Cell Membrane

Cell membrane A gateway and a barrier for the cell. Controls what enters & exits composed of phospholipids and proteins.

Phospholipids Made up of a polar head and a nonpolar tail. Head – water loving Tails – water hating Tails stay to inside of bi-layer to avoid contact with water. Nonpolar Polar Lipid Bilayer:

Proteins Marker Proteins – attach to carbohydrates on cell surface that identifies cell type. Receptor Proteins – recognize and bind to specific substances outside the cell

Transport Proteins –helps substances move across the membrane.

Passive Transport Requires NO energy Goes down its “concentration gradient” 3 types – 1) diffusion, 2) osmosis, 3) facilitated diffusion

Diffusion net movement of molecules from a region of high concentration to a region of lower concentration With the “concentration gradient” NO ENERGY REQUIRED Ex: perfumes from a bouquet spreads across room

Osmosis diffusion of water across cell membranes NO ENERGY REQUIRED Ex: lysing of a blood cell.

Facilitated Diffusion the diffusion of a substance moving with the concentration gradient, but which require the assistance of other molecules. NO ENERGY REQUIRED The “facilitation” is physically turning a molecule so that it may more easily pass through a membrane

Active Transport movement of molecules from a region of low concentration to a region of high concentration. This is against the “concentration gradient” Requires ENERGY!!!

Three main types of active transport movement directly across the cell membrane with assistance from transport proteins EX: sodium-potassium pump helps nerve cells to pass their signals in the form of electrical impulses maintain a higher concentration of potassium ions inside the cells compared to outside, and a higher concentration of sodium ions outside of cells compared to inside

Sodium potassium pump

Two main types of active transport endocytosis - is an infolding and then pinching in of the cell membrane so that materials are engulfed into a vacuole or vesicle within the cell Phagocytosis solid particles taken into the cell

Two main types of active transport Exocytosis – substances are released from the cell through a vesicle that transports the substance to the cell surface and then fuses with the membrane to let the substance out of the cell.