PLAMA MEMBRANE FUNCTION OF THE PLASMA MEMBRANE Provides

PLAMA MEMBRANE

FUNCTION OF THE PLASMA MEMBRANE Provides a boundary between a cell and its environment Controls the flow of material in and out of the cell The membrane is selectively permeable, which means that it lets some substances pass through, but not everything. Maintains homeostasis: balance within the cells � Allows more water and food to come in when needed, gets rid of what is not needed

RELATING THE STRUCTURE TO ITS FUNCTION 1. The membrane is a bilayer (2 layers). 2. Made up molecules which are a glycerol backbone, 2 fatty acids, and a phosphate group; called the phospholipid bilayer. 3. The polar head and nonpolar tail – fatty areas that attract and repel water. � A. make the membrane behave like a fluid 4. Embedded proteins: determine which molecules can go in and out of the cell. � A. Serves as recognition markers

THE FLUID MOSAIC MODEL The phospholipid bilayer allows other molecules to “float” in the membrane. � Think of the phospholipids in the bilayer as creating a “sea” where other molecules can float on top, like a barrel of apples floating on top of the water.

PROTEINS IN THE PLASMA MEMBRANE Transmit signals inside the cell Act as a support structure Provide pathways for substances to enter and leave.

CHOLESTEROL IN THE PLASMA MEMBRANE Prevents fatty acid tails from sticking together

CARBOHYDRATES IN THE PLASMA MEMBRANE Identify chemical signals

PASSIVE TRANSPORT 1. Passive Transport - Particles move from an area of high concentration to an area of low concentration. A. Cell does not require energy input. B. “Facilitated diffusion” C. Ex. When you leave the classroom you will all go the same direction down the hallway (ex. Diffusion) • There • • • are 3 modes of passive transport: 1. Diffusion 2. Facilitated Diffusion 3. Osmosis

DIFFUSION

Diffusion – the net movement of particles from an area where there are many particles of the substance to an area where there are fewer particles of the substance. � A. Difference in the concentration is called a gradient Initial Conditions: Diffusion takes place:

DIFFUSION IN A CELL

FACILITATED DIFFUSION

FACILITATED DIFFUSION -THE MOVEMENT OF MATERIALS ACROSS THE PLASMA MEMBRANE USING PROTEINS. Channel Proteins Carrier Proteins

OSMOSIS

Osmosis – the diffusion of water across a selectively permeable membrane.

3 TYPES OF SOLUTIONS: 1. Isotonic 2. Hypotonic 3. Hypertonic

ISOTONIC SOLUTIONS A. Solutions where the concentration of solutes and water is equal to/the same as the normal cells of the body and the blood B. Movement into the cell = water goes in both directions (in and out)

HYPOTONIC SOLUTION A. Concentration of salt is lower than in normal cells of the body and blood. B. Water will move into the cell to equalize C. Increases osmotic pressure: pressure the generated as the water flows through the plasma membrane D. Cell could burst if it takes in too much water.

HYPERTONIC SOLUTIONS A. Concentration of the solute outside of the cell is higher than inside the cell. B. Water rushes out of the cell C. Can result in the cell shrinking – water goes out of plant cell causing it to wilt

1. Passive Transport - Particles move from an area of high concentration to an area of low concentration. A. Cell does not require energy input. B. “Facilitated diffusion” C. Ex. When you leave the classroom you will all go the same direction down the hallway (ex. Diffusion)

ACTIVE TRANSPORT Move from an area of low concentration to an area of high concentration – transport against the gradient A. Requires energy to move items into the cell B. Ex. Everyone going down the hallway in the same direction except for you, must exert energy to get past everyone.

ACTIVE TRANSPORT USING CARRIER PROTEINS

TYPES OF ACTIVE TRANSPORT PUMPS Na+/K+ ATPase pump �Moves three Na+ ions out of the cell and two K + ions into the cell to maintain the level of these ions inside and outside of the cell. ADD DEMONSTRATION OF NA/K PUMP HERE

ENDOCYTOSIS The process by which the cell surrounds and takes particles into the cell.

EXOCYTOSIS Secretion of material out of the plasma membrane

COMPARING ENDOCYTOSIS AND EXOCYTOSIS Endocytosis: Surrounds and takes substances into the cell Transports substances too large to move across the plasma membrane Exocytosis: Surrounds and expels or secretes substances