Membrane Structure and Function The plasma membrane controls what enters and leaves the cell.

Plasma Membrane Structure

Lipid bilayer Lipid bilayer Hydrophilic heads Hydrophilic heads Hydrophobic tails Hydrophobic tails Proteins: Allow the passage of some molecules Proteins: Allow the passage of some molecules Carbohydrates: Cell recognition, Carbohydrates: Cell recognition, Occur on the outside cell surface only Occur on the outside cell surface only Cholesterol: makes membranes Cholesterol: makes membranes less fluid at warm temperatures (37 degrees) less fluid at warm temperatures (37 degrees) more fluid at cold temperatures more fluid at cold temperatures

Fluid Mosaic Model Membranes must be fluid to work properly. Membranes must be fluid to work properly. The membrane is composed of many types of proteins embedded in two layers of phospholipids. Therefore a mosaic. The membrane is composed of many types of proteins embedded in two layers of phospholipids. Therefore a mosaic.

Traffic Across the Membrane Passive Transport vs. Active Transport Passive Transport vs. Active Transport Passive Transport does not require energy (ATP) from the cell. Passive Transport does not require energy (ATP) from the cell. Active Transport does require the input of cell energy (ATP). Active Transport does require the input of cell energy (ATP).

Passive Transport Diffusion- the net movement of molecules from an area of high concentration to an area of lower concentration. Diffusion- the net movement of molecules from an area of high concentration to an area of lower concentration.

Passive Transport Solutions Solutions Hypertonic: greater concentration of solutes Hypertonic: greater concentration of solutes Hypotonic: lower concentration of solutes Hypotonic: lower concentration of solutes Isotonic: concentration of solutes is equal Isotonic: concentration of solutes is equal

Passive Transport: Osmosis Osmosis- The diffusion of water across a membrane.

Behavior of Cells in Different Solutions

Passive Transport: Facilitated Diffusion Facilitated Diffusion: The diffusion of molecules with the help of a transport protein. Facilitated Diffusion: The diffusion of molecules with the help of a transport protein.

Active Transport Many cells must move molecules against their concentration gradient (from areas of low concentration to higher concentration). Many cells must move molecules against their concentration gradient (from areas of low concentration to higher concentration). This requires the input of cell energy (ATP). This requires the input of cell energy (ATP).

The Sodium Potassium Pump

Bulk Transport Endocytosis- Bulk movement of materials into the cell by means of a vesicle. Endocytosis- Bulk movement of materials into the cell by means of a vesicle. Exocytosis- Bulk movement of materials out of the cell by means of a vesicle. Exocytosis- Bulk movement of materials out of the cell by means of a vesicle.