Plasma Membrane Structure and Function

Plasma Membrane Made of a Lipid Bi-layer (two parts) Phospholipid heads are hydrophilic (water loving) Phospholipid tails are hydrophobic (water fearing) Described as a Fluid-mosaic. Proteins, glycolipids, carbohydrates, and cholesterol are embedded in the bi- layer.

Fluid Mosiac Model? This refers to the property of the bi-layer which can move sideways in relation to each other. Cells are flexible/pliable due to this property. Also, the bi-layer is studded with several different types of proteins. Each protein has a different function.

Proteins found in bi-layer Channel Proteins: substance can move freely through. Carrier Proteins: using a substrate to help move substances across the membrane. Receptor protein: has a shape that allows a specific molecule to bind to it, causing protein to react. Enzymatic protein: carry out metabolic reactions.

Passive Transport Diffusion: movement of molecules from an area of high concentration to an area of low concentration. Osmosis: the movement of WATER molecules from an area of high concentration to an area of low concentration. Facilitated transport: movement of molecules (like diffusion) using a transport proteins. NONE OF THESE MECHANISMS USE ENERGY.

Facilitated Diffusion of glucose from liver cells.

Active Transport Ion pumps –Molecules can be positively or negatively charged. –Must use ATP to move ions against a concentration & electrical gradient. Cotransport –Uses the element Hydrogen to assist in the uptake of molecules. Endocytosis/Exocytosis –The cell literally taking something inside/outside by engulfing or receptor mediation/expulsion. These mechanisms require energy to move molecules.

Ion Pump

Active Transport (cont.) Exocytosis: the expulsion of materials from a cell by the fusion of a vesicle with the plasma membrane. rt/para_exo.wmvhttp:// rt/para_exo.wmv

Tonicity? Cells are continually adjusting the composition of liquids inside and outside of the cells. The different mixtures are categorized due to their effects on a cell. –Hypertonic solutions –Hypotonic solutions –Isotonic solutions ea_hyper.wmv

Hypotonic Solution ansport/elodea_hypo.wmvhttp:// ansport/elodea_hypo.wmv “A” is a cell in a hypertonic solution while “B” is a cell in a hypotonic solution.

Isotonic Solution ansport/blood_isotonic.wmvhttp:// ansport/blood_isotonic.wmv

What does Tonicity do? Cells can regulate the amount of specific dissolved substances within them, thereby regulating the amount of water entering or leaving the cell through osmosis. Plant cells use the principle of tonicity to draw water from the soil to the leaves. The series of cells along the chosen path of water adjust their tonicity to “move” water throughout the entire plant.

Tonicity cont. Medical use in I.V. fluids. I.V. fluids are usually hypotonic. Why? What advantage would there be for an isotonic I.V. solution? What is the make up of a sport’s drink?