Cell Transport Membranes Structure and Function

Membrane Structure Phospholipid Bi-layer Phospholipid Bi-layer Contains Different Types of Proteins Contains Different Types of Proteins –Channel proteins –Protein Pumps proteins –Adhesion proteins –Cell-to-Cell Communication proteins –Hormone Receptor proteins –Immobilized Enzymes Fluid Mosaic Model Fluid Mosaic Model

Phospholipid Bi-layer Contains Glycoproteins Glycoproteins Integral Proteins Integral Proteins Peripheral Proteins Peripheral Proteins Cholesterol Cholesterol

Channel proteins Integral protein: embedded across bi-layer Integral protein: embedded across bi-layer Allows for movement of molecules across cell membrane Allows for movement of molecules across cell membrane

Membrane Function Boundary Separates Two Environments Boundary Separates Two Environments Selectively Permeable Selectively Permeable Passive Transport Passive Transport –Simple Diffusion –Facilitated Diffusion Active Transport Active Transport –Protein Pumps Endocytosis / Exocytosis Endocytosis / Exocytosis

Selectively Permeable Membranes and their proteins allow only certain molecules to cross Membranes and their proteins allow only certain molecules to cross Diffusion: movement of a substance from an area of high concentration to low concentration Diffusion: movement of a substance from an area of high concentration to low concentration Osmosis: movement of water from an area of low solute concentration to high Osmosis: movement of water from an area of low solute concentration to high

Diffusion

Osmosis

Passive Transport The movement of a molecule across a membrane from high to low concentration Molecules move with the concentration gradient Simple Diffusion Simple Diffusion –No proteins needed Facilitated Diffusion Facilitated Diffusion –Membrane proteins required

Simple Diffusion Small, uncharged molecules can move directly across membrane Small, uncharged molecules can move directly across membrane Includes gases (CO 2 and 0 2 ) and water Includes gases (CO 2 and 0 2 ) and water

Facilitated Diffusion Uses either protein channels or transporters (change shape) Uses either protein channels or transporters (change shape) ChannelTransporter

Passive Transport

Active Transport Movement of molecules across a membrane from low concentrations to high Movement of molecules across a membrane from low concentrations to high Molecules move against the concentration gradient Molecules move against the concentration gradient Requires a protein transporter (pump) and energy supplied by ATP Requires a protein transporter (pump) and energy supplied by ATP Ex. sodium/potassium pump Ex. sodium/potassium pump

Active Transport

Passive Vs. Active Transport

Endocytosis Cell membrane surrounds and engulfs food particle or extra-cellular fluid Cell membrane surrounds and engulfs food particle or extra-cellular fluid Results in vesicle inside cell Results in vesicle inside cell Phagocytosis: engulfing large particles like bacteria Phagocytosis: engulfing large particles like bacteria Pinocytosis: engulfing extra-cellular fluid and whatever it might contain Pinocytosis: engulfing extra-cellular fluid and whatever it might contain

Exocytosis Opposite of endocytosis Opposite of endocytosis Vesicle containing secretory proteins or wastes joins with plasma membrane Vesicle containing secretory proteins or wastes joins with plasma membrane Molecules inside vesicle are then released outside of the cell Molecules inside vesicle are then released outside of the cell

Summary