do so with the help of specific proteins”

Active Transport“Movement of a molecule across a membrane with the use of energy”

Sodium-Potassium (Na+ - K+) Pump

Osmosis• The diffusion of water across a semi-

permeable membrane.

Cells in SolutionIsotonic

• “The concentration of water and dissolved solutes is the same on the inside of the cell and in the solution outside”.

Cells in SolutionHypotonic

• “The concentration of dissolved solutes is lower (and the concentration of water is higher) in the solution than in the cell.

Cells in SolutionHypertonic

• “The concentration of dissolved solutes is higher (and the concentration of water is lower) in the solution than in the cell.

Review

Bulk Transport - Endocytosis• The cell

membrane forms a vessicle by surrounding a large molecule or group of molecules.

• The vessicle brings the molecule(s) into the cell.

Bulk Transport - Exocytosis• A vessicle is

created around a molecule inside the cell.

• The vessicle attaches to the cell membrane which opens up and releases the molecule outside the cell.