CP Biology 2013 Cellular Transport The keys to moving materials into and out of cells
Introduction to Cell Transport • What is Transport? • Name of the life process in which materials are exchanged between an organism and its environment
What types of materials need to be transported into/out of living cells? • Water • Glucose • Salt • Ions • Lipids • Amino Acids • Carbon Dioxide • Waste Materials • Ions • Water
Simple and Complex • Can be as simple as moving materials between one celled organism and its environment • OR • As complex as the transport systems in higher organsims • Like Us! (Humans)
In any case below, the FINAL POINT OF TRANSFER IS: The Cell Membrane
All cells live at least PARTLY in touch with WATER • Water-based (aqueous) solutions • In or Out • Substances must cross the cell membrane between the water-based solution on the OUTSIDE of the cell (environment) ORthe water based solution INSIDE of the cell (cytosol/cell solution)
Plants • Think – Which organisms have a cell wall… What polysaccharide makes up cell walls? cellulose Do all cells contain a cell membrain? YES
Boundaries… • Some organisms have cell walls, whereas ALL CELLS contain a cell membrane. • The cell membrane is usually made up of: • Double-layered Sheet LIPID BILAYER • Phospholipid Bilayer • Flexible structure • Forms a strong barrier between the cell and its surroundings.
What does the cell membrane regulate? What enters and leaves the cell and also protects and supports the cell.
Properties of Lipids • 2 main portions…
When these lipids are mixed with water, their hydrophobic fatty acid tails cluster together while their hydrophilic heads are attracted to water. • A lipid bilayer is the result
In the bilayer, which parts of the phospholipids are exposed to the OUTSIDE of the cell (environment) ? “Heads” Hydrophilic Heads!
What happens to the fatty acid tails? They cluster together AWAY from the water and form an OILY layer INSIDE the membrane
Fluid Mosaic Model • Proteinmolecules are embedded in the phospholipid bilayer of most cell membranes. • Because the protein molecules can move around and "float" among the lipids, and because so many different kinds of molecules make up the cell membrane, scientists describe the membrane as a fluid mosaic.
What are these different molecules doing? PROTEINS CARBOHYDRATES Many act like chemical identification cards, allowing individual cells to identify one another. • Form channels/pumps to help move material across the cell membrane. • Attach directly to the cytoskeleton, enabling cells to respond to their environment by using their membranes to help move/change shape
Some materials are allowed to enter and leave the cell… some are NOT! Selectively Permeable… • All cells need to constantly exchange materials with its environment • Many of these materials/substances can cross biological membranes freely. • HOWEVER • Some are too large or too strongly charged to pass across the cell membrane Also known as… Semipermeable
What does it mean if we say that a membrane is IMPERMEABLE to a substance? The substance CANNOT pass across the membrane.
Most biological membranes are selectively permeable, which means… Some substances can pass across the membrane and others cannot! - aka- SEMIPERMEABLE-
How would the following materials move through the cell membrane? Water • moves easily by osmosis • move easily across membrane because very small • charged particles • may or not move easily - depends on molecule and cell. If the cell needs to move it, it will find a mechanism to do so! Small Molecules (O2, CO2) don't move as easily because of charges Any other particles that the cell must have to survive
Diffusion Facilitated Diffusion Osmosis Passive Transport Section 7.3 The movement of materials across the cell membrane without using cellular energy
One of the most important functions of the cell membrane… • Is to keep the cell’s internal conditions relatively constant • MAINTAIN HOMEOSTASIS • The cell must control the transport of materials into/out of the cell Passive Transport Includes: Diffusion, Facilitated Diffusion, and Osmosis
All matter contains a certain amount of heat • This heat causes molecules to spread out into the available space. • Particles are moving constantly • Due to kinetic energy
How does heating a liquid affect the movement of solutes and solvents • It speeds the movement of the particles • It INCREASES the Kinetic Energy
2 examples of solutions (Solutes in a solvent) • Particles in Air (fast) • Perfume • Food Cooking • Foul Odors • Particles in Liquid (slower) • Tea in water • Sugar in sports drink • Chlorine in pool water Every living cell exists in a liquid environment, therefore we can look at the movement of molecules between the solution INSIDE the cell and the solution OUTSIDE the cell.
Click Me! Passive Transport - Diffusion As a result of molecules movingconstantly, collidingwith one another and spreading out randomly, the particles tend to move from an area where they are MORE concentrated to an area where they are LESS concentrated.
Concentration • The amount of particles in a given area (solution) in relation to other particles • Often expressed as a % • Usually the amount of solute PER unit solvent.
Diffusion • The process by which particles move from an area of HIGH concentration to an area of LOWER concentration • Process of diffusion drives the movement of many molecules which move across the cell membrane
Suppose a substance is present in UNEQUAL amounts on either side of a cell membrane • If the substance can cross the membrane the particles will tend to move toward the area where it is ___________ concentrated until it is ___________ distributed. LESS EVENLY
Concentration Gradient • Condition in which the concentrations of particles in 2 given areas are DIFFERENT • Note: each molecule has its own concentration gradient in any given solution
When a solute is first added to a solvent, the concentration gradient is high. • After the solute spreads out, the concentration gradient is low (or nonexistant). • In diffusion, molecules move "down" or "with" the concentration gradient, from higher concentration to lower concentration.
What will happen to the concentration gradient over time as diffusion continues? high gradient low gradient no gradient
Once the concentration of the substance on both sides of the cell membrane is the same… • Equilibrium is reached • Particles of the solution will continue to move across the membrane in almost equal numbers • So there is no further net change to the concentration of the solutions inside or outside the cell.
Dynamic Equilibrium • condition in which the concentrations of solute particles in a given area is equal throughout the entire area. • NO CONCENTRATION GRADIENT REMAINS. ("no net movement")
When dynamic equilibrium is reached, diffusion is equal in all directions.Do the molecules in the solution stop moving? No – they are moving equally in all directions
Passive Transport the movement of materials across the cell membrane without using cellular energy
Facilitated Diffusion Molecules which pass most easily through the cell membrane tend to be small and uncharged, allowing them to dissolve easily in the membrane's lipid environment. However, some substances seem to pass more quickly through the membrane than they should - as though they have a shortcut through the membrane Examples: Ions like Cl- and the sugar Glucose
How does this happen • Proteinsin the cell membrane act as carriersor channelsmaking it easy for certain molecules to cross.
Facilitated Diffusion • Process in which molecules that cannot directly diffuse across the cell membrane pass through special protein channels • Examples: • Red Blood Cells – have protein carriers to allow glucose to pass in/out of the cell.
CLICK ME! There are hundreds of examples of these special proteins which are very specific (like enzymes) and change shape in order to allow the passage of certain substances into or out of the cell. Although facilitated diffusion is FAST & SPECIFIC it is still diffusion so it does NOT require any energy from the cell. Also the net movement will still tend to be with or along the concentration gradient (high low). ATP is not needed and it will continue until equilibrium is reached.
Osmosis An example of Facilitated Diffusion
Why would water molecules normally have a hard time getting across the cell membrane? • The inside of a cell’s lipid bilayer is hydrophobic (water hating) Click me!
Aquaporins • Most cells have special water channel proteins • Known as – Aquaporins • Allow H2O to pass right through them by facilitated diffusion. • This EXTREMELY important process is = OSMOSIS
Osmosis • The diffusion of water through a selectively permeable membrane. • Deals ONLY with the diffusion of WATER • The molecules (in this case, water - not solute molecules) will tend to move from an area of high (water)concentration to an area of low(water)concentration until equilibrium is reached.
Describing the solution concentration OUTSIDE the cell relative to the solute concentration INSIDE the cell Predicting the Direction of Osmosis in cells The direction of water movement into or out of a cell can have dire consequences on the survival of a cell. By knowing the concentrations of solute and solvent on the inside and outside of a cell, we can predict the direction of osmosis and the result on the cell.
Solutions on the outside of a cell (in its environment) can be described based on how they affect the cell: NOTE: (*tonic = solute. [High] solute means [low] water) "HYPER" = HIGH; "HYPO" = LOW; "ISO" = equal or same.
Solute and solvent concentrations can be expressed as percentages of the entire solution. • When added together, the solute and solvent concentrations must equal 100%. A solution with a 10 % solute concentration has a 90% solvent concentration. **Note: in cells, the "solvent" is generally assumed to be water since cell solutions are aqueous.**