Cell Membrane & CELLULAR TRANSPORT

THE CELL MEMBRANE REMEMBER…The cell membrane controls the movement of substances into and out of the cell.

Types of Transport Mechanisms Active Processes Primary Active Transport Na+/K+ pump Secondary Active Transport Coupled transport Endocytosis Phagocytosis Pinocytosis Receptor-mediated endocytosis Exocytosis Membrane vesicle Passive Processes Diffusion Direct Facilitated Diffusion Protein carrier Protein channel* Osmosis Aquaporins

“COME ON AND TAKE A FREE RIDE” – PASSIVE TRANSPORT No ATP (energy) needed There are three types: DIFFUSION -Small molecules (CO2, H2O, O2, salts) can move between the phospholipid molecules of the bilayer. -Molecules move from a HIGH concentration ([]) to a LOW [] along a CONCENTRATION GRADIENT until a balance is achieved.

Diffusion

Diffusion

Direct Diffusion Non-polar molecules easily cross non-polar interior of cell membrane movement from [high] to [low] Example: Movement of O2 into cells from blood

Diffusion

Passive Transport 2. OSMOSIS -The movement of water (from High to Low [ ]) through a selectively permeable membrane.

Comparing Osmosis and Diffusion Osmosis is the movement of water across a cell membrane from an area of higher concentration to an area of lower concentration. Diffusion is the movement of molecules other than water across a membrane from an area of higher concentration to and area of lower concentration.

How Osmosis Works

Osmosis and Random Motion

Osmotic Conditions Surrounding Cells Isotonic solution – Solute [ ] outside of cell is equal to [ ] inside the cell. Cell remains normal. Hypertonic solution – Fluid surrounding the cell has a higher solute [ ] than inside. Water diffuses out and the cell shrinks! Hypotonic solution – [ ] of solute is higher inside the cell than outside. Water will diffuse into the cell. The cell expands!

Passive Transport Osmosis is a VITAL fluid control process (blood and urine balance)

Learning Check: Wake up! Pg 74 # 25 – 30 25) What is a concentration gradient? 26) Describe diffusion. Why does it occur? 27) What are three factors that affect diffusion. How do they work?

28) What are the similarities and Differences between diffusion and osmosis? 29) If membranes were not semi-permeable, could diffusion/osmosis occur? 30)Why are diffusion/osmosis examples of passive transport?

Passive Transport 3. FACILITATED DIFFUSION -Some proteins in the cell membrane provide a “tunnel” for larger molecules (glucose) to diffuse through. -They go with the concentration gradient!

Protein Channel Diffusion Polar molecules cannot easily cross non-polar interior of cell membrane Pass through a hydrophilic protein channel movement from [high] to [low] Example: Movement of ions in or out of the cell

Protein Channel Diffusion

Facilitated Diffusion – Protein Carrier Entry of certain polar molecules into the cell must be tightly regulated Molecules bind to specific carrier proteins to be transported across movement from [high] to [low] 3 key characteristics Specific Passive Saturation Example: Movement of glucose into the cells

Facilitated Diffusion

Extension…Sports Drinks! Can you drink yourself to death?? Should the tonicity of a fluid replacement drink be isotonic, hypertonic or hypotonic???

Hypernatremia Certain conditions may result in a decrease in the sodium concentration in interstitial fluid. For instance, during sweating the skin excretes sodium as well as water. If we replace the lost fluid with plain water then we may produce a sodium deficit. The decrease in sodium concentration in the interstitial fluid lowers the osmotic pressure. Water moves from the interstitial fluid into the cells, producing two results that can be quite serious:

Hypernatremia The first result, an increase in intracellular water concentration (water in the cell), called over hydration which disrupts nerve cell function. In severe over-hydration we may see disoriented behaviour, convulsions, coma, and even death The second result is a loss of interstitial fluid volume that leads to a decrease in the interstitial fluid pressure. As the pressure drops, water moves out of the plasma, resulting in a loss of blood volume that may lead to circulatory shock.

Sports Drinks!

Isotonic - quickly replaces fluids lost by sweating and supplies a boost of carbohydrate. This drink is the choice for most athletes - middle and long distance running or team sports. Glucose is the body's preferred source of energy therefore it may be appropriate to consume Isotonic drinks where the carbohydrate source is glucose in a concentration of 6% to 8% Hypotonic - quickly replaces fluids lost by sweating. Suitable for athletes who need fluid without the boost of carbohydrate e.g. jockeys and gymnasts. Hypertonic - used to supplement daily carbohydrate intake normally after exercise to top up muscle glycogen stores. In ultra distance events, high levels of energy are required and Hypertonic drinks can be taken during exercise to meet the energy demands. need to be used in conjunction with Isotonic drinks to replace fluids.

ACTIVE TRANSPORT ATP is the energy used to “pump” nutrients across cell membranes. Using ATP, carrier proteins “pump” substances through a membrane from an area of LOW [ ] to an area of HIGH [ ] against the concentration gradient. Eg. Page 76…the Na+/K+ pump in nerve cells

ACTIVE TRANSPORT

Active Transport Primary Active Transport Uses ATP to move molecules from one side of the membrane to another, UP the concentration gradient Example: Na + /K + pump or H+ pump

Na/K Pump

Active Transport Secondary Active Transport With 3 Na+ moving OUTside the cell for every 2 K+ moving in, what would happen to the difference in charge across the cell? This combination of a charge buildup with a concentration gradient is called an electrochemical gradient This electrochemical gradient can serve as the energy source (not ATP), and can be ‘coupled’ with transport of other molecules  “coupled transport”

Coupled Transport

Learning Check Page 77 # 31 - 36

A QUESTION! HOW DO THE REALLY LARGE MOLECULES (Hormones, polysaccharides etc.) move in and out of cells??

An Answer!! By two processes called ENDOCYTOSIS AND EXOCYTOSIS. Both methods require the use of vesicles and ATP!

ENDOCYTOSIS –Moving materials into the cell Three Types… Phagocytosis (Cell Eating): -Used by white blood cells and amoeba. -The cell moves out and surrounds the solid particle.

ENDOCYTOSIS –Moving materials into the cell 2. Pinocytosis (Cell drinking) -Same process as phagocytosis except the cell is moving liquids.

Phagocytosis

ENDOCYTOSIS –Moving materials into the cell 3. RME – Receptor Mediated Endocytosis -Special receptor molecules on the membrane bind with the large molecule to be moved. -When enough receptor molecules have gathered in one place, pinocytosis occurs. -E.g. Moving cholesterol into the cell.

EXOCYTOSIS – Moving materials out of the cell The reverse of endocytosis The vesicle (from the Golgi) fuses with the membrane and releases it’s contents out of the cell. E.g. Hormones